Patterns of leg muscle recruitment vary between novice and highly trained cyclists

Impact of resistance and high-intensity interval training on body composition, physical function, and temporal dynamics of adaptation in older women with impaired cardiometabolic health: a randomized clinical trial

PURPOSE

Physical inactivity is associated with reduced physical fitness (PF) in older women with impaired cardiometabolic health. Although exercise has been shown to improve PF, interindividual variability in response and adaptation changes over time remain unclear. This study evaluated the effects of eight weeks of resistance training (RT) and high-intensity interval training (HIIT) on body composition, isometric strength, and the 6-minute walk test (6MWT) in older women with impaired cardiometabolic health. Additionally, the study explored the reduction of non-responders (NRs) and adaptation changes over time.

METHODS

This randomized clinical trial involved 36 older women (64 ± 8.4 years; BMI: 31.8 ± 5.5) with impaired cardiometabolic health, divided into RT-G (n = 12; 62 ± 7 years; BMI: 32.2 ± 4.1), HIIT-G (n = 12; 66 ± 10 years; BMI: 31.2 ± 4.1), and CG (n = 12; 64 ± 9 years; BMI: 31.8 ± 6) groups. RT-G performed elastic band exercises, and HIIT-G performed cycle ergometer intervals. BMI, body fat, lean mass, isometric strength, and 6MWT were measured at baseline and at four and eight weeks. The Student's t-test was applied for normally distributed variables and the Mann-Whitney U test for non-normal variables. Intra- and inter-group differences were analyzed using a two-way repeated measures ANOVA, considering group, time, and their interaction. Post-hoc comparisons were conducted using the Bonferroni test. Individual responses (IR) were calculated using the equation proposed by Hopkins: SDIR = √(SDExp2 - SDCon2). The prevalence of responders (Rs) and non-responders (NRs) was expressed as a percentage, and percentage changes from baseline to weeks four and eight were used to evaluate adaptations dynamics.

RESULTS

By week eight, isometric strength in RT-G significantly improved from 21.3 ± 4.4 to 24.37 ± 3.99 kg (p = 0.027; 95% CI: 1.8, 4.3 kg; Cohen's d = 0.731) and 6MWT distance in HIIT-G increased from 441.0 ± 48.9 to 480.0 ± 53.0 m. (p = 0.002; 95% CI: 22, 55 m; Cohen's d = 0.757). Both protocols reduced NRs for body fat, lean mass, and 6MWT. Responders showed greater adaptations in the first four weeks, stabilizing by week eight.

CONCLUSION

RT and HIIT improved PF in older women with impaired cardiometabolic health, reducing NRs in terms of body composition and 6MWT over eight weeks, with similar adaptation changes over time among the responders. These findings highlight the importance of individualized exercise interventions to maximize health benefits.

TRIAL REGISTRATION

This study was part of a trial registered at ClinicalTrials.gov (ID: NCT06201273). Date: 22/12/2023.

The Influence of Step Load Periodisation Based on Time Under Tension in Hypoxic Conditions on Hormone Concentrations and Postoperative ACL Rehabilitation of a Judo Athlete: A Case Study

The aim of this study was to determine the effect of a step load periodisation protocol for the rehabilitation of the anterior cruciate ligament (ACL) based on the variables of both the tempo of movement and time under tension (TUT) in normobaric hypoxia using a case study. Introduction: We verified the influence of variables such as time under tension (TUT) and the tempo of movement in hypoxia on the concentration of insulin-like growth factor 1 (IGF-1), growth hormone (GH), and erythropoietin (EPO). The effectiveness of the protocol also concerned variables such as peak torque of the knee flexors and extensors and maximum oxygen uptake (VO2max), as well as body composition analysis. Methods: The study used a 28-year-old judoka athlete from the national team, competing in the weight category up to 73 kg. Results: The use of short partial rest breaks between series (80s) in combination with six exercises in four series and a hypoxic environment (FiO2 = 15%) significantly increased metabolic stress, resulting in the highest increase in GH and IGF in the main phase of accumulation of the 3:1 step load. During 16 running sessions, the rehabilitated athlete achieved a significant increase in individual variables in the running test. Conclusions: The combination of a hypoxic environment combined with a periodized rehabilitation protocol can induce a number of positive hormonal, circulatory and respiratory reactions as well as positively influence muscle asymmetry, which can ultimately shorten the time it takes for an athlete to return to sport (RTS).

Task-dependent neuromuscular adaptations in low back pain: a controlled experimental study

Introduction

This study investigated the variability in lumbar neuromuscular adaptations to pain, the task dependency of pain adaptations and the effect of these adaptations on motor performance.

Methods

Twenty-four healthy participants performed isometric back extension contractions at 45° and 90° trunk flexion under pain-free and experimental low back pain conditions induced by electrical stimulation. High-density surface electromyography recorded lumbar muscle activation strategies, and force steadiness was measured using a load cell.

Results

While considerable variability in neuromuscular adaptations to lumbar pain was observed among participants, consistent patterns were found between tasks. In the 90° trunk flexion position, both sides exhibited greater magnitudes of pain adaptations for muscle activity redistribution in the mediolateral axis (p < 0.05, 86% increase) and muscle activity amplitude (p < 0.001, 183% increase) compared to the 45° trunk flexion position. A significant negative correlation was found between the magnitude of the mediolateral spatial redistribution of muscle activity and force steadiness on the left side (p = 0.045).

Discussion

These findings highlight the intricate and task-dependent nature of neuromuscular adaptations to pain within lumbar muscles, and points toward a potential trade-off between pain adaptations and performance.

From Novice to Expert: How Expertise Shapes Motor Variability in Sports Biomechanics-a Scoping Review

With expertise, athletes develop motor strategies that enhance sports performance or reduce functional costs. Motor variability is known as a relevant way to characterize these strategies in athletes with different levels of expertise. The aim of this scoping review is to gather and discuss the latest advances in the impact of expertise on motor variability during sports-related tasks. A search encompassing three databases, Medline, SportDiscus, and Academic Search Complete, was performed. Our research methodology included three core themes: motor variability, laboratory instruments, and sports. Motor variability metrics (e.g., standard deviation and approximate entropy) and laboratory instruments (e.g., motion capture system, EMG, and force plate) were compiled. Athletes' expertise was defined by the time of deliberate practice, the performance results, or the level in which they performed. Overall, 48 of the 59 included studies determined that higher-skilled athletes had lesser motor variability than lower-skilled athletes. This difference in motor variability between skill levels was present within individual athletes (intra-individual) and between athletes (inter-individual). This result was independent of the criteria used to define expertise, the type of instrumentation used, and the metrics used to quantify motor variability.

