Positive Work Contribution Shifts from Distal to Proximal Joints during a Prolonged Run

Effect of Footwear Longitudinal Bending Stiffness on Energy Cost, Biomechanics, and Fatigue during a Treadmill Half-Marathon

INTRODUCTION

Carbon plates have been used to increase running shoes' longitudinal bending stiffness (LBS), but their effect during a long duration run remains unknown. Our study aimed to identify the effect of LBS on energy cost of running (Cr), biomechanics, and fatigue during a half-marathon.

METHODS

Thirteen well-trained male runners (half-marathon time <1 h 40) performed two half-marathons at 95% of the running speed associated with their second ventilatory threshold on two separate visits, with either high-LBS (HLBS) shoes, with carbon plates) or standard-LBS (SLBS) shoes. Before and after the half-marathon, Cr at 12 km·h -1 with both shoes (two 6-min bouts: Cr12) and ankle plantar flexor (PF) force were measured. During the half-marathon, running kinematics, shoe perceived comfort, and Cr were assessed.

RESULTS

During Cr12 measurements before and after the half-marathon, HLBS was 1.0% ± 2.1% more economical than SLBS ( P < 0.001). During the half-marathon, Cr increased with running duration ( P = 0.048), but there was no distance×condition effect. HLBS increased contact time (+3%, P = 0.01), decreased metatarsophalangeal joint dorsiflexion (-9%, P = 0.01), and was perceived less comfortable than SLBS, independently from running duration. At the end of the half-marathon, HLBS shoes led to higher PF force loss (-20.0% ± 9.8% vs -13.3% ± 11.0%, P = 0.048).

CONCLUSIONS

Adding curved carbon plates in the running shoes slightly improved Cr during short running bouts at low intensity but not during a half-marathon. This discrepancy may be explained by day-to-day Cr variability and variation in shoe comfort. PF fatigue was higher with HLBS shoes, but the accentuated fatigue did not further impact the biomechanical perturbations induced by the plates. Our results suggest that carbon plates alone do not provide a significant advantage for half-marathon performance.

Does the Fatigue Induced by a 30-Minute Run Affect the Lower Limb Acceleration Spikes' Asymmetries?

Running-induced fatigue affects several biomechanical parameters, and yet few studies are focused on the acceleration spikes' asymmetries. This study aimed to evaluate the effects of a 30 min run on lower limbs spikes' asymmetries. Eighteen recreational runners (35.6 ± 7.5 years; seven women) performed a treadmill running protocol at a moderate speed and acceleration spikes' asymmetries and kinematic (temporal) parameters were measured via accelerometers-on the tibias and sacrum-and photogrammetry. Acceleration spikes' parameters were continuously measured and averaged per minute to assess the relationship between fatigue and acceleration spike asymmetries via a linear regression model. Right tibial acceleration spikes increased over time (r = 0.9; p < 0.001) and left tibia spikes decreased (r = 0.78; p < 0.001), with a rise in tibial load asymmetry from 9% to 25% at the end (r = 0.98; p < 0.001). This study suggest that fatigue affects the acceleration spikes of the two legs differently, with increasingly greater acceleration spikes in the right (dominant) leg. These findings should be considered, as greater asymmetries are related to overuse injuries and lower efficiency. Also, in studies focusing on running mechanics with fatigue, it is recommended that researchers collect data from both limbs, and not only from the right (dominant) leg.

Mechanical power distribution of the lower limbs changed during intermittent 300 countermovement jumps

PURPOSE

The aim of this study was to investigate the effect of 300 intermittent countermovement jumps (CMJs) on the mechanical power distribution at the joints of the lower limbs and the influence of the upper body to explain vertical jump performance.

METHODS

Fifteen male sport students (age 24.5 ± 2.3 years; body height 1.85 ± 0.06 m; body mass 84.8 ± 8.5 kg) performed a set of intermittent 300 CMJs at maximal effort. An inverse-dynamic approach was used to calculate the mechanical power at the hip, knee, and ankle joint for each jump.

RESULTS

Jump height and mechanical power in the knee and ankle joints decreased significantly (p < .010), while remained the same in the hip joint. In contrast, a significant increased vertical velocity was observed for the upper body segment. In addition, a significant higher angular momentum at the center of mass was detected during the braking and propulsion phase.

CONCLUSION

The findings highlight a fatigue-related decrease in lower limb power, particularly in the knee and ankle joints, which changed the mechanical power distribution at the joints of the lower limbs. The trunk extensor muscles were probably able to counteract the fatigue-related decrease in lower limb power by increased vertical velocity of the upper body segment and higher angular momentum at the center of mass during the braking and propulsion phase. Accordingly, the most effective way to maintain jumping performance in fatigued state would be to improve the fatigue resistance of the knee extensors, ankle plantar flexors, and trunk extensor muscles.

Fatigue assessment in distance runners: A scoping review of inertial sensor-based biomechanical outcomes and their relation to fatigue markers and assessment conditions

BACKGROUND

Fatigue manifests as a decline in performance during high-intensity and prolonged exercise. With technological advancements and the increasing adoption of inertial measurement units (IMUs) in sports biomechanics, there is an opportunity to enhance our understanding of running-related fatigue beyond controlled laboratory environments.

RESEARCH QUESTION

How have IMUs have been used to assess running biomechanics under fatiguing conditions?

METHODS

Following the PRISMA-ScR guidelines, our literature search covered six databases without date restrictions until September 2024. The Population, Concept, and Context criteria were used: Population (distance runners ranging from novice to competitive), Concept (fatigue induced by running a distance over 400 m), Context (assessment of fatigue using accelerometer, gyroscope, and/or magnetometer wearable devices). Biomechanical outcomes were extracted and synthesised, and interpreted in the context of three main study characteristics (cohort ability, testing environment, and the inclusion of physiological outcomes) to explore their potential role in influencing outcomes.

RESULTS

A total of 88 articles were included in the review. There was a high prevalence of treadmill-based studies (n=46, 52%), utilising only 1-2 sensors (n=69, 78%), and cohorts ranged in experience, from sedentary to elite-level runners, and were largely comprised of males (69% of all participants). The majority of biomechanical outcomes assessed showed varying responses to fatigue across studies, likely attributable to individual variability, exercise intensity, and differences in fatigue protocol settings and prescriptions. Spatiotemporal outcomes such as stride time and frequency (n=37, 42 %) and impact accelerations (n=55, 62%) were more widely assessed, with a fatigue response that appeared population and environment specific.

SIGNIFICANCE

There was notable heterogeneity in the IMU-based biomechanical outcomes and methods evaluated in this review. The review findings emphasise the need for standardisation of IMU-based outcomes and fatigue protocols to promote interpretable metrics and facilitate inter-study comparisons.

Does high-intensity running to fatigue influence lower limb injury risk?

OBJECTIVES

The aim of this study was to quantify changes in peak bending moments at the distal tibia, peak patellofemoral joint contact forces and peak Achilles tendon forces during a high-intensity run to fatigue at middle-distance speed.

DESIGN

Observational study.

METHODS

16 high-level runners (7 female) ran on a treadmill at the final speed achieved during a preceding maximum oxygen uptake test until failure (~3 min). Three-dimensional kinetics and kinematics were used to derive and compare tibial bending moments, patellofemoral joint contact forces and Achilles tendon forces at the start, 33 %, 67 % and the end of the run.

RESULTS

Average running speed was 5.7 (0.4) m·s-1. There was a decrease in peak tibial bending moments (-6.8 %, p = 0.004) from the start to the end of the run, driven by a decrease in peak bending moments due to muscular forces (-6.5 %, p = 0.001), whilst there was no difference in peak bending moments due to joint reaction forces. There was an increase in peak patellofemoral joint forces (+8.9 %, p = 0.026) from the start to the end of the run, but a decrease in peak Achilles tendon forces (-9.1 %, p < 0.001).

CONCLUSIONS

Running at a fixed, high-intensity speed to failure led to reduced tibial bending moments and Achilles tendon forces, and increased patellofemoral joint forces. Thus, the altered neuromechanics of high-intensity running to fatigue may increase patellofemoral joint injury risk, but may not be a mechanism for tibial or Achilles tendon overuse injury development.

Durability of Running Economy: Differences between Quantification Methods and Performance Status in Male Runners

INTRODUCTION

Running economy (RE) deteriorates during prolonged running, although the effect of measuring energy cost (EC) or oxygen cost (OC) on the magnitude of these changes has not been investigated. Similarly, it is unknown if runners' performance level may influence the deterioration of RE during prolonged running. The aims of this study were to compare changes in EC and OC measurements of RE during a prolonged run in a large cohort of well-trained male runners, and to compare changes between runners of high- and low-performance standard.

METHODS

Forty-four male runners (maximal oxygen uptake (V̇O 2max ) 62.4 mL·kg -1 ·min -1 ; 10-km time: 35:50 ± 4:40 mm:ss) completed an incremental test determining lactate threshold 1 (LT1) and V̇O 2max , and on a separate occasion, a 90-min run at LT1. Respiratory gases were collected at 15-min intervals. Subsequently, subgroups of high- (HP; 10-km time: 31:20 ± 01:00 mm:ss) and low-performing (LP; 10-km time: 41:50 ± 01:20 mm:ss) runners were compared.