Exercise induces tissue-specific adaptations to enhance cardiometabolic health

The risk associated with multiple cancers, cardiovascular disease, diabetes, and all-cause mortality is decreased in individuals who meet the current recommendations for physical activity. Therefore, regular exercise remains a cornerstone in the prevention and treatment of non-communicable diseases. An acute bout of exercise results in the coordinated interaction between multiple tissues to meet the increased energy demand of exercise. Over time, the associated metabolic stress of each individual exercise bout provides the basis for long-term adaptations across tissues, including the cardiovascular system, skeletal muscle, adipose tissue, liver, pancreas, gut, and brain. Therefore, regular exercise is associated with a plethora of benefits throughout the whole body, including improved cardiorespiratory fitness, physical function, and glycemic control. Overall, we summarize the exercise-induced adaptations that occur within multiple tissues and how they converge to ultimately improve cardiometabolic health.

Agreement between Ventilatory Thresholds and Bilaterally Measured Vastus Lateralis Muscle Oxygen Saturation Breakpoints in Trained Cyclists: Effects of Age and Performance

This study focused on comparing metabolic thresholds derived from local muscle oxygen saturation (SmO2) signals, obtained using near-infrared spectroscopy (NIRS), with global pulmonary ventilation rates measured at the mouth. It was conducted among various Age Groups within a well-trained cyclist population. Additionally, the study examined how cycling performance characteristics impact the discrepancies between ventilatory thresholds (VTs) and SmO2 breakpoints (BPs).

METHODS

Junior (n = 18) and Senior (n = 15) cyclists underwent incremental cycling tests to assess their aerobic performance and to determine aerobic (AeT) and anaerobic (AnT) threshold characteristics through pulmonary gas exchange and changes in linearity of the vastus lateralis (VL) muscle SmO2 signals. We compared the relative power (Pkg) at ventilatory thresholds (VTs) and breakpoints (BPs) for the nondominant (ND), dominant (DO), and bilaterally averaged (Avr) SmO2 during the agreement analysis. Additionally, a 30 s sprint test was performed to estimate anaerobic performance capabilities and to assess the cyclists' phenotype, defined as the ratio of P@VT2 to the highest 5 s sprint power.

RESULTS

The Pkg@BP for Avr SmO2 had higher agreement with VT values than ND and DO. Avr SmO2 Pkg@BP1 was lower (p < 0.05) than Pkg@VT1 (mean bias: 0.12 ± 0.29 W/kg; Limits of Agreement (LOA): -0.45 to 0.68 W/kg; R2 = 0.72) and mainly among Seniors (0.21 ± 0.22 W/kg; LOA: -0.22 to 0.63 W/kg); there was no difference (p > 0.05) between Avr Pkg@BP2 and Pkg@VT2 (0.03 ± 0.22 W/kg; LOA: -0.40 to 0.45 W/kg; R2 = 0.86). The bias between two methods correlated significantly with the phenotype (r = -0.385 and r = -0.515 for AeT and AnT, respectively).

CONCLUSIONS

Two breakpoints can be defined in the NIRS-captured SmO2 signal of VL, but the agreement between the two methods at the individual level was too low for interchangeable usage of those methods in the practical training process. Older cyclists generally exhibited earlier thresholds in muscle oxygenation signals compared to systemic responses, unlike younger cyclists who showed greater variability and no significant differences in this regard in bias values between the two threshold evaluation methods with no significant difference between methods. More sprinter-type cyclists tended to have systemic VT thresholds earlier than local NIRS-derived thresholds than athletes with relatively higher aerobic abilities.

An Investigation of Surface EMG Shorts-Derived Training Load during Treadmill Running

The purpose of this study was two-fold: (1) to determine the sensitivity of the sEMG shorts-derived training load (sEMG-TL) during different running speeds; and (2) to investigate the relationship between the oxygen consumption, heart rate (HR), rating of perceived exertion (RPE), accelerometry-based PlayerLoadTM (PL), and sEMG-TL during a running maximum oxygen uptake (V˙O2max) test. The study investigated ten healthy participants. On day one, participants performed a three-speed treadmill test at 8, 10, and 12 km·h-1 for 2 min at each speed. On day two, participants performed a V˙O2max test. Analysis of variance found significant differences in sEMG-TL at all three speeds (p < 0.05). A significantly weak positive relationship between sEMG-TL and %V˙O2max (r = 0.31, p < 0.05) was established, while significantly strong relationships for 8 out of 10 participants at the individual level (r = 0.72-0.97, p < 0.05) were found. Meanwhile, the accelerometry PL was not significantly related to %V˙O2max (p > 0.05) and only demonstrated significant correlations in 3 out of 10 participants at the individual level. Therefore, the sEMG shorts-derived training load was sensitive in detecting a work rate difference of at least 2 km·h-1. sEMG-TL may be an acceptable metric for the measurement of internal loads and could potentially be used as a surrogate for oxygen consumption.

Intra-cycle analysis of muscle vibration during cycling

Cyclists are exposed for a long period to continuous vibrations. When a muscle is exposed to vibration, its efficiency decreases, the onset of fatigue occurs sooner, and the comfort of the cyclist is reduced. This study characterised the vastus lateralis (VL) soft tissue vibrations for different input frequencies and different pedalling phases. Ten cyclists were recruited to pedal at 55, 70, 85, and 100 rpm on a vibrating cycle ergometer that induced vibrations at frequencies ranging from 14.4 Hz (55 rpm) to 26.3 Hz (100 rpm). The VL vibration amplitude was quantified with a continuous wavelet transform and expressed as a function of the crank angle. The pedalling cycle was split into four phases (downstroke, backstroke, upstroke, and overstroke) to express the mean vibration amplitude and frequency of each phase. Statistical analysis depicted that VL vibration frequency increased with the pedalling cadence and that the VL was exposed to up to 50% more vibration amplitudes during the downstroke phase at a slow cadence. The increase in the pedal vibration frequency, a higher vibration transmission due to greater normal force on the pedal, and strong activation of the VL during the downstroke phase were discussed to explain these results.

EMG Amplitude-Force Relationship of Lumbar Back Muscles during Isometric Submaximal Tasks in Healthy Inactive, Endurance and Strength-Trained Subjects

Previous data suggest a correlation between the cross-sectional area of Type II muscle fibers and the degree of non-linearity of the EMG amplitude-force relationship (AFR). In this study we investigated whether the AFR of back muscles could be altered systematically by using different training modalities. We investigated 38 healthy male subjects (aged 19-31 years) who regularly performed either strength or endurance training (ST and ET, n = 13 each) or were physically inactive (controls (C), n = 12). Graded submaximal forces on the back were applied by defined forward tilts in a full-body training device. Surface EMG was measured utilizing a monopolar 4 × 4 quadratic electrode scheme in the lower back area. The polynomial AFR slopes were determined. Between-group tests revealed significant differences for ET vs. ST and C vs. ST comparisons at the medial and caudal electrode positions, but not for ET vs. C. Further, systematic main effects of the "electrode position" could be proven for ET and C groups with decreasing x² coefficients from cranial to caudal and lateral to medial. For ST, there was no systematic main effect of the "electrode position". The results point towards training-related changes to the fiber-type composition of muscles in the strength-trained participants, particularly for their paravertebral region.