RESULTS

RE deterioration was only fractionally larger when expressed as OC than EC (0.1% greater from 30-90 min; P < 0.001), perhaps due to the small change in respiratory exchange ratio (-0.01) in this study. For the HP group, increases were lower than LP after 90 min in both EC (+2.3% vs +4.3%; P < 0.01) and OC (+2.4% vs +4.5%; P < 0.01). Similarly, at standardized distances, changes were lower for HP versus LP, for example, at 16.7 km + 1.0 versus +3.2% for EC ( P < 0.01), and +1.2 vs +3.4% for OC ( P < 0.001).

CONCLUSIONS

The deterioration of RE was dependent on athlete's performance level, with HP runners displaying superior RE durability. The use of EC or OC had only a fractional influence on RE durability, although this may gain importance with larger shifts in substrate metabolism.

Fatigue-Related Changes in Running Technique and Mechanical Variables After a Maximal Incremental Test in Recreational Runners

Understanding the changes in running mechanics caused by fatigue is essential to assess its impact on athletic performance. Changes in running biomechanics after constant speed conditions are well documented, but the adaptive responses after a maximal incremental test are unknown. We compared the spatiotemporal, joint kinematics, elastic mechanism, and external work parameters before and after a maximal incremental treadmill test. Eighteen recreational runners performed 2-minute runs at 8 km·h-1 before and after a maximal incremental test on a treadmill. Kinematics, elastic parameters, and external work were determined using the OpenCap and OpenSim software. We did not find differences in spatiotemporal parameters and elastic parameters (mechanical work, ankle, and knee motion range) between premaximal and postmaximal test conditions. After the maximal test, the runners flexed their hips more at contact time (19.4°-20.6°, P = .013) and presented a larger range of pelvis rotation at the frontal plane (10.3°-11.4°, P = .002). The fatigue applied in the test directly affects pelvic movements; however, it does not change the lower limb motion or the spatiotemporal and mechanical work parameters in recreational runners. A larger frontal plane motion of the pelvis deserves attention due to biomechanical risk factors associated with injuries.

Managing lower extremity loading in distance running by altering sagittal plane trunk leaning

BACKGROUND

Trunk lean angle is an underrepresented biomechanical variable for modulating and redistributing lower extremity joint loading and potentially reducing the risk of running-related overuse injuries. The purpose of this study was to systematically alter the trunk lean angle in distance running using an auditory real-time feedback approach and to derive dose-response relationships between sagittal plane trunk lean angle and lower extremity (cumulative) joint loading to guide overuse load management in clinical practice.

METHODS

Thirty recreational runners (15 males and 15 females) ran at a constant speed of 2.5 m/s at 5 systematically varied trunk lean conditions on a force-instrumented treadmill while kinematic and kinetic data were captured.

RESULTS

A change in trunk lean angle from -2° (extension) to 28° (flexion) resulted in a systematic increase in stance phase angular impulse, cumulative impulse, and peak moment at the hip joint in the sagittal and transversal plane. In contrast, a systematic decrease in these parameters at the knee joint in the sagittal plane and the hip joint in the frontal plane was found (p < 0.001). Linear fitting revealed that with every degree of anterior trunk leaning, the cumulative hip joint extension loading increases by 3.26 Nm·s/kg/1000 m, while simultaneously decreasing knee joint extension loading by 1.08 Nm·s/kg/1000 m.

CONCLUSION

Trunk leaning can reduce knee joint loading and hip joint abduction loading, at the cost of hip joint loading in the sagittal and transversal planes during distance running. Modulating lower extremity joint loading by altering trunk lean angle is an effective strategy to redistribute joint load between/within the knee and hip joints. When implementing anterior trunk leaning in clinical practice, the increased demands on the hip musculature, dynamic stability, and the potential trade-off with running economy should be considered.

How Humans Run Faster: The Neuromechanical Contributions of Functional Muscle Groups to Running at Different Speeds

How the neuromechanics of the lower limb functional muscle groups change with running speed remains to be fully elucidated, with implications for our understanding of human locomotion, conditioning, and injury prevention. This study compared the neuromechanics (ground reaction and joint kinetics, kinematics and muscle activity) of middle-distance athletes running on an instrumented treadmill at six wide-ranging speeds (2.78-8.33 m·s-1). Ground reaction forces and kinematics were analyzed using inverse dynamics to calculate flexor and extensor joint torques, and positive and negative work done by these torques. Contributions of each functional muscle group to the total positive and negative work done by the limb during stance, swing, and the whole stride were quantified. During stance, the ankle plantar flexors were the major energy generator and absorber (>60%) at all speeds, but their contribution to whole stride energy generation and absorption declined with speed. Positive work by the hip extensors rose superlinearly with speed during stance (3-fold) and especially during swing (12-fold), becoming the biggest energy generator across the whole stride at >5 m·s-1. Knee flexor and extensor negative work also rose superlinearly with speed during swing, with the knee flexors becoming the greatest energy absorber over the whole stride at >7.22 m·s-1. Across speeds, plantar flexor peak moment and positive work accounted for 97% and 96% of the variance in step length, and swing hip extension peak moment and positive work accounted for 98% and 99% of the variance in step frequency. There were pronounced speed, phase (stance/swing), and work (positive/negative) dependent contributions of the different functional muscle groups during running, with extensive implications for conditioning and injury prevention.

Curved carbon plates inside running shoes modified foot and shank angular velocity improving mechanical efficiency at the ankle joint

Recent technologically advanced running shoes have been designed with higher stack height and curved carbon plate-reinforced toe springs to enhance running performance. The purpose of this study was to examine how curved carbon-plate reinforcement modulated mechanical efficiency at the ankle joint during the running stance phase. We prepared two footwear conditions: Non and Carbon, both had a 3D-printed midsole (40-mm heel thickness). A full-length curved carbon plate was inserted along the toe spring in Carbon. The participants included 14 non-rearfoot long-distance athletes. They were required to run at a speed of 12 km/h on a 20-m runway with both shoes. Mechanical-energy expenditure (MEE, indicating mechanical work) and compensation (MEC, indicating mechanical efficiency) were calculated in the following mechanical-energy transfer phases: concentric, eccentric, and no-transfer. Running with Carbon exhibited improved MEC and reduced MEE at the ankle joint during the concentric transfer phase than with Non. The improvement in the concentric MEC at the ankle joint indicates that a larger amount of mechanical energy is transferred from the shank into the foot segment that compensates for the force exerted by the plantar flexor muscles, which implies more mechanically efficient plantarflexion movement. As the ankle joint is the largest energetic contributor in the running stance phase, greater MEC and lower MEE and torque at the ankle joint could improve running performance. Hence, the curved carbon plate may be a key feature of advanced footwear technology.

Footstrike patterns and race performance in the 2017 IAAF World Championship men's 10,000 m final

Midfoot- (MFS) and forefoot-striking (FFS) runners usually switch to rearfoot-striking (RFS) during marathons. However, world-class runners might resist modifications during shorter races. The purpose of this study was to analyse footstrike patterns, ground contact times and running speeds in a World Championship men's 10,000 m final. Footstrike patterns and contact times of the top 12 finishing men (24 ± 5 years) were recorded (150 Hz) during laps 1, 5, 11, 15, 20 and 25. Split times for each 100-m segment were obtained. No RFS patterns were observed; there was no difference between the number of FFS and MFS athletes at any distance (p ≥ 0.581) and no change in the proportions of FFS and MFS occurred (p = 0.383). No link between race performance and footstrike pattern appeared given the similar number who used FFS or MFS and their similar finishing times. Despite slower running speeds and longer contact times in the middle of the race (p ≤ 0.024), no effect on footstrike patterns occurred. The prevalence of anterior footstrike patterns in this world-class race reflects the capability of maintaining fast paces (>22 km/h). Changes in footstrike pattern might accompany the physiological and neuromuscular effects of fatigue over longer distances.

Human‐in‐the‐loop optimized rocker profile of running shoes to enhance ankle work and running economy

Increasing the efficiency at which muscles generate mechanical power could improve running economy. A potential way to reduce muscle fiber shortening velocities and enhance energy storing of the Triceps Surae is changing their gear ratio at the ankle via optimization of shoe rollover profile. The aim of the current study was to individually optimize rollover profile of rocker shoes via human‐in‐the‐loop optimization to maximize positive ankle work to redistribute joint work from the hip and knee to the ankle and improve running economy. A total of 10 runners ran on a treadmill with experimental rocker shoes in which apex position and angle were optimized using an evolution algorithm to maximize positive ankle work. We compared experimental shoes with optimal settings, standard settings, and control shoes in terms of biomechanics and running economy. Optimal apex parameters differed considerably between participants. The optimal condition resulted in higher positive ankle work and a higher proportional share of the ankle in the total positive lower limb work compared to the standard condition. A difference in running economy between these conditions was not found. Human‐in‐the‐loop optimization can redistribute joint work from the hip and knee to the ankle by individually optimizing apex parameters. Although this did not improve running economy, the study showed that human‐in‐the‐loop optimization could improve the effectiveness of footwear with respect to the selected optimization parameter on an individual level.

Human‐in‐the‐loop optimization is able to individually optimize apex position and apex angle of running shoes to enhance ankle work The increase in positive ankle work results in a redistribution of positive work generated around the lower limb joints from the hip and knee to the ankle The increase ankle work did not result in an increased running economy and therefore it should be further investigated which factors confound the theoretical benefit

Gender differences on the age-related distal-to-proximal shift in joint kinetics during running

The increased running participation in women and men over 40 years has contributed to scientific interest on the age-related and gender differences in running performance and biomechanics over the last decade. Gender differences in running biomechanics have been studied extensively in young runners, with inconsistent results. Understanding how gender influences the age-related differences in running mechanics could help develop population-specific training interventions or footwear to address any potential different mechanical demands. The purpose of this study was to assess gender and age effects on lower limb joint mechanics while running. Middle-aged men (57 ± 5 years) and women (57 ± 8 years) and young men (28 ± 6 years) and women (30 ± 6 years) completed five overground running trials at a set speed of 2.7 m/s while lower limb kinematics and ground reaction forces were collected. Lower limb joint kinetics were computed, normalized to body mass and compared between age and gender groups using two-factor analyses of variance. Women reported slower average running paces than men and middle-aged runners reported slower running paces than young runners. We confirmed that young runners run with more ankle, but less hip positive work and peak positive power compared to middle-aged runners (i.e., age-related distal-to-proximal shift in joint kinetics). We also present a novel finding that women run with more ankle, but less hip peak positive power compared to men suggesting an ankle dominant strategy in women at a preferred and comfortable running pace. However, the age-related distal-to-proximal shift in joint kinetics was not different between genders.

Quantifying demands on the hamstrings during high-speed running: A systematic review and meta-analysis

INTRODUCTION

Hamstring strain injury (HSI) remains a performance, economic, and player availability burden in sport. High-speed running (HSR) is cited as a common mechanism for HSI. While evidence exists regarding the high physical demands on the hamstring muscles in HSR, meta-analytical synthesis of related activation and kinetic variables is lacking.

METHODS

A systematic search of Medline, Embase, Scopus, CINAHL, SportDiscus, and Cochrane library databases was conducted in accordance with the PRISMA 2020 guidelines. Studies reporting hamstring activation (electromyographic [EMG]) or hamstring muscle/related joint kinetics were included where healthy adult participants ran at or beyond 60% of maximum speed (activation studies) or 4 m per second (m/s) (kinetic studies).

RESULTS

A total of 96 studies met the inclusion criteria. Run intensities were categorized as "slow," "moderate," or "fast" in both activation and kinetic based studies with appropriate relative, and raw measures, respectively. Meta-analysis revealed pooled mean lateral hamstring muscle activation levels of 108.1% (95% CI: 84.4%-131.7%) of maximal voluntary isometric contraction (MVIC) during "fast" running. Meta-analysis found swing phase peak knee flexion internal moment and power at 2.2 Newton meters/kilogram (Nm/kg) (95% CI: 1.9-2.5) and 40.3 Watts/kilogram (W/kg) (95% CI: 31.4-49.2), respectively. Hip extension peak moment and power was estimated as 4.8 Nm/kg (95% CI: 3.9-5.7) and 33.1 W/kg (95% CI: 17.4-48.9), respectively.

CONCLUSIONS

As run intensity/speed increases, so do the activation and kinetic demands on the hamstrings. The presented data will enable clinicians to incorporate more objective measures into the design of injury prevention and return-to-play decision-making strategies.

The Effect of Using Marathon Shoes or Track Spikes on Neuromuscular Fatigue caused by a Long-distance Track Training Session

This study aims to compare the effect of the Nike ZoomX Dragonfly track spikes and the Nike ZoomX VaporflyNext% 2 marathon shoes on the fatigue manifestations present over and after a long-distance track training session. Thirteen highly trained athletes completed two training sessions (i. e., 9- and 3-minute time trials with complete recovery) with the aforementioned footwear models. The pace, ground contact time, and stride length were measured over the time trials, and maximal countermovement jumps were performed previously and after the training session. The results revealed that, although there was no significant interaction in the pace distribution (p≥0.072), athletes tend to be only able to increase the pace at the last lap with the marathon shoes (5.4 meters [-3.7 to 14.5 meters]) meanwhile with the track spikes it further decreased (-3.1 meters [-9.8 to 3.6 meters]). A reduced ground contact time over the session (p=0.025) and a tendency toward increasing stride length (p=0.09) in the last time trial were observed. The significant interaction on the countermovement jump height (p=0.023; Track spikes: -5.60%; Marathon shoes: 0.61%) also indicates that footwear influences the resulted allostatic load.

Influence of Body Mass on Running-Induced Changes in Mechanical Properties of Plantar Fascia

ABSTRACT

Shiotani, H, Mizokuchi, T, Yamashita, R, Naito, M, and Kawakami, Y. Influence of body mass on running-induced changes in mechanical properties of plantar fascia. J Strength Cond Res 37(11): e588-e592, 2023-Body mass is a major risk factor for plantar fasciopathy; however, evidence explaining the process between risk factors and injury development is limited. Long-distance running induces transient and site-specific reduction in plantar fascia (PF) stiffness, reflecting mechanical fatigue and microscopic damage within the tissue. As greater mechanical loads can induce greater reduction in tissue stiffness, we hypothesized that the degree of running-induced change in PF stiffness is associated with body mass. Ten long-distance male runners (age: 21 - 23 years, body mass: 55.5 ± 4.2 kg; mean ± SD ) and 10 untrained men (age: 20 - 24 years, body mass: 58.4 ± 5.6 kg) ran for 10 km. Before and immediately after running, the shear wave velocity (SWV) of PF at the proximal site, which is an index of tissue stiffness, was measured using ultrasound shear wave elastography. Although the PF SWV significantly decreased after running in runners (-4.0%, p = 0.010) and untrained men (-21.9%, p < 0.001), runners exhibited smaller changes ( p < 0.001). The relative changes in SWV significantly correlated with body mass in both runners ( r = -0.691, p = 0.027) and untrained individuals ( r = -0.723, p = 0.018). These results indicate that a larger body mass is associated with a greater reduction in PF stiffness. Our findings provide in vivo evidence of the biomechanical basis for body mass as a risk factor for plantar fasciopathy. Furthermore, group differences suggest possible factors that reduce the fatigue responses, such as adaptation enhancing the resilience of PF and running mechanics.

Effects of induced motor fatigue on walking mechanics and energetics

Lower-body robotic exoskeletons can be used to reduce the energy demand of locomotion and increase the endurance of wearers. Understanding how motor fatigue affects walking performance may lead to better exoskeleton designs to support the changing physical capacity of an individual due to motor fatigue. The purpose of this study was to investigate the effects of motor fatigue on walking mechanics and energetics. Treadmill walking with progressively increased incline gradient was used to induce motor fatigue. Twenty healthy young participants walked on an instrumented treadmill at 1.25 m/s and 0° of incline for 5 min before (PRE) and after (POST) motor fatigue. We examined lower-limb joint mechanics, metabolic cost, and the efficiency of positive mechanical work (η+work). Compared to PRE, participants had increased net metabolic power by ∼14% (p < 0.001) during POST. Participants also had increased total-limb positive mechanical power (Total P+mech) by ∼4% during POST (p < 0.001), resulting in a reduced η+work by ∼8% (p < 0.001). In addition, the positive mechanical work contribution of the lower-limb joints during POST was shifted from the ankle to the knee while the negative mechanical work contribution was shifted from the knee to the ankle (all p < 0.017). Although greater knee positive mechanical power was generated to compensate for the reduction in ankle positive power after motor fatigue, the disproportionate increase in metabolic cost resulted in a reduced walking efficiency. The findings of this study suggest that powering the ankle joint may help delay the onset of the lower-limb joint work redistribution observed during motor fatigue.

Biomechanical adaptations during exhaustive runs at 90 to 120% of peak aerobic speed

The aim of this study was to examine how running biomechanics (spatiotemporal and kinetic variables) adapt with exhaustion during treadmill runs at 90, 100, 110, and 120% of the peak aerobic speed (PS) of a maximal incremental aerobic test. Thirteen male runners performed a maximal incremental aerobic test on an instrumented treadmill to determine their PS. Biomechanical variables were evaluated at the start, mid, and end of each run until volitional exhaustion. The change of running biomechanics with fatigue was similar among the four tested speeds. Duty factor and contact and propulsion times increased with exhaustion (P ≤ 0.004; F ≥ 10.32) while flight time decreased (P = 0.02; F = 6.67) and stride frequency stayed unchanged (P = 0.97; F = 0.00). A decrease in vertical and propulsive peak forces were obtained with exhaustion (P ≤ 0.002; F ≥ 11.52). There was no change in the impact peak with exhaustion (P = 0.41; F = 1.05). For runners showing impact peaks, the number of impact peaks increased (P ≤ 0.04; [Formula: see text] ≥ 6.40) together with the vertical loading rate (P = 0.005; F = 9.61). No changes in total, external, and internal positive mechanical work was reported with exhaustion (P ≥ 0.12; F ≤ 2.32). Results suggest a tendency towards a "smoother" vertical and horizontal running pattern with exhaustion. A smoother running pattern refers to the development of protective adjustments, leading to a reduction of the load applied to the musculoskeletal system at each running step. This transition seemed continuous between the start and end of the running trials and could be adopted by the runners to decrease the muscle force level during the propulsion phase. Despite these changes with exhaustion, there were no changes in either gesture speed (no alteration of stride frequency) or positive mechanical work, advocating that runners unconsciously organize themselves to maintain a constant whole-body mechanical work output.

A Multidimensional Assessment of a Novel Adaptive Versus Traditional Passive Ankle Sprain Protection Systems

BACKGROUND

Ankle braces aim to reduce lateral ankle sprains. Next to protection, factors influencing user compliance, such as sports performance, motion restriction, and users' perceptions, are relevant for user compliance and thus injury prevention. Novel adaptive protection systems claim to change their mechanical behavior based on the intensity of motion (eg, the inversion velocity), unlike traditional passive concepts of ankle bracing.