Abdominal and lower extremity muscles activity and thickness in typically developing children and children with developmental delay

We investigated abdominal and lower extremity muscle activity and thickness in typically developing children and children with developmental delays. A total of 35 children participated: typically developing peers (n=13), children with hypotonia (n=10), and children with spasticity (n=12). Muscle activity and thickness were measured at rest and during activity. Electromyography was used to measure abdominal and lower extremity muscle activities, and abdominal muscle thickness was measured using ultrasonography. There was a significant difference between the groups in the activity of the rectus abdominis and quadriceps muscles at rest and during activity (P<0.05). There was a significant difference between the groups in the thickness of the external oblique and transversus abdominis muscles during activity (P<0.05). There was a significant difference between the groups in the thickness of the external oblique and internal oblique muscles in the sitting position (P<0.05). Therefore, the characteristics of muscle tone should be considered when applying interventions to children with developmental delay.

The relationship between pedal force application technique and the ability to perform supramaximal pedaling cadences

This study aimed to examine the relationship between the pedal force application technique under a specific competitive condition and the ability to perform steady-state pedaling at a supramaximal cadence during a special pedaling test. A total of 15 competitive male cyclists and 13 active, healthy men (novice cyclists, hereafter, novices) performed the pedaling technique test. The test imitated a road cycling competition condition (80% VO2 peak and a cadence of 90 rpm). Additionally, they performed a supramaximal cadence test that evaluated the ability to perform steady-state pedaling for an ultra-high cadence (range of 160–220 rpm) of 30 s stably with a 0.1 kgf. For the pedaling technique test, kinetic data were obtained by the pedal-shaped force platform at 1,000 Hz, and the pedaling technique was determined by the index of force effectiveness (IFE). For the supramaximal cadence test, kinematic data were obtained using a motion capture system at 200 Hz. The supramaximal pedaling cadence (C_max) was determined by measuring exercise time and targeted pedaling cadence. The IFE was 48.0 ± 9.7% in cyclists and 32.0 ± 5.9% in novices. The C_max was 215.5 ± 8.8 rpm in cyclists and 192.2 ± 13.0 rpm in novices. These values were significantly higher for cyclists than for novices. C_max was moderately correlated with IFE (r = 0.64). No significant correlation was observed between C_max and IFE for cyclists only; in contrast, a moderate correlation was observed between these parameters for novices only (r = 0.67). In conclusion, the pedal force application technique under a specific competitive condition is related to the ability to perform steady-state pedaling for supramaximal cadence during the test. Therefore, C_max may be able to explain pedal force application techniques without the need for expensive devices for novices.

Reliability and Variability of Lower Limb Muscle Activation as Indicators of Familiarity to Submaximal Eccentric Cycling

Submaximal eccentric (ECC) cycling exercise is commonly used in research studies. No previous study has specified the required time naïve participants take to familiarize with submaximal ECC cycling. Therefore, we designed this study to determine whether critical indicators of cycling reliability and variability stabilize during 15 min of submaximal, semi-recumbent ECC cycling (ECC cycling). Twenty-two participants, aged between 18–51 years, volunteered to complete a single experimental session. Each participant completed three peak eccentric torque protocol (PETP) tests, nine countermovement jumps and 15 min of submaximal (i.e., 10% peak power output produced during the PETP tests) ECC cycling. Muscle activation patterns were recorded from six muscles (rectus femoris, RF; vastus lateralis, VL; vastus medialis, VM; soleus, SOL; medial gastrocnemius, GM; tibialis anterior, TA), during prescribed-intensity ECC cycling, using electromyography (EMG). Minute-to-minute changes in the reliability and variability of EMG patterns were examined using intra-class correlation coefficient (ICC) and variance ratios (VR). Differences between target and actual power output were also used as an indicator of familiarization. Activation patterns for 4/6 muscles (RF, VL, VM and GM) became more consistent over the session, the RF, VL and VM increasing from moderate (ICC = 0.5–0.75) to good (ICC = 0.75–0.9) reliability by the 11th minute of cycling and the GM good reliability from the 1st minute (ICC = 0.79, ICC range = 0.70–0.88). Low variability (VR ≤ 0.40) was maintained for VL, VM and GM from the 8th, 8th and 1st minutes, respectively. We also observed a significant decrease in the difference between actual and target power output (χ214 = 30.895, p = 0.006, W = 0.105), expressed primarily between the 2nd and 3rd minute of cycling (Z = -2.677, p = 0.007). Indicators of familiarization during ECC cycling, including deviations from target power output levels and the reliability and variability of muscle activation patterns stabilized within 15 min of cycling. Based upon this data, it would be reasonable for future studies to allocate ∼ 15 min to familiarize naïve participants with a submaximal ECC cycling protocol.

A critical review of critical power

The elegant concept of a hyperbolic relationship between power, velocity, or torque and time to exhaustion has rightfully captivated the imagination and inspired extensive research for over half a century. Theoretically, the relationship's asymptote along the time axis (critical power, velocity, or torque) indicates the exercise intensity that could be maintained for extended durations, or the "heavy-severe exercise boundary". Much more than a critical mass of the extensive accumulated evidence, however, has persistently shown the determined intensity of critical power and its variants as being too high to maintain for extended periods. The extensive scientific research devoted to the topic has almost exclusively centered around its relationships with various endurance parameters and performances, as well as the identification of procedural problems and how to mitigate them. The prevalent underlying premise has been that the observed discrepancies are mainly due to experimental 'noise' and procedural inconsistencies. Consequently, little or no effort has been directed at other perspectives such as trying to elucidate physiological reasons that possibly underly and account for those discrepancies. This review, therefore, will attempt to offer a new such perspective and point out the discrepancies' likely root causes.

A Semi-recumbent Eccentric Cycle Ergometer Instrumented to Isolate Lower Limb Muscle Contractions to the Appropriate Phase of the Pedal Cycle

Eccentric (ECC) cycling is used in rehabilitation and sports conditioning settings. We present the construction and mode of operation of a custom-built semi-recumbent ECC cycle designed to limit the production of lower limb muscle activity to the phase of the pedal cycle known to produce ECC contractions. A commercially available semi-recumbent frame and seat (Monarch, 837E Semi-recumbent Bike, Sweden) were used to assemble the ergometer. An electrical drive train system was constructed using individual direct drive servo motors. To avoid active muscle activation occurring during the non-ECC pedaling phase of cycling, a “trip” mechanism was integrated into the drivetrain system using a servo-driven regenerative braking mechanism based on the monitoring of the voltage produced over and above a predetermined threshold produced by the motors. The servo drive internal (DC bus) voltage is recorded and internally monitored during opposing (OPP) and non-opposing (N-OPP) phases of the pedal cycle. To demonstrate that the cycle functions as desired and stops or “trips” when it is supposed to, we present average (of 5 trials) muscle activation patterns of the principal lower limb muscles for regular ECC pedal cycles in comparison with one pedal cycle during which the muscles activated outside the desired phase of the cycle for a sample participant. This semi-recumbent ECC cycle ergometer has the capacity to limit the occurrence of muscle contraction only to the ECC phase of cycling. It can be used to target that mode of muscle contraction more precisely in rehabilitation or training studies.