PURPOSE

To compare the performance of a novel adaptive brace with 2 passive ankle braces while considering protection, sports performance, freedom of motion, and subjective perception.

STUDY DESIGN

Controlled laboratory study.

METHODS

The authors analyzed 1 adaptive and 2 passive (one lace-up and one rigid brace) ankle braces, worn in a low-cut, indoor sports shoe, which was also the no-brace reference condition. We performed material testing using an artificial ankle joint system at high and low inversion velocities. Further, 20 male, young, healthy team sports athletes were analyzed using 3-dimensional motion analysis in sports-related movements to address protection, sports performance, and active range of motion dimensions. Participants rated subjective comfort, stability, and restriction experienced when using the products.

RESULTS

Subjective stability rating was not different between the adaptive and passive systems. The rigid brace was superior in restricting peak inversion during the biomechanical testing compared with the passive braces. However, in the material test, the adaptive brace increased its stiffness by approximately 400% during the fast compared with the slow inversion velocities, demonstrating its adaptive behavior and similar stiffness values to passive braces. We identified minor differences in sports performance tasks. The adaptive brace improved active ankle range of motion and subjective comfort and restriction ratings.

CONCLUSION

The adaptive brace offered similar protective effects in high-velocity inversion situations to those of the passive braces while improving range of motion, comfort, and restriction rating during noninjurious motions.

CLINICAL RELEVANCE

Protection systems are only effective when used. Compared with traditional passive ankle brace technologies, the novel adaptive brace might increase user compliance by improving comfort and freedom of movement while offering similar protection in injurious situations.

Does fatigue influence joint-specific work and ground force production during the first steps of maximal acceleration?

During initial acceleration, the first steps of a maximal-effort (sprint) run often determine success or failure in the capture and evasion of an opponent, and is therefore a vital factor of success in many modern sports. However, accelerative events are commonly performed after having already run considerable distances, and the associated fatigue should impair muscle force production and thus reduce acceleration. Despite this, the effects of running-induced fatigue on our ability to accelerate as well as the running technique used to achieve it have received little attention. We recorded 3-D kinematics and ground reaction forces during the first three steps of the acceleration phase from a standing start before and after performing a high-speed, multi-directional, fatiguing run-walk protocol in well-trained running athletes who were habituated to accelerative sprinting. We found that the athletes were able to maintain their acceleration despite changing running technique, which was associated with use of a more upright posture, longer ground contact time, increased vertical ground reaction impulse, decreased hip flexion and extension velocities, and a shift in peak joint moments, power, and positive work from the hip to the knee joint; no changes were detected in ankle joint function. Thus, a compensatory increase in knee joint function alleviated the reduction in hip flexor-extensor capacity. These acute adaptations may indicate that the hip extensors (gluteal and hamstring muscle groups) were more susceptible to fatigue than the ankle and knee musculature, and may thus be a primary target for interventions promoting fatigue resistance.

Individual physiological responses to changes in shoe bending stiffness: a cluster analysis study on 96 runners

BACKGROUND

Shoe longitudinal bending stiffness is known to influence running economy (RE). Recent studies showed divergent results ranging from 3% deterioration to 3% improvement in RE when bending stiffness increases. The variability of these results highlights inter-individual differences. Thus, our purpose was to study the runner-specific metabolic responses to changes in shoe bending stiffness.

METHODS

After assessing their maximal oxygen consumption ([Formula: see text] max) and aerobic speed (MAS) during a first visit, 96 heterogeneous runners performed two treadmill 5 min runs at 75% [Formula: see text] max with two different prototypes of shoes on a second day. Prototypes differed only by their forefoot bending stiffness (17 N/mm vs. 10.4 N/mm). RE and stride kinematics were recorded during each trial. A clustering analysis was computed by comparing the measured RE and the technical measurement error of our gas exchange analyzer to identify functional groups of runners, i.e., responding similarly to footwear interventions. ANOVAs were then computed on biomechanical and morphological variables to compare the functional groups.

RESULTS

Considering the whole sample (n = 96), there was no significant difference in RE between the two conditions. Cluster 1 (n = 29) improves RE in the stiffest condition (2.7 ± 2.1%). Cluster 2 (n = 26) impairs RE in the stiffest condition (2.7 ± 1.3%). Cluster 3 (n = 41) demonstrated no change in RE (0.28 ± 0.65%). Cluster 1 demonstrated 1.7 km·h^-1 greater MAS compared to cluster 2 (p = 0.014).

CONCLUSION

The present study highlights that the effect of shoe bending stiffness on RE is runner-specific. High-level runners took advantage of increased bending stiffness, whereas medium-level runners did not. Finally, this study emphasizes the importance of individual response examination to understand the effect of footwear on runner's performance.

Quantifying and correcting for speed and stride frequency effects on running mechanics in fatiguing outdoor running

Measuring impact-related quantities in running is of interest to improve the running technique. Many quantities are typically measured in a controlled laboratory setting, even though most runners run in uncontrolled outdoor environments. While monitoring running mechanics in an uncontrolled environment, a decrease in speed or stride frequency can mask fatigue-related changes in running mechanics. Hence, this study aimed to quantify and correct the subject-specific effects of running speed and stride frequency on changes in impact-related running mechanics during a fatiguing outdoor run. Seven runners ran a competitive marathon while peak tibial acceleration and knee angles were measured with inertial measurement units. Running speed was measured through sports watches. Median values over segments of 25 strides throughout the marathon were computed and used to create subject-specific multiple linear regression models. These models predicted peak tibial acceleration, knee angles at initial contact, and maximum stance phase knee flexion based on running speed and stride frequency. Data were corrected for individual speed and stride frequency effects during the marathon. The speed and stride frequency corrected and uncorrected data were divided into ten stages to investigate the effect of marathon stage on mechanical quantities. This study showed that running speed and stride frequency explained, on average, 20%-30% of the variance in peak tibial acceleration, knee angles at initial contact, and maximum stance phase knee angles while running in an uncontrolled setting. Regression coefficients for speed and stride frequency varied strongly between subjects. Speed and stride frequency corrected peak tibial acceleration, and maximum stance phase knee flexion increased throughout the marathon. At the same time, uncorrected maximum stance phase knee angles showed no significant differences between marathon stages due to a decrease in running speed. Hence, subject-specific effects of changes in speed and stride frequency influence the interpretation of running mechanics and are relevant when monitoring, or comparing the gait pattern between runs in uncontrolled environments.

Effects of level running-induced fatigue on running kinematics: A systematic review and meta-analysis

BACKGROUND

Runners have a high risk of acquiring a running-related injury. Understanding the mechanisms of impact force attenuation into the body when a runner fatigues might give insight into the role of running kinematics on the aetiology of overuse injuries.

RESEARCH QUESTIONS

How do running kinematics change due to running-induced fatigue? And what is the influence of experience level on changes in running kinematics due to fatigue?

METHODS

Three electronic databases were searched: PubMed, Web of Science, and Scopus. This resulted in 33 articles and 19 kinematic quantities being included in this review. A quality assessment was performed on all included articles and meta-analyses were performed for 18 kinematic quantities.

RESULTS AND SIGNIFICANCE

Main findings included an increase in peak acceleration at the tibia and a decrease in leg stiffness after a fatiguing protocol. Additionally, level running-induced fatigue increased knee flexion at initial contact and maximum knee flexion during swing. An increase in vertical centre of mass displacement was found in novice but not in experienced runners with fatigue. Overall, runners changed their gait pattern due to fatigue by moving to a smoother gait pattern (i.e. more knee flexion at initial contact and during swing, decreased leg stiffness). However, these changes were not sufficient to prevent an increase in peak accelerations at the tibia after a fatigue protocol. Large inter-individual differences in responses to fatigue were reported. Hence, it is recommended to investigate changes in running kinematics as a result of fatigue on a subject-specific level since group-level analysis might mask individual responses.

Leaning the Trunk Forward Decreases Patellofemoral Joint Loading During Uneven Running

ABSTRACT

AminiAghdam, S, Epro, G, James, D, and Karamanidis, K. Leaning the trunk forward decreases patellofemoral joint loading during uneven running. J Strength Cond Res 36(12): 3345-3351, 2022-Although decline surfaces or a more upright trunk posture during running increase the patellofemoral joint (PFJ) contact force and stress, less is known about these kinetic parameters under simultaneous changes to the running posture and surface height. This study aimed to investigate the interaction between Step (10-cm drop-step and level step) and Posture (trunk angle from the vertical: self-selected, ∼15°; backward, ∼0°; forward, ∼25°) on PFJ kinetics (primary outcomes) and knee kinematics and kinetics as well as hip and ankle kinetics (secondary outcomes) in 12 runners at 3.5 ms -1 . Two-way repeated measures analyses of variance ( α = 0.05) revealed no step-related changes in peak PFJ kinetics across running postures; however, a decreased peak knee flexion angle and increased joint stiffness in the drop-step only during backward trunk-leaning. The Step main effect revealed significantly increased peak hip and ankle extension moments in the drop-step, signifying pronounced mechanical demands on these joints. The Posture main effect revealed significantly higher and lower PFJ kinetics during backward and forward trunk-leaning, respectively, when compared with the self-selected condition. Forward trunk-leaning yielded significantly lower peak knee extension moments and higher hip extension moments, whereas the opposite effects occurred with backward trunk-leaning. Overall, changes to the running posture, but not to the running surface height, influenced the PFJ kinetics. In line with the previously reported efficacy of forward trunk-leaning in mitigating PFJ stress while even or decline running, this technique, through a distal-to-proximal joint load redistribution, also seems effective during running on surfaces with height perturbations.