Trunk and lower extremity long-axis rotation exercise improves forward single leg jump landing neuromuscular control

BACKGROUND

Anterior cruciate ligament (ACL) injuries often involve sudden single leg loading with directional changes. Trunk and lower extremity (LE) load transfer and muscle power are directly coupled during these movements. The effect of trunk and LE long-axis rotation training on forward single leg drop jump landing and stabilization (FSLDJLS) was studied.

METHODS

Using block randomization (gender), 36 (18 men, 18 women) subjects were assigned to experimental (nine, 20 min exercise sessions) and control groups with equal subject number. Ground reaction force (1000 Hz), kinematic (60 Hz) and LE EMG (1000 Hz) data were synchronously collected. Statistical analysis compared pre- and post-test neuromuscular control mean change differences (MCD), and hip flexion-LE peak EMG % maximum volitional isometric contraction (%MVIC) (expressed as decimal equivalents), mean change difference (MCD) relationships.

RESULTS

The experimental group had greater landing knee flexion (3.5 ± 3.6° vs. -0.4 ± 3.3°, p = .002) MCD, greater dynamic LE stiffness after landing (0.09 ± 0.14 vs. -0.11 ± 0.14, p = .001) MCD, and increased gluteus maximus (GMAX) (0.20 ± 0.39%MVIC vs. -0.23 ± 0.46%MVIC, p = .006) and gluteus medius (GMED) EMG amplitude (0.22 ± 0.31 vs. -0.07 ± 0.36%MVIC, p = .018) MCD. This group also had decreased GMAX (-166.5 ± 403.6 ms vs. 89.3 ± 196 ms, p = .025), GMED (-75.9 ± 126.8 ms vs. 131.2 ± 207.1 ms, p = .002) and vastus lateralis (-109.1 ± 365 ms vs. 205.5 vs. 510 ms, p = .04) activation duration MCD. More experimental group subjects had increased landing knee flexion MCD (15/18 vs. 8/18, p = .015), increased dynamic LE stiffness MCD (15/18 vs. 2/18, p < .0001) and increased GMAX (15/18 vs. 7/18, p = .006) and GMED (17/18 vs. 10/18, p = .007) EMG amplitude MCD, and reduced GMAX (12/18 vs. 6/18, p = .046), GMED (11/18 vs. 5/18, p = .044), rectus femoris (12/18 vs. 6/18, p = .046), and vastus lateralis (13/18 vs. 7/18, p = .044) EMG activation duration MCD. Only the experimental group displayed significant relationships between landing and peak hip flexion and peak LE EMG amplitude MCD.

CONCLUSION

Increased dynamic LE stiffness, increased hip muscle EMG amplitude and decreased hip and knee muscle activation duration MCD in the experimental group suggests improved LE neuromuscular control.

Anthropometrics, flexibility and training history as determinants for bicycle configuration

Intrinsic factors such as leg length, arm length, flexibility and training history are factors that may be relevant to the optimisation of the individual bicycle configuration process. Bike fitting methods do not always take all these variables into account, and as yet there have been limited studies examining how these variables can affect the cyclist's position on the bicycle. The main aims of this study were to establish how individual anthropometrics, training history and flexibility may influence cyclists' freely chosen bicycle configuration, and to determine the full-body static flexion angles chosen by cyclists on the bicycle.

Fifty well-trained male cyclists were recruited for the study. A multivariate linear regression analysis was performed to predict the four main configurations of a bicycle (saddle height, saddle setback, handlebar reach and handlebar drop) based on individual anthropometrics, flexibility and training history. Average joint kinematic ranges for the knee (36°±7°) and elbow (19°±8°) joint supported previous recommendations. Hip (77°±5°) and shoulder (112°±7°) joint angles should be determined as true clinical joints.

Trochanteric leg length (p < 0.01), Knee Extension Angle test (p < 0.01) and mSchober test (p = 0.04) were significant predictors for determining saddle height. Hamstring flexibility can be used to predict handlebar drop (p = 0.01).

A cyclist who wishes to adopt a more aerodynamic position with an increased handlebar drop should aim to improve their hamstring flexibility.

Effect of Strength Training on Biomechanical and Neuromuscular Variables in Distance Runners: A Systematic Review and Meta-Analysis

BACKGROUND

Concurrent strength and endurance (CSE) training improves distance running performance more than endurance training alone, but the mechanisms underpinning this phenomenon are unclear. It has been hypothesised that biomechanical or neuromuscular adaptations are responsible for improvements in running performance; however, evidence on this topic has not been synthesised in a review.

OBJECTIVE

To evaluate the effect of CSE training on biomechanical and neuromuscular variables in distance runners.

METHODS

Seven electronic databases were searched from inception to November 2018 using key terms related to running and strength training. Studies were included if the following criteria were met: (1) population: 'distance' or 'endurance' runners of any training status; (2) intervention: CSE training; (3) comparator: running-only control group; (4) outcomes: at least one biomechanical or neuromuscular variable; and, (5) study design: randomised and non-randomised comparative training studies. Biomechanical and neuromuscular variables of interest included: (1) kinematic, kinetic or electromyography outcome measures captured during running; (2) lower body muscle force, strength or power outcome measures; and (3) lower body muscle-tendon stiffness outcome measures. Methodological quality and risk of bias for each study were assessed using the PEDro scale. The level of evidence for each variable was categorised according to the quantity and PEDro rating of the included studies. Between-group standardised mean differences (SMD) with 95% confidence intervals (95% CI) were calculated for studies and meta-analyses were performed to identify the pooled effect of CSE training on biomechanical and neuromuscular variables.

RESULTS

The search resulted in 1578 potentially relevant articles, of which 25 met the inclusion criteria and were included. There was strong evidence that CSE training significantly increased knee flexion (SMD 0.89 [95% CI 0.48, 1.30], p < 0.001), ankle plantarflexion (SMD 0.74 [95% CI 0.21-1.26], p = 0.006) and squat (SMD 0.63 [95% CI 0.13, 1.12], p = 0.010) strength, but not jump height, more than endurance training alone. Moderate evidence also showed that CSE training significantly increased knee extension strength (SMD 0.69 [95% CI 0.29, 1.09], p < 0.001) more than endurance training alone. There was very limited evidence reporting changes in stride parameters and no studies examined changes in biomechanical and neuromuscular variables during running.

CONCLUSIONS

Concurrent strength and endurance training improves the force-generating capacity of the ankle plantarflexors, quadriceps, hamstrings and gluteal muscles. These muscles support and propel the centre of mass and accelerate the leg during running, but there is no evidence to suggest these adaptations transfer from strength exercises to running. There is a need for research that investigates changes in biomechanical and neuromuscular variables during running to elucidate the effect of CSE training on run performance in distance runners.

Recognition of Foot-Ankle Movement Patterns in Long-Distance Runners With Different Experience Levels Using Support Vector Machines

Running practice could generate musculoskeletal adaptations that modify the body mechanics and generate different biomechanical patterns for individuals with distinct levels of experience. Therefore, the aim of this study was to investigate whether foot-ankle kinetic and kinematic patterns can be used to discriminate different levels of experience in running practice of recreational runners using a machine learning approach. Seventy-eight long-distance runners (40.7 ± 7.0 years) were classified into less experienced (n = 24), moderately experienced (n = 23), or experienced (n = 31) runners using a fuzzy classification system, based on training frequency, volume, competitions and practice time. Three-dimensional kinematics of the foot-ankle and ground reaction forces (GRF) were acquired while the subjects ran on an instrumented treadmill at a self-selected speed (9.5–10.5 km/h). The foot-ankle kinematic and kinetic time series underwent a principal component analysis for data reduction, and combined with the discrete GRF variables to serve as inputs in a support vector machine (SVM), to determine if the groups could be distinguished between them in a one-vs.-all approach. The SVM models successfully classified all experience groups with significant crossvalidated accuracy rates and strong to very strong Matthew’s correlation coefficients, based on features from the input data. Overall, foot mechanics was different according to running experience level. The main distinguishing kinematic factors for the less experienced group were a greater dorsiflexion of the first metatarsophalangeal joint and a larger plantarflexion angles between the calcaneus and metatarsals, whereas the experienced runners displayed the opposite pattern for the same joints. As for the moderately experienced runners, although they were successfully classified, they did not present a visually identifiable running pattern, and seem to be an intermediate group between the less and more experienced runners. The results of this study have the potential to assist the development of training programs targeting improvement in performance and rehabilitation protocols for preventing injuries.

Cycling Biomechanics and Its Relationship to Performance

State-of-the-art biomechanical laboratories provide a range of tools that allow precise measurements of kinematic, kinetic, motor and physiologic characteristics. Force sensors, motion capture devices and electromyographic recording measure the forces exerted at the pedal, saddle, and handlebar and the joint torques created by muscle activity. These techniques make it possible to obtain a detailed biomechanical analysis of cycling movements. However, despite the reasonable accuracy of such measures, cycling performance remains difficult to fully explain. There is an increasing demand by professionals and amateurs for various biomechanical assessment services. Most of the difficulties in understanding the link between biomechanics and performance arise because of the constraints imposed by the bicycle, human physiology and musculo-skeletal system. Recent studies have also pointed out the importance of evaluating not only output parameters, such as power output, but also intrinsic factors, such as the cyclist coordination. In this narrative review, we present various techniques allowing the assessment of a cyclist at a biomechanical level, together with elements of interpretation, and we show that it is not easy to determine whether a certain technique is optimal or not.

Strategies for improving the pedaling technique

INTRODUCTION

Pedaling technique which can be defined as the way the cyclists pedal, has been mostly studied in lab conditions from pedal force kinetic, joints kinematic, and/or muscular activity patterns because it is considered as a main factor for gross efficiency (GE). Although this method is much controversial, its quality has extensively been evaluated from the index of pedal force effectiveness (IFE), i.e. the ratio between the effective to the total pedal force. Over the last thirty years, preferred pedaling technique has been compared between the experienced cyclists and non-cyclists and also often been manipulated by instructing these subjects to improve their effective force production during the downstroke phase ("pushing"), the upstroke phase ("pulling-up") or around top and bottom dead centers ("circling").

EVIDENCE ACQUISITION

It has been shown that PREF pedaling technique is much repeatable across crank cycles in experienced cyclists than in novice cyclists. PULL involves a significant increase of IFE compared to PREF, mainly attributed to the increase of the muscular work of hip (RF) and knee flexors muscles (BF) during the upstroke. This improvement is larger in non-cyclists than in experienced cyclists but it can be optimized in the latter after a short-term training (2-4 weeks) with pedal force feedback or uncoupled cranks.

EVIDENCE SYNTHESIS

Despite that PULL enhances a lower muscular recruitment of contralateral knee extensors, GE and cycling performance variables are not significantly increased, probably due to the reversal effect of training with normal cranks and the highly robust pedaling technique of experienced cyclists. The question arises, as to whether or not, changes in pedaling technique can improve cycling efficiency if enough time is given for cyclists to adapt to a new pedaling technique.

CONCLUSIONS

Further studies should investigate the pedaling techniques in more "ecological" conditions, as there is not probably one but several pedaling techniques that could optimize cycling efficiency according to the pedaling conditions (time-trial, uphill, road, off-road and track cycling), and should also focus on the potential effects of long-term training of PULL pedaling technique on cycling efficiency and cycling performance.

Surface electromyography of the foot: A protocol for sensor placement

BACKGROUND

The use of surface EMG (sEMG) to record muscle activity is common place yet due to restrictions in technology studies on the intrinsic foot muscles have been limited or only fine wire instruments have been used.

AIM

This paper looks at the potential reliability of a sEMG protocol for assessing the intrinsic foot muscles.

METHODS

Six intrinsic muscles were defined using ultrasound and muscle function testing. A protocol for sensor placement was created with repeatability and reliability testing of the protocol conducted by three separate testers on three subjects over two different time frames. Inter tester and Inter session repeatability and reliability was measured with ICC and percentage standard error of measurement.

RESULTS

Although there was good correlation between Extensor Digitorum Brevis, Dorsal Interossei, Abductor Digiti Minimi and Flexor Digitorum Brevis there was increased variability and poor correlation for Flexor hallucis Brevis and Abductor Hallucis. The percentage standard error of measurement did not support the high ICC values indicating a lower precision of measurement.

SIGNIFICANCE

Variability between testers and sessions shows an inconsistent reliability of sEMG and further work is required with protocols focussing on grouping muscles to improve the understanding of the intrinsic foot muscles.

Medial Gastrocnemius Muscle Activity during Single-Leg Hopping to Exhaustion

This study described changes in leg muscle activation characteristics during exhaustive single-leg hopping. Twenty-seven healthy men performed trials (132 hops/min) to exhaustion, without a target height, to a target height with visual feedback and target height with tactile feedback. Mean muscle activation amplitude of the medial gastrocnemius (MG) decreased during the anticipatory period while duration of MG activity was maintained when hopping to a target height and contrasted the changes during hopping without a target height. Changes to MG activity were specific to whether the hopping height had been maintained or not. Changes during the anticipatory period of MG activity, indicative of adaptation in descending motor pathways, implicate utility of a motor learning strategy to allow completion of an exhaustive task.

Sprint interval exercise versus continuous moderate intensity exercise: acute effects on tissue oxygenation, blood pressure and enjoyment in 18-30 year old inactive men

BACKGROUND

Sprint interval training (SIT) can be as effective, or more effective, than continuous moderate intensity exercise (CMIE) for improving a primary risk factor for cardiometabolic disease, low cardiorespiratory fitness (CRF). However, there has been no direct comparison in inactive individuals, of the acute effects of a session of SIT with a work-matched session of CMIE on local oxygen utilisation, which is a primary stimulus for increasing CRF. Furthermore, post-exercise blood pressure (BP) and enjoyment, if symptomatic and low, respectively, have implications for safety and adherence to exercise and have not been compared between these specific conditions. It was hypothesised that in young inactive men, local oxygen utilisation would be higher, while post-exercise BP and enjoyment would be lower for SIT, when compared to CMIE.