Positive influence of neuromuscular training on knee injury risk factors during cutting and landing tasks in elite youth female handball players

Anterior cruciate ligament (ACL) ruptures are frequent in the age group of 15–19 years, particularly for female athletes. Although injury-prevention programs effectively reduce severe knee injuries, little is known about the underlying mechanisms and changes of biomechanical risk factors. Thus, this study analyzes the effects of a neuromuscular injury-prevention program on biomechanical parameters associated with ACL injuries in elite youth female handball players. In a nonrandomized, controlled intervention study, 19 players allocated to control (n = 12) and intervention (n = 7) group were investigated for single- and double-leg landings as well as unanticipated side-cutting maneuvers before and after a 12-week study period. The lower-extremity motion of the athletes was captured using a three-dimensional motion capture system consisting of 12 infrared cameras. A lower-body marker set of 40 markers together with a rigid body model, including a forefoot, rearfoot, shank, thigh, and pelvis segment in combination with two force plates was used to determine knee joint angles, resultant external joint moments, and vertical ground reaction forces. The two groups did not differ significantly during pretesting. Only the intervention group showed significant improvements in the initial knee abduction angle during single leg landing (p = 0.038: d = 0.518), knee flexion moment during double-leg landings (p = 0.011; d = −1.086), knee abduction moment during single (p = 0.036; d = 0.585) and double-leg landing (p = 0.006; d = 0.944) and side-cutting (p = 0.015;d = 0.561) as well as vertical ground reaction force during double-leg landing (p = 0.004; d = 1.482). Control group demonstrated no significant changes in kinematics and kinetics. However, at postintervention both groups were not significantly different in any of the biomechanical outcomes except for the normalized knee flexion moment of the dominant leg during single-leg landing. This study provides first indications that the implementation of a training intervention with specific neuromuscular exercises has positive impacts on biomechanical risk factors associated with ACL injury risk and, therefore, may help prevent severe knee injuries in elite youth female handball players.

2021 ISB World Athletics Award for Biomechanics: The Subtalar Joint Maintains "Spring-Like" Function While Running in Footwear That Perturbs Foot Pronation

Humans have the remarkable ability to run over variable terrains. During locomotion, however, humans are unstable in the mediolateral direction and this instability must be controlled actively-a goal that could be achieved in more ways than one. Walking research indicates that the subtalar joint absorbs energy in early stance and returns it in late stance, an attribute that is credited to the tibialis posterior muscle-tendon unit. The purpose of this study was to determine how humans (n = 11) adapt to mediolateral perturbations induced by custom-made 3D-printed "footwear" that either enhanced or reduced pronation of the subtalar joint (modeled as motion in 3 planes) while running (3 m/s). In all conditions, the subtalar joint absorbed energy (ie, negative mechanical work) in early stance followed by an immediate return of energy (ie, positive mechanical work) in late stance, demonstrating a "spring-like" behavior. These effects increased and decreased in footwear conditions that enhanced or reduced pronation (P ≤ .05), respectively. Of the recorded muscles, the tibialis posterior (P ≤ .05) appeared to actively change its activation in concert with the changes in joint energetics. We suggest that the "spring-like" behavior of the subtalar joint may be an inherent function that enables the lower limb to respond to mediolateral instabilities during running.

Running-induced fatigue and impact loading in runners: A systematic review and meta-analysis

This systematic review and meta-analysis aimed to synthesise and clarify the effect of running-induced fatigue on impact loading during running. Eight electronic databases were systematically searched until April 2021. Studies that analysed impact loading over the course of a run, in adult runners free of medical conditions were included. Changes in leg stiffness, vertical stiffness, shock attenuation, peak tibial accelerations, peak ground reaction forces (GRF) and loading rates were extracted. Subgroup analyses were conducted depending on whether participants were required to run to exhaustion. Thirty-six studies were included in the review, 25 were included in the meta-analysis. Leg stiffness decreased with running-induced fatigue (SMD -0.31, 95% CI -0.52, -0.08, moderate evidence). Exhaustive and non-exhaustive subgroups were different for peak tibial acceleration (Chi² = 3.79, p = 0.05), with limited evidence from exhaustive subgroups showing an increase in peak tibial acceleration with fatigue. Findings for vertical GRF impact peak and peak braking force were conflicting based on exhaustive and non-exhaustive protocols (Chi² = 3.83, p = 0.05 and Chi² = 5.10, p = 0.02, respectively). Moderate evidence suggests leg stiffness during running decreases with fatigue. Given the non-linear relationship between leg stiffness and running economy, this may have implications for performance.

Changes in ankle work, foot work, and tibialis anterior activation throughout a long run

BACKGROUND

The ankle and foot together contribute to over half of the positive and negative work performed by the lower limbs during running. Yet, little is known about how foot kinetics change throughout a run. The amount of negative foot work may decrease as tibialis anterior (TA) electromyography (EMG) changes throughout longer-duration runs. Therefore, we examined ankle and foot work as well as TA EMG changes throughout a changing-speed run.

METHODS

Fourteen heel-striking subjects ran on a treadmill for 58 min. We collected ground reaction forces, motion capture, and EMG. Subjects ran at 110%, 100%, and 90% of their 10-km running speed and 2.8 m/s multiple times throughout the run. Foot work was evaluated using the distal rearfoot work, which provides a net estimate of all work contributors within the foot.

RESULTS

Positive foot work increased and positive ankle work decreased throughout the run at all speeds. At the 110% 10-km running speed, negative foot work decreased and TA EMG frequency shifted lower throughout the run. The increase in positive foot work may be attributed to increased foot joint work performed by intrinsic foot muscles. Changes in negative foot work and TA EMG frequency may indicate that the TA plays a role in negative foot work in the early stance of a run.

CONCLUSION

This study is the first to examine how the kinetic contributions of the foot change throughout a run. Future studies should investigate how increases in foot work affect running performance.

Neuromuscular, biomechanical, and energetic adjustments following repeated bouts of downhill running

PURPOSE

This study used downhill running as a model to investigate the repeated bout effect (RBE) on neuromuscular performance, running biomechanics, and metabolic cost of running.

METHODS

Ten healthy recreational male runners performed two 30-min bouts of downhill running (DR1 and DR2) at a -20% slope and 2.8 m/s 3 weeks apart. Neuromuscular fatigue, level running biomechanics during slow and fast running, and running economy parameters were recorded immediately before and after the downhill bouts, and at 24 h, 48 h, 72 h, 96 h, and 168 h thereafter (i.e., follow-up days).

RESULTS

An RBE was confirmed by attenuated muscle soreness and serum creatine kinase rise after DR2 compared to DR1. An RBE was also observed in maximum voluntary contraction (MVC) force loss and voluntary activation where DR2 resulted in attenuated MVC force loss and voluntary activation immediately after the run and during follow-up days. The downhill running protocol significantly influenced level running biomechanics; an RBE was observed in which center of mass excursion and, therefore, lower-extremity compliance were greater during follow-up days after DR1 compared to DR2. The observed changes in level running biomechanics did not influence the energy cost of running.

CONCLUSION

This study demonstrated evidence of adaptation in neural drive as well as biomechanical changes with the RBE after DR. The higher neural drive resulted in attenuated MVC force loss after the second bout. It can be concluded that the RBE after downhill running manifests as changes to global and central fatigue parameters and running biomechanics without substantially altering the energy cost of running.

Can changes in midsole bending stiffness of shoes affect the onset of joint work redistribution during a prolonged run?

PURPOSE

This study aimed to investigate if changing the midsole bending stiffness of athletic footwear can affect the onset of lower limb joint work redistribution during a prolonged run.

METHODS

Fifteen trained male runners (10-km time of <44 min) performed 10-km runs at 90% of their individual speed at lactate threshold (i.e., when change in lactate exceeded 1 mmol/L during an incremental running test) in a control and stiff shoe condition on 2 occasions. Lower limb joint kinematics and kinetics were measured using a motion capture system and a force-instrumented treadmill. Data were acquired every 500 m.

RESULTS

Prolonged running resulted in a redistribution of positive joint work from distal to proximal joints in both shoe conditions. Compared to the beginning of the run, less positive work was performed at the ankle (approximately 9%; p ≤ 0.001) and more positive work was performed at the knee joint (approximately 17%; p ≤ 0.001) at the end of the run. When running in the stiff shoe condition, the onset of joint work redistribution at the ankle and knee joints occurred at a later point during the run.

CONCLUSION

A delayed onset of joint work redistribution in the stiff condition may result in less activated muscle volume, because ankle plantar flexor muscles have shorter muscles fascicles and smaller cross-sectional areas compared to knee extensor muscles. Less active muscle volume could be related to previously reported decreases in metabolic cost when running in stiff footwear. These results contribute to the notion that footwear with increased stiffness likely results in reductions in metabolic cost by delaying joint work redistribution from distal to proximal joints.

The repeated bout effect influences lower-extremity biomechanics during a 30-min downhill run

The repeated bout effect in eccentric-biased exercises is a well-known phenomenon, wherein a second bout of exercise results in attenuated strength loss and soreness compared to the first bout. We sought to determine if the repeated bout effect influences changes in lower-extremity biomechanics over the course of a 30-min downhill run. Eleven male participants completed two bouts of 30-min downhill running (DR1 and DR2) at 2.8 m.s^-1 and -11.3° on an instrumented treadmill. Three-dimensional kinematics and ground reaction forces were recorded and used to quantify changes in spatiotemporal parameters, external work, leg stiffness, and lower extremity joint-quasi-stiffness throughout the 30-min run. Maximum voluntary isometric contraction (MVIC) and perceived quadriceps pain were assessed before-after, and throughout the run, respectively. DR2 resulted in attenuated loss of MVIC (P = 0.004), and perceived quadriceps pain (P < 0.001) compared to DR1. In general, participants ran with an increased duty factor towards the end of each running bout; however, increases in duty factor during DR2 (+5.4%) were less than during DR1 (+8.8%, P < 0.035). Significant reductions in leg stiffness (-11.7%, P = 0.002) and joint quasi-stiffness (up to -25.4%, all P < 0.001) were observed during DR1 but not during DR2. Furthermore, DR2 was associated with less energy absorption and energy generation than DR1 (P < 0.004). To summarize, the repeated bout effect significantly influenced lower-extremity biomechanics over the course of a downhill run. Although the mechanism(s) underlying these observations remain(s) speculative, strength loss and/or perceived muscle pain are likely to play a key role.HighlightsA 30-min downhill running bout increased contact time and reduced flight time transitioning to an increased duty factor.Lower-extremity stiffness also decreased and mechanical energy absorption increased over the course of the first 30-min downhill running bout.When the same bout of 30-min downhill running was performed three weeks later, the observed changes to lower extremity biomechanics were significantly attenuated.The findings from this study demonstrated, for this first time, a repeated bout effect for lower extremity biomechanics associated with downhill running.

The behaviour of T2* and T2 relaxation time in extrinsic foot muscles under continuous exercise: A prospective analysis during extended running

Objectives

Previous studies on T2* and T2 relaxation time of the muscles have shown that exercise leads to an initial increase, presumably representing different intramuscular physiological processes such as increase in intracellular volume or blood oxygenation level dependent effects with a subsequent decrease after cessation of exercise. Their behaviour during prolonged exercise is still unknown but could provide important information for example about the pathophysiology of overuse injuries. The aim of this study was to evaluate the temporal course of T2* and T2 relaxation time in extrinsic foot muscles during prolonged exercise and determine the optimal mapping technique.

Methods

Ten participants had to run a total of 75 minutes at their individual highest possible running speed, with interleaved MR scans at baseline and after 2.5, 5, 10, 15, 45 and 75 minutes. The examined extrinsic foot muscles were manually segmented, and relaxation time were analysed regarding its respective time course.

Results

T2* and T2 relaxation time showed an initial increase, followed by a plateau phase between 2.5 and 15 minutes and a subsequent decrease. For the T2* relaxation time, this pattern was also apparent, but less pronounced, with more muscles not reaching significance (p<0.05) when comparing different time points.

Conclusions

T2* and T2 relaxation time showed a similar course with an initial rapid increase, a plateau phase and a subsequent decrease under prolonged exercise. Moderate but long-term muscular activity appears to have a weaker effect on T2* relaxation time than on T2 relaxation time.

Drift-Free 3D Orientation and Displacement Estimation for Quasi-Cyclical Movements Using One Inertial Measurement Unit: Application to Running

A Drift-Free 3D Orientation and Displacement estimation method (DFOD) based on a single inertial measurement unit (IMU) is proposed and validated. Typically, body segment orientation and displacement methods rely on a constant- or zero-velocity point to correct for drift. Therefore, they are not easily applicable to more proximal segments than the foot. DFOD uses an alternative single sensor drift reduction strategy based on the quasi-cyclical nature of many human movements. DFOD assumes that the quasi-cyclical movement occurs in a quasi-2D plane and with an approximately constant cycle average velocity. DFOD is independent of a constant- or zero-velocity point, a biomechanical model, Kalman filtering or a magnetometer. DFOD reduces orientation drift by assuming a cyclical movement, and by defining a functional coordinate system with two functional axes. These axes are based on the mean acceleration and rotation axes over multiple complete gait cycles. Using this drift-free orientation estimate, the displacement of the sensor is computed by again assuming a cyclical movement. Drift in displacement is reduced by subtracting the mean value over five gait cycle from the free acceleration, velocity, and displacement. Estimated 3D sensor orientation and displacement for an IMU on the lower leg were validated with an optical motion capture system (OMCS) in four runners during constant velocity treadmill running. Root mean square errors for sensor orientation differences between DFOD and OMCS were 3.1 ± 0.4° (sagittal plane), 5.3 ± 1.1° (frontal plane), and 5.0 ± 2.1° (transversal plane). Sensor displacement differences had a root mean square error of 1.6 ± 0.2 cm (forward axis), 1.7 ± 0.6 cm (mediolateral axis), and 1.6 ± 0.2 cm (vertical axis). Hence, DFOD is a promising 3D drift-free orientation and displacement estimation method based on a single IMU in quasi-cyclical movements with many advantages over current methods.

A test of the effort equalization hypothesis in children with cerebral palsy who have an asymmetric gait

Healthy people can walk nearly effortlessly thanks to their instinctively adaptive gait patterns that tend to minimize metabolic energy consumption. However, the economy of gait is severely impaired in many neurological disorders such as stroke or cerebral palsy (CP). Moreover, self-selected asymmetry of impaired gait does not seem to unequivocally coincide with the minimal energy cost, suggesting the presence of other adaptive origins. Here, we used hemiparetic CP gait as a model to test the hypothesis that pathological asymmetric gait patterns are chosen to equalize the relative muscle efforts between the affected and unaffected limbs. We determined the relative muscle efforts for the ankle and knee extensors by relating extensor joint moments during gait to maximum moments obtained from all-out hopping reference test. During asymmetric CP gait, the unaffected limb generated greater ankle (1.36±0.15 vs 1.17±0.16 Nm/kg, p = 0.002) and knee (0.74±0.33 vs 0.44±0.19 Nm/kg, p = 0.007) extensor moments compared with the affected limb. Similarly, the maximum moment generation capacity was greater in the unaffected limb versus the affected limb (ankle extensors: 1.81±0.39 Nm/kg vs 1.51±0.34 Nm/kg, p = 0.033; knee extensors: 1.83±0.37 Nm/kg vs 1.34±0.38 Nm/kg, p = 0.021) in our force reference test. As a consequence, no differences were found in the relative efforts between unaffected and affected limb ankle extensors (77±12% vs 80±16%, p = 0.69) and knee extensors (41±17% vs 38±23%, p = 0.54). In conclusion, asymmetric CP gait resulted in similar relative muscle efforts between affected and unaffected limbs. The tendency for effort equalization may thus be an important driver of self-selected gait asymmetry patterns, and consequently advantageous for preventing fatigue of the weaker affected side musculature.

Effect of training volume on footstrike patterns over an exhaustive run

BACKGROUND

Although footstrike pattern (FP) may not be a factor influencing running performance, 11-75% of world-class distance runners use a non-rearfoot FP. However, little attention has been paid to describe the effect of running volume on FP changes when a runner is fatigued.

RESEARCH QUESTION

Does the training volume provide an adequate stimulus to mitigate FP changes during an exhaustive run in non-rearfoot, habitual minimalist footwear runners?

METHODS

The objective of this study was to compare FP between non-rearfoot, habitual minimalist footwear runners with a moderate training volume (MT) and a high training volume (HT) during an exhaustive run on a motorized treadmill. Based on their weekly training volume (distance), twenty-eight runners were arranged into two groups paired by height and age. At the first visit, runners underwent a VO2max test to acquire their velocity for the exhaustive run. During the second visit, biomechanical and physiological analysis of the beginning and the end phase of the exhaustive run was done.

RESULTS

The frontal plane foot angle, the sagittal plane ankle angle at the initial contact (IC), and the foot eversion ROM showed a significant interaction effect (P < 0.05). Additionally, the sagittal plane footstrike angle, the frontal plane foot angle, the sagittal plane ankle angle, knee flexion angle at IC and foot eversion ROM showed a significant effect of fatigue (P < 0.05). Finally, the frontal plane foot angle, the sagittal plane footstrike angle, the sagittal plane ankle angle, and the knee flexion angle showed significant group effects (P < 0.05).

SIGNIFICANCE

The training volume affects the footstrike pattern of non-rearfoot, habitual minimalist footwear runners when they are fatigued. The highly trained runners maintained their ankle angle throughout the exhaustive running protocol, whereas the moderately trained group changed the frontal and sagittal plane characteristics of their footstrike pattern.

Running-Related Biomechanical Risk Factors for Overuse Injuries in Distance Runners: A Systematic Review Considering Injury Specificity and the Potentials for Future Research

BACKGROUND

Running overuse injuries (ROIs) occur within a complex, partly injury-specific interplay between training loads and extrinsic and intrinsic risk factors. Biomechanical risk factors (BRFs) are related to the individual running style. While BRFs have been reviewed regarding general ROI risk, no systematic review has addressed BRFs for specific ROIs using a standardized methodology.

OBJECTIVE

To identify and evaluate the evidence for the most relevant BRFs for ROIs determined during running and to suggest future research directions.