METHODS

A total of 11 inactive men (mean ± SD; age 23 ± 4 years) completed a maximal ramp-incremental exercise test followed by two experiment conditions: (1) SIT and (2) work-matched CMIE on a cycle ergometer on separate days. Deoxygenated haemoglobin (∆HHb) in the pre-frontal cortex (FH), gastrocnemius (GN), left vastus lateralis (LVL) and the right vastus lateralis (RVL) muscles, systemic oxygen utilisation (VO2), systolic (SBP) and diastolic (DBP) blood pressure and physical activity enjoyment scale (PACES) were measured during the experiment conditions.

RESULTS

During SIT, compared to CMIE, ∆HHb in FH (p = 0.016) and GN (p = 0.001) was higher, while PACES (p = 0.032) and DBP (p = 0.043) were lower. No differences in SBP and ∆HHb in LVL and RVL were found between conditions.

CONCLUSIONS

In young inactive men, higher levels of physiological stress occurred during SIT, which potentially contributed to lower levels of post-exercise DBP and enjoyment, when compared to CMIE.

Joint specific power production in cycling: The effect of cadence and intensity

Background

The effect of cadence and work rate on the joint specific power production in cycling has previously been studied, but research has primarily focused on cadences above 60 rpm, without examining the effect of low cadence on joint contribution to power.

Purpose

Our purpose was to investigate joint specific power production in recreational and elite cyclists during low- and moderate cycling at a range of different cadences.

Methods

18 male cyclists (30.9 ± 2.7 years with a work rate in watt at lactate threshold of 282.3 ± 9.3 W) performed cycling bouts at seven different pedalling rates and three intensities. Joint specific power was calculated from kinematic measurements and pedal forces using inverse dynamics at a total of 21 different stages.

Results

A main effect of cadence on the relative to the total joint power for hip-, knee- and ankle joint power was found (all p < 0.05). Increasing cadence led to increasing knee joint power and decreasing hip joint power (all p < 0.05), with the exception at low cadence (<60 rpm), where there was no effect of cadence. The elite cyclists had higher relative hip joint power compared to the recreational group (p < 0.05). The hip joint power at moderate intensity with a freely chosen cadence (FCC) was lower than the hip joint power at low intensity with a low cadence (<60 rpm) (p < 0.05).

Conclusion

This study demonstrates that there is an effect of cadence on the hip- and knee joint contribution in cycling, however, the effect only occurs from 60 rpm and upward. It also demonstrates that there is a difference in joint contribution between elite- and recreational cyclists, and provide evidence for the possibility of achieving higher relative hip joint power at low intensity than moderate intensity by altering the cadence.

An electromyographic study of abdominal muscle activity in children with spastic cerebral palsy

Background

Inadequate knowledge in the recruitment patterns of abdominal muscles in individuals with spastic-type cerebral palsy (STCP).

Objectives

To determine whether there is any difference between the neuromuscular activity (activation pattern) of the abdominal muscles in children with STCP and those of their typically developing (TD) peers.

Method

The NORAXAN^® electromyography (EMG) was used to monitor the neuromuscular activity in abdominal muscles of individuals with STCP (n = 63), and the results were compared with the findings from age-matched TD individuals (n = 82).

Results

EMG frequencies were recorded during rest and during active states and compared using repeated measures ANOVA. Spearman's rank order correlation was used to explore relationships between age, body mass index and abdominal muscle activity. With the exception of the rectus abdominis (RA) muscle, the pattern of neuromuscular activity in children with STCP differs significantly from that of their TD peers. Three of the muscles - external oblique abdominis (EO), internal oblique abdominis (IO) and RA - in both groups showed significant changes (p < 0.001) in the frequency of EMG activity between the resting and active states. An elevated EMG activity at rest in the EO and IO was recorded in the STCP group, whereas the RA during resting and active stages showed similar results to TD individuals.

Conclusion

The findings from this study suggest that the RA could be targeted during rehabilitation regimens; however, the force generated by this muscle may not be sufficient for the maintenance of trunk stability without optimal support from the EO and IO muscles.

Effect of increasing workload on knee extensor and flexor muscular activity during cycling as measured with intramuscular electromyography

The purpose of this study was to describe the effect of increasing workload on individual thigh muscle activation during a 20 minute incremental cycling test. Intramuscular electromyographic signals were recorded from the knee extensors rectus femoris, vastus lateralis, vastus medialis and vastus intermedius and the knee flexors semimembranosus, semitendinosus, and the short and long heads of the biceps femoris during increasing workloads. Mean activation levels were compared over the whole pedaling cycle and the crank angles at which onset and offset of activation and peak activity occurred were identified for each muscle. These data were compared between three workloads. EMG activation level significantly increased (p<0.05) with increasing workload in the rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, biceps femoris long head, semitendinosus and semimembranosus but not in the biceps femoris short head. A significant change in activation timing was found for the rectus femoris, vastus lateralis, vastus medialis and semitendinosus. Of the knee flexors only the short head of the biceps femoris had its peak activity during the upstroke phase at the two highest workloads indicating a unique contribution to knee flexion.

Surface electromyographic evaluation of the neuromuscular activation of the inspiratory muscles during progressively increased inspiratory flow under inspiratory-resistive loading

This study aimed to evaluate neuromuscular activation in the scalene and sternocleidomastoid muscles using surface electromyography (EMG) during progressively increased inspiratory flow, produced by increasing the respiratory rate under inspiratory-resistive loading using a mask ventilator. Moreover, we attempted to identify the EMG inflection point (EMG^IP) on the graph, at which the root mean square (RMS) of the EMG signal values of the inspiratory muscles against the inspiratory flow velocity acceleration abruptly increases, similarly to the EMG anaerobic threshold (EMG^AT) reported during incremental-resistive loading in other skeletal muscles. We measured neuromuscular activation of healthy male subjects and found that the inspiratory flow velocity increased by approximately 1.6-fold. We successfully observed an increase in RMS that corresponded to inspiratory flow acceleration with ρ ≥ 0.7 (Spearman's rank correlation) in 17 of 27 subjects who completed the experimental protocol. To identify EMG^IP, we analyzed the fitting to either a straight or non-straight line related to the increasing inspiratory flow and RMS using piecewise linear spline functions. As a result, EMG^IP was identified in the scalene and sternocleidomastoid muscles of 17 subjects. We believe that the identification of EMG^IP in this study infers the existence of EMG^AT in inspiratory muscles. Application of surface EMG, followed by identification of EMG^IP, for evaluating the neuromuscular activation of respiratory muscles may be allowed to estimate the signs of the respiratory failure, including labored respiration, objectively and non-invasively accompanied using accessory muscles in clinical respiratory care.

Adaptations to Endurance and Strength Training

The capacity for human exercise performance can be enhanced with prolonged exercise training, whether it is endurance- or strength-based. The ability to adapt through exercise training allows individuals to perform at the height of their sporting event and/or maintain peak physical condition throughout the life span. Our continued drive to understand how to prescribe exercise to maximize health and/or performance outcomes means that our knowledge of the adaptations that occur as a result of exercise continues to evolve. This review will focus on current and new insights into endurance and strength-training adaptations and will highlight important questions that remain as far as how we adapt to training.

Do relevant shear forces appear in isokinetic shoulder testing to be implemented in biomechanical models?

Isokinetic dynamometers measure joint torques about a single fixed rotational axis. Previous studies yet suggested that muscles produce both tangential and radial forces during a movement, so that the contact forces exerted to perform this movement are multidirectional. Then, isokinetic dynamometers might neglect the torque components about the two other Euclidean space axes. Our objective was to experimentally quantify the shear forces impact on the overall shoulder torque, by comparing the dynamometer torque to the torque computed from the contact forces at the hand and elbow. Ten healthy women performed isokinetic maximal internal/external concentric/eccentric shoulder rotation movements. The hand and elbow contact forces were measured using two six-axis force sensors. The main finding is that the contact forces at the hand were not purely tangential to the direction of the movement (effectiveness indexes from 0.26 ± 0.25 to 0.54 ± 0.20), such that the resulting shoulder torque computed from the two force sensors was three-dimensional. Therefore, the flexion and abduction components of the shoulder torque measured by the isokinetic dynamometer were significantly underestimated (up to 94.9%). These findings suggest that musculoskeletal models parameters should not be estimated without accounting for the torques about the three space axes.

[Short-term exercise-based cardiac rehabilitation induced changes in cardiorespiratory, mechanical and neuromuscular responses to progressive exercise testing]

Previous studies showed that changes in peak of oxygen uptake value (VO_2peak) with training were poorly related to changes in Maximal Tolerated Power output (MTP) among patients with cardiovascular disease. This result could be due to a difference between cardiopulmonary adaptation to training and the skeletal muscle conditioning.

OBJECTIVE

The aim of the study was to compare the responses to exercise training of electromyographic activities of vastus lateralis (rms-EMG) and respiratory parameters.

METHODS

Nine cardiac patients (64.0±3.1y, 172.9±4.8cm, 83.4±16.3kg, BMI: 27.8±4.5) performed an incremental cycling exercise test to determine MTP, VO_2peak and peak values of heart rate, before and after an aerobic training. Ventilatory thresholds were respectively determined as the breakpoint in the curve of carbon dioxide output against oxygen uptake plot (VT₁) and the point at which the ratio of minute ventilation to carbon dioxide output starts to increase (VT₂). EMG_th1 and EMG_th2 were defined as the first and the second breakpoints in the rms-EMG - power output relationship.

RESULTS

Short-term exercise training (23.7±8.8 days) induced a significant increase in VO_2peak (P=0.004), MTP (P=0.015), VT₁ (P=0.001) and VT₂ (P=0.001). Changes in VO_2peak only attained the survival criteria (3.5±2.9mLmin^-1kg^-1). No significant differences (P>0.05) existed between mean power values of VT₁ and EMG_th1 (60.5±4.1 vs. 59.2±9.6% of MTP, respectively), or between VT₂ and EMG_th2 (78.3±5.7 vs. 80.2±5.2% of MTP). After training, EMG_th1 occurred significantly before VT₁ (60.5±6.2 vs. 64.8±4.8% of MTP, P=0.049).

CONCLUSION

This might be taken into account for prescribing exercise rehabilitation according initial clinical limitations of patients.

Intensity-Dependent Contribution of Neuromuscular Fatigue after Constant-Load Cycling

PURPOSE

We tested the hypothesis that central and peripheral fatigue after constant-load cycling exercise would vary with exercise intensity and duration.

METHODS

Twelve well-trained male cyclists (V˙O2max, 4.49 ± 0.35 L·min) completed three constant-load cycling trials to the limit of tolerance in a randomized crossover design. Exercise intensities were set according to the respiratory responses to a preliminary ramp test to elicit cardiorespiratory and metabolic responses consistent with exercise in the severe and heavy exercise domains: 1) at power at V˙O2max (S+, 379 ± 31 W), 2) at 60% of the difference between gas exchange threshold and V˙O2max (S-, 305 ± 23 W), and 3) at the respiratory compensation point (RCP, 254 ± 26 W). Pre- and postexercise twitch responses from the quadriceps to the electrical stimulation of the femoral nerve and magnetic stimulation of the motor cortex were recorded to assess neuromuscular and corticospinal function, respectively.

RESULTS

Exercise time was 3.14 ± 0.59, 11.11 ± 1.86, and 42.14 ± 9.09 min for S+, S-, and RCP, respectively. All trials resulted in similar reductions in maximum voluntary force (P = 0.61). However, the degree of peripheral fatigue varied in an intensity-dependent manner, with greater reductions in potentiated twitch force after S+ (-33% ± 9%) compared with both S- (-16% ± 9%, P < 0.001) and RCP trials (-11% ± 9%, P < 0.001) and greater after S- compared with RCP (P < 0.05). For central fatigue, this trend was reversed, with smaller reductions in voluntary activation after S+ compared with RCP (-2.7% ± 2.2% vs -9.0% ± 4.7%, P < 0.01).

CONCLUSION

These data suggest the magnitude of peripheral and central fatigue after locomotor cycling exercise is exacerbated with exercise intensity and duration, respectively.

Assessing experience in the deliberate practice of running using a fuzzy decision-support system

The judgement of skill experience and its levels is ambiguous though it is crucial for decision-making in sport sciences studies. We developed a fuzzy decision support system to classify experience of non-elite distance runners. Two Mamdani subsystems were developed based on expert running coaches' knowledge. In the first subsystem, the linguistic variables of training frequency and volume were combined and the output defined the quality of running practice. The second subsystem yielded the level of running experience from the combination of the first subsystem output with the number of competitions and practice time. The model results were highly consistent with the judgment of three expert running coaches (r>0.88, p<0.001) and also with five other expert running coaches (r>0.86, p<0.001). From the expert's knowledge and the fuzzy model, running experience is beyond the so-called "10-year rule" and depends not only on practice time, but on the quality of practice (training volume and frequency) and participation in competitions. The fuzzy rule-based model was very reliable, valid, deals with the marked ambiguities inherent in the judgment of experience and has potential applications in research, sports training, and clinical settings.

Adjustments with running speed reveal neuromuscular adaptations during landing associated with high mileage running training

It remains to be determined whether running training influences the amplitude of lower limb muscle activations before and during the first half of stance and whether such changes are associated with joint stiffness regulation and usage of stored energy from tendons. Therefore, the aim of this study was to investigate neuromuscular and movement adaptations before and during landing in response to running training across a range of speeds. Two groups of high mileage (HM; >45 km/wk, n = 13) and low mileage (LM; <15 km/wk, n = 13) runners ran at four speeds (2.5-5.5 m/s) while lower limb mechanics and electromyography of the thigh muscles were collected. There were few differences in prelanding activation levels, but HM runners displayed lower activations of the rectus femoris, vastus medialis, and semitendinosus muscles postlanding, and these differences increased with running speed. HM runners also demonstrated higher initial knee stiffness during the impact phase compared with LM runners, which was associated with an earlier peak knee flexion velocity, and both were relatively unchanged by running speed. In contrast, LM runners had higher knee stiffness during the slightly later weight acceptance phase and the disparity was amplified with increases in speed. It was concluded that initial knee joint stiffness might predominantly be governed by tendon stiffness rather than muscular activations before landing. Estimated elastic work about the ankle was found to be higher in the HM runners, which might play a role in reducing weight acceptance phase muscle activation levels and improve muscle activation efficiency with running training.NEW & NOTEWORTHY Although neuromuscular factors play a key role during running, the influence of high mileage training on neuromuscular function has been poorly studied, especially in relation to running speed. This study is the first to demonstrate changes in neuromuscular conditioning with high mileage training, mainly characterized by lower thigh muscle activation after touch down, higher initial knee stiffness, and greater estimates of energy return, with adaptations being increasingly evident at faster running speeds.