DESIGN

Systematic review considering prospective and retrospective studies. (PROSPERO_ID: 236,832).

DATA SOURCES

PubMed. Connected Papers. The search was performed in February 2021.

ELIGIBILITY CRITERIA

English language. Studies on participants whose primary sport is running addressing the risk for the seven most common ROIs and at least one kinematic, kinetic (including pressure measurements), or electromyographic BRF. A BRF needed to be identified in at least one prospective or two independent retrospective studies. BRFs needed to be determined during running.

RESULTS

Sixty-six articles fulfilled our eligibility criteria. Levels of evidence for specific ROIs ranged from conflicting to moderate evidence. Running populations and methods applied varied considerably between studies. While some BRFs appeared for several ROIs, most BRFs were specific for a particular ROI. Most BRFs derived from lower-extremity joint kinematics and kinetics were located in the frontal and transverse planes of motion. Further, plantar pressure, vertical ground reaction force loading rate and free moment-related parameters were identified as kinetic BRFs.

CONCLUSION

This study offers a comprehensive overview of BRFs for the most common ROIs, which might serve as a starting point to develop ROI-specific risk profiles of individual runners. We identified limited evidence for most ROI-specific risk factors, highlighting the need for performing further high-quality studies in the future. However, consensus on data collection standards (including the quantification of workload and stress tolerance variables and the reporting of injuries) is warranted.

Effects of Fatigue Running on Joint Mechanics in Female Runners: A Prediction Study Based on a Partial Least Squares Algorithm

Background: Joint mechanics are permanently changed using different intensities and running durations. These variations in intensity and duration also influence fatigue during prolonged running. Little is known about the potential interactions between fatigue and joint mechanics in female recreational runners. Thus, the purpose of this study was to describe and examine kinematic and joint mechanical parameters when female recreational runners are subject to fatigue as a result of running.

Method: Fifty female recreational runners maintained running on a treadmill to induce fatigue conditions. Joint mechanics, sagittal joint angle, moment, and power were recorded pre- and immediately post fatigue treadmill running.

Result: Moderate reductions in absolute positive ankle power, total ankle energy dissipation, dorsiflexion at initial contact, max dorsiflexion angle, and range of motion of the joint ankle were collected after fatigue following prolonged fatigue running. Knee joint mechanics, joint angle, and joint power remained unchanged after prolonged fatigue running. Nevertheless, with the decreased ankle joint work, negative knee power increased. At the hip joint, the extension angle was significantly decreased. The range motion of the hip joint, hip positive work and hip positive power were increased during the post-prolonged fatigue running.

Conclusion: This study found no proximal shift in knee joint mechanics in amateur female runners following prolonged fatigue running. The joint work redistribution was associated with running fatigue changes. As for long-distance running, runners should include muscle strength training to avoid the occurrence of running-related injuries.

A half marathon shifts the mediolateral force distribution at the tibiofemoral joint

Runners' gait patterns vary during a half marathon and influence the knee joint mechanics. Joint contact force is a better estimate of the net joint loadings than external joint moments and closely correlates to injury risks. This study explored the changes of lower limb joint kinematics, muscle activities, and knee joint loading in runners across the running mileages of a half marathon. Fourteen runners completed a half marathon on an instrumented treadmill where motion capture was conducted every 2 km (from 2 to 20 km). A musculoskeletal model incorporating medial/lateral tibiofemoral compartments was used to process the movement data and report outcome variables at the selected distance checkpoints. Statistics showed no changes in joint angles, muscle co-contraction index, ground reaction force variables, and medial tibiofemoral contact force (p > 0.05). Knee adduction moment at 18 km was significantly lower than those at 2 km (p = 0.002, γ = 0.813) and 6 km (p = 0.001, γ = 0.663). Compared to that at 2 km, lateral tibiofemoral contact force was reduced at 18 km (p = 0.030, Hedges' g = 0.690), 16 km (p < 0.001, Hedges' g = 0.782), 14 km (p = 0.045, Hedges' g = 0.859), and 10 km (p < 0.001, Hedges' g = 0.771) respectively. Mechanical realignment of the lower limb may be the cause of the altered knee loadings and possibly led to reduced running economy in response to a prolonged run. The injury potential of the redistributed tibiofemoral forces warranted further studies.

Uneven running: How does trunk-leaning affect the lower-limb joint mechanics and energetics?

This study aimed to investigate the role of trunk posture in running locomotion. Twelve recreational runners ran in the laboratory across even and uneven ground surface (expected 10 cm drop-step) with three trunk-lean angles from the vertical (self-selected, ∼15°; anterior, ∼25°; posterior, ∼0°) while 3D kinematic and kinetic data were collected using a 3D motion-capture-system and two embedded force-plates. Two-way repeated measures ANOVAs (α = 0.05) compared lower-limb joint mechanics (angles, moments, energy absorption and generation) and ground-reaction-force parameters (braking and propulsive impulse) between Step (level and drop) and Posture conditions. The Step-by-Posture interaction revealed decreased hip energy generation, and greater peak knee extension moment in the drop-step during running with posterior versus anterior trunk-lean. Furthermore, energy absorption across hip and ankle nearly doubled in the drop-step across all running conditions. The Step main effect revealed that the knee and ankle energy absorption, ankle energy generation, ground-reaction-force, and braking impulse significantly increased in the drop-step. The Posture main effect revealed that, compared with a self-selected trunk-lean, the knee's energy absorption/generation, ankle's energy generation and the braking impulse were either retained or attenuated when leaning the trunk anteriorly. The opposite effects occurred with a posterior trunk-lean. In conclusion, while the pronounced mechanical ankle stress in drop-steps is marginally affected by posture, changing the trunk-lean reorganizes the load distribution across the knee and hip joints. Leaning the trunk anteriorly in running shifts loading from the knee to the hip not only in level running but also when coping with ground-level changes.Highlights Changing the trunk-lean when running reorganizes the load distribution across the knee and hip joints.Leaning the trunk anteriorly from a habitual trunk posture during running attenuates the mechanical stress on the knee, while the opposite effect occurs with a posterior trunk-lean, irrespective to the ground surface uniformity.The effect of posture on pronounced mechanical ankle stress in small perturbation height during running is marginal.Leaning the trunk anteriorly shifts loading from the knee to the hip not only in level running but also when coping with small perturbation height.

Running into Fatigue: The Effects of Footwear on Kinematics, Kinetics, and Energetics

PURPOSE

Recent studies identified a redistribution of positive mechanical work from distal to proximal joints during prolonged runs, which might partly explain the reduced running economy observed with running-induced fatigue. Higher mechanical demand of plantar flexor muscle-tendon units, for example, through minimal footwear, can lead to an earlier onset of fatigue, which might affect the redistribution of lower extremity joint work during prolonged runs. Therefore, the purpose of this study was to examine the effects of a racing flat and cushioned running shoe on the joint-specific contributions to lower extremity joint work during a prolonged fatiguing run.

METHODS

On different days, 18 runners performed two 10-km runs with near-maximal effort in a racing flat and a cushioned shoe on an instrumented treadmill synchronized with a motion capture system. Joint kinetics and kinematics were calculated at 13 predetermined distances throughout the run. The effects of shoes, distance, and their interaction were analyzed using a two-factor repeated-measures ANOVA.

RESULTS

For both shoes, we found a redistribution of positive joint work from the ankle (-6%) to the knee (+3%) and the hip (+3%) throughout the entire run. Negative ankle joint work was higher (P < 0.01) with the racing flat compared with the cushioned shoe. Initial differences in foot strike patterns between shoes disappeared after 2 km of running distance.

CONCLUSIONS

Irrespective of the shoe design, alterations in the running mechanics occurred in the first 2 km of the run, which might be attributed to the existence of a habituation rather than fatigue effect. Although we did not find a difference between shoes in the fatigue-related redistribution of joint work from distal to more proximal joints, more systematical studies are needed to explore the effects of specific footwear design features.

Training Load Capacity, Cumulative Risk, and Bone Stress Injuries: A Narrative Review of a Holistic Approach

Bone stress injuries (BSIs) are a common orthopedic injury with short-term, and potentially long-term, effects. Training load capacity, influenced by risk factors, plays a critical role in the occurrence of BSIs. Many factors determine how one's body responds to repetitive loads that have the potential to increase the risk of a BSI. As a scientific community, we have identified numerous isolated BSI risk factors. However, we have not adequately analyzed the integrative, holistic, and cumulative nature of the risk factors, which is essential to determine an individual's specific capacity. In this narrative review, we advocate for a personalized approach to monitor training load so that individuals can optimize their health and performance. We define “cumulative risk profile” as a subjective clinical determination of the number of risk factors with thoughtful consideration of their interaction and propose that athletes have their own cumulative risk profile that influences their capacity to withstand specific training loads. In our narrative review, we outline BSI risk factors, discuss the relationship between BSIs and training load, highlight the importance of individualizing training load, and emphasize the use of a holistic assessment as a training load guide.

Neuromechanics of Middle-Distance Running Fatigue: A Key Role of the Plantarflexors?

PURPOSE

This study aimed to investigate the changes in lower limb kinematics, kinetics, and muscle activation during a high-intensity run to fatigue (HIRF).

METHODS

Eighteen male and female competitive middle-distance runners performed a HIRF on an instrumented treadmill at a constant but unsustainable middle-distance speed (~3 min) based on a preceding maximum oxygen uptake (V˙O2max) test. Three-dimensional kinematics and kinetics were collected and compared between the start, 33%, 67%, and the end of the HIRF. In addition, the activation of eight lower limb muscles of each leg was measured with surface EMG (sEMG).

RESULTS

Time to exhaustion was 181 ± 42 s. By the end of the HIRF (i.e., vs the start), ground contact time increased (+4.0%), whereas flight time (-3.2%), peak vertical ground reaction force (-6.1%), and vertical impulse (-4.1%) decreased (all P < 0.05), and joint angles at initial contact became more (dorsi)flexed (ankle, +1.9°; knee, +2.1°; hip, +3.6°; all P < 0.05). During stance, by the end of the HIRF: peak ankle plantarflexion moment decreased by 0.4 N·m·kg-1 (-9.0%), whereas peak knee extension moment increased by 0.24 N·m·kg-1 (+10.3%); similarly, positive ankle plantarflexion work decreased by 0.19 J·kg-1 (-13.9%), whereas positive knee extension work increased by 0.09 J·kg-1 (+33.3%; both P < 0.05) with no change in positive hip extension work. Hip extensor surface EMG amplitude increased during the late swing phase (+20.9-37.3%; P < 0.05).

CONCLUSION

Running at a constant middle-distance pace led primarily to the fatigue of the plantarflexors with a compensatory increase in positive work done at the knee. Improving the fatigue resistance of the plantarflexors might be beneficial for middle-distance running performance.

Track distance runners exhibit bilateral differences in the plantar fascia stiffness

Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; however, track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress. This may induce asymmetrical adaptation in the runners’ foot arch functions, but this has not been experimentally tested. Here, we show that the plantar fascia (PF), a primary structure of the foot arch elasticity, is stiffer for the left than the right foot as a characteristic of runners, via a cross-sectional study on 10 track distance runners and 10 untrained individuals. Shear wave velocity (index of tissue stiffness: SWV) and thickness of PF and foot dimensions were compared between sides and groups. Runners showed higher PF SWV in their left (9.4 ± 1.0 m/s) than right (8.9 ± 0.9 m/s) feet, whereas untrained individuals showed no bilateral differences (8.5 ± 1.5 m/s and 8.6 ± 1.7 m/s, respectively). Additionally, runners showed higher left to right (L/R) ratio of PF SWV than untrained men (105.1% and 97.7%, respectively). PF thickness and foot dimensions were not significantly different between sides or groups. These results demonstrate stiffer PF in the left feet of runners, which may reflect adaptation to their running-specific training that involves asymmetrical mechanical loading.

Insights into extrinsic foot muscle activation during a 75 min run using T2 mapping

The extrinsic foot muscles are essentially for controlling the movement path but our knowledge of their behavior during prolonged running is still very limited. Therefore, this study analyzed the time-course of muscle activation using T2 mapping during 75 min of running. In this prospective study, 19 recreational active runners completed 75 min of treadmill running at a constant speed. Interleaved T2 mapping sequences were acquired and segmented at timepoints 0, 2.5, 5, 10, 15, 45, and 75 min. ANOVA for repeated measurements followed by a Tukey post hoc test and Pearson correlation between running speed and initial signal increase at 2.5 min were calculated. All muscles showed a significant signal increase between baseline and 2.5 min (e.g. medial gastrocnemius: + 15.48%; p < 0.01). This was followed by a plateau phase till 15 min for all but the extensor digitorum longus muscle and a significant decrease at 45 or 75 min for all muscles (all p < 0.05). Correlation between running speed and signal increase was negative for all muscles and significant for both gastrocnemii (e.g. medial: r =  - 0.57, p = 0.0104) and soleus (r =  - 0.47, p = 0.0412). The decrease of relaxation times times in the later running phases was less pronounced for faster runners (≥ 10 km/h). T2 relaxation times do not only decrease after cessation of exercise but already during prolonged running. The lesser initial increase and later decrease in faster runners may indicate training induced changes.

The effects of shoe upper construction on mechanical ankle joint work during lateral shuffle movements

Lateral shuffles are common movements in sports and are facilitated by the hip, knee, and ankle joints. Shoe uppers can change ankle kinetics during walking and running. However, it is not known how shoe upper modifications affect ankle kinetics during shuffling. The purpose of this study was to investigate the effects of shoe upper construction on mechanical ankle joint work during shuffling. It was hypothesized that a shoe with a reinforced upper will result in decreased negative ankle joint work. Twenty participants performed Maximal (MLST) and Submaximal Lateral Shuffle Tests (90% of MLST) in footwear with a minimal (MU) and reinforced upper (RU). Ground reaction forces and ankle kinematics were collected to compute ankle joint work. Performing lateral shuffles in the RU condition resulted in significantly reduced positive (MU: 0.62 ± 0.16 J/kg, RU: 0.55 ± 0.16 J/kg; p = 0.001, d = 0.44) and negative (MU: -0.60 ± 0.20 J/kg, RU: -0.53 ± 0.19 J/kg; p = 0.004, d = 0.41) ankle work. A decrease in positive and negative work could be a performance benefit, enabling the athlete to perform the same movement with a lower energy cost. More extreme upper interventions may yield even larger performance benefits.

Fatigue-Related Changes in Spatiotemporal Parameters, Joint Kinematics and Leg Stiffness in Expert Runners During a Middle-Distance Run

Fatigue with its underlying mechanisms and effects is a broadly discussed topic and an important phenomenon, particularly in endurance sports. Although several studies have already shown a variety of changes in running kinematics with fatigue, few of them have analyzed competitive runners and even fewer have focused on middle-distance running. Furthermore, the studies investigating fatigue-related changes have mostly reported the results in terms of discrete parameters [e.g., range of motion (RoM)] in the frontal or sagittal plane, and therefore potentially overlooked effects occurring in subphases of the gait cycle or in the transverse plane. On this basis, the goal of the present study was to analyze the effects of exhaustive middle-distance running on expert runners by means of both discrete parameters and time series analysis in 3D. In this study, 13 runners ran on a treadmill to voluntary exhaustion at their individually determined fatigue speeds which was held constant during the measurements. Kinematic data were collected by means of a 3D motion capture system. Spatiotemporal and stiffness parameters as well as the RoM of joints and of center of mass (CoM) within the stance and flight phases were calculated. Independent t-tests were performed to investigate any changes in means and coefficients of variation (CV) of these parameters between the rested (PRE) and fatigued (POST) state. Statistical parametric mapping method was applied on the time series data of the joints and the CoM. Results from this exploratory study revealed that during a middle-distance run, expert runners change their stance time, rather than their step frequency or step length in order to maintain the constant running speed as long as possible. Increased upper body movements occurred to counteract the increased angular moment of the lower body possibly due to longer stance times. These findings provide insights into adaptation strategies of expert runners during a fatiguing middle-distance run and may serve a valuable information particularly for comparisons with other group of runners (e.g., females or non-athletes) as well with other conditions (e.g., non-constant speed or interval training), and might be useful for the definition of training goals (e.g., functional core training).

Increasing the midsole bending stiffness of shoes alters gastrocnemius medialis muscle function during running

In recent years, increasing the midsole bending stiffness (MBS) of running shoes by embedding carbon fibre plates in the midsole resulted in many world records set during long-distance running competitions. Although several theories were introduced to unravel the mechanisms behind these performance benefits, no definitive explanation was provided so far. This study aimed to investigate how the function of the gastrocnemius medialis (GM) muscle and Achilles tendon is altered when running in shoes with increased MBS. Here, we provide the first direct evidence that the amount and velocity of GM muscle fascicle shortening is reduced when running with increased MBS. Compared to control, running in the stiffest condition at 90% of speed at lactate threshold resulted in less muscle fascicle shortening (p = 0.006, d = 0.87), slower average shortening velocity (p = 0.002, d = 0.93) and greater estimated Achilles tendon energy return (p ≤ 0.001, d = 0.96), without a significant change in GM fascicle work (p = 0.335, d = 0.40) or GM energy cost (p = 0.569, d = 0.30). The findings of this study suggest that running in stiff shoes allows the ankle plantarflexor muscle-tendon unit to continue to operate on a more favourable position of the muscle's force-length-velocity relationship by lowering muscle shortening velocity and increasing tendon energy return.

The effects of acute physical fatigue on sauté jump biomechanics in dancers

Dancers spend large amounts of time practicing and performing, where fatigue may occur, resulting in adverse movement patterns. The purpose of this study was to compare sauté landings before and after acute physical fatigue in experienced female dancers. Twenty-one dancers completed 10 sauté jumps before and after a dance-specific fatigue protocol. A 12-camera motion capture system and a force plate were utilized to collect three-dimensional kinematic and kinetic data. After fatigue, dancers demonstrated an increase in mediolateral centre of mass displacement, pelvis excursion, peak knee abduction, peak ankle eversion and external rotation, as well as decreased peak metatarsophalangeal (MTP) joint extension, indicating less desirable movement patterns. Peak vertical ground reaction force was decreased after fatigue due to a softer landing strategy, demonstrated by increased peak hip flexion, knee flexion, and ankle dorsiflexion. There was some indication of shifting demands demonstrated by an increased peak knee extensor moment and decreased peak MTP flexor moment after fatigue. With jump landing kinematics and kinetics affected after only an average of 5 minutes of dancing, dancers may benefit from developing greater endurance and more eccentric strength to allow them to slow down properly while landing and to sustain the aesthetic demands throughout performance.