Use of the Wattbike Cycle Ergometer for Attenuation of Bilateral Pedaling Asymmetry in Trained Cyclists

Kell, DT and Greer, BK. Use of the Wattbike cycle ergometer for attenuation of bilateral pedaling asymmetry in trained cyclists. J Strength Cond Res 31(2): 468-473, 2017-Experienced cyclists typically pedal with a 5-20% bilateral asymmetry in regards to power output. The aim of this study was to determine if visual feedback (VF) through the Wattbike cycle ergometer is an effective tool in reducing bilateral pedaling asymmetry in trained cyclists. Twelve subjects completed three 10-minute cycling trials on the Wattbike at a power output consistent with 60% V[Combining Dot Above]O2 peak. The 3 trials consisted of a baseline (BASE) trial in which cyclists pedaled without instruction, a conscious control (CC) trial during which cyclists attempted to pedal symmetrically, and another trial in which cyclists attempted to pedal symmetrically while using VF of their bilateral power outputs (%) through the Wattbike. Although the BASE trial was always performed first, the order of the CC and VF trials was counterbalanced to minimize the influence of the order effect. For the primary analysis, the Asymmetry Index percentages (AI%s) for the 3 trials were not significantly different (p > 0.05). However, secondary analysis of subjects who had baseline AI%s within the normal, reported range showed significantly decreased AI%s during the VF trial as compared with BASE (p ≤ 0.05). These results suggest that cyclists with normal AI%s can pedal more symmetrically while using VF of their asymmetry as opposed to merely attempting conscious correction without feedback. It is currently unknown whether adopting a more bilaterally symmetrical pedaling style will improve cycling performance or decrease injury rates in cyclists.

Can muscle coordination explain the advantage of using the standing position during intense cycling?

OBJECTIVES

When compared to seated, the standing position allows the production of higher power outputs during intense cycling. We hypothesized that muscle coordination could explain this advantage. To test this hypothesis, we assessed muscle activity over a wide range of power outputs for both seated and standing cycling positions.

DESIGN

Nine lower limb muscle activities from seventeen untrained volunteers were recorded during cycling sequences performed in the seated and the standing positions at power outputs ranging from ∼100 to 700W at 90±5 revolutions-per-minute (RPM).

METHODS

Integrated electromyography activity (iEMG), temporal patterns of the EMGs, and muscle synergies were analyzed.

RESULTS

Muscle activity was underlain by four muscle synergies in both positions. Muscle synergies were similar in the two positions (Pearson's r=0.929±0.125). The activation patterns of knee and ankle extensor muscles and their associated synergies had different timings in the two positions (differences of ∼2-10% of cycle). No major timing changes were observed with power output (<2% of cycle). Differences in iEMG between the two positions depended strongly on power output in all but the calf muscle (medial gastrocnemius).

CONCLUSIONS

The number and structure of the muscle synergies play a minor role in the advantage of using the standing position when cycling at high power-outputs. However, the standing position is favorable in terms of iEMG at power outputs ≳500-600W due to position-dependent modulations of muscle activation levels. These data are important for understanding the determinants of the seat-stand transition in cycling.

Quadriceps and hamstring muscle activity during cycling as measured with intramuscular electromyography

Purpose

The aim of this study was to describe thigh muscle activation during cycling using intramuscular electromyographic recordings of eight thigh muscles, including the biceps femoris short head (BFS) and the vastus intermedius (Vint).

Methods

Nine experienced cyclists performed an incremental test (start at 170 W and increased by 20 W every 2 min) on a bicycle ergometer either for a maximum of 20 min or to fatigue. Intramuscular electromyography (EMG) of eight muscles and kinematic data of the right lower limb were recorded during the last 20 s in the second workload (190 W). EMG data were normalized to the peak activity occurring during this workload. Statistical significance was assumed at p ≤ 0.05.

Results

The vastii showed a greater activation during the 1st quadrant compared to other quadrants. The rectus femoris (RF) showed a similar activation, but with two bursts in the 1st and 4th quadrants in three subjects. This behavior may be explained by the bi-articular function during the cycling movement. Both the BFS and Vint were activated longer than, but in synergy with their respective agonistic superficial muscles.

Conclusion

Intramuscular EMG was used to verify muscle activation during cycling. The activation pattern of deep muscles (Vint and BFS) could, therefore, be described and compared to that of the more superficial muscles. The complex coordination of quadriceps and hamstring muscles during cycling was described in detail.

Trunk muscle amplitude-force relationship is only quantitatively influenced by control strategy

The Surface EMG (SEMG) amplitude-force relationship of trunk muscles has been shown to be non-linear for the abdominal muscles and linear for the back muscles. Recent studies could prove that abdominal muscles' stress level is influenced by control strategy with higher amplitude levels when the trunk posture has to be maintained along its body axis at defined submaximal force levels (posture-controlled), meanwhile compensating corresponding force levels against a fixed resistance point (force-controlled) in upright position caused inferior amplitude alterations. We wanted to check if the different control strategies alter the amplitude-force relationship of trunk muscles quantitatively and/or qualitatively. In this study 39 healthy subjects of both sexes were investigated while being isometrically exposed to defined submaximal flexion and extension forces on their trunk. The forces were generated by applying real (posture-controlled) and simulated (force-controlled) tilt angles on the trunk. SEMG was taken from five trunk muscles and normalized according to the amplitude during maximum voluntary contractions (MVC normalized), and to the occurring maximum value during every force direction and strategy, respectively (maximum normalized). The MVC normalized amplitudes were always greater for the posture-controlled situations for all abdominal muscles, independent of sex, but were not affected at all for the back muscles. The maximum normalized amplitudes of all trunk muscles were not systematically influenced by the applied control strategy. Therefore, the amplitude-force relationship of trunk muscles is muscle and exercise type-specific: for the abdominal muscles the amplitude-force relationship is quantitatively altered by control strategy.

Locomotor muscle fatigue is not critically regulated after prior upper body exercise

This study examined the effects of prior upper body exercise on subsequent high-intensity cycling exercise tolerance and associated changes in neuromuscular function and perceptual responses. Eight men performed three fixed work-rate (85% peak power) cycling tests: 1) to the limit of tolerance (CYC); 2) to the limit of tolerance after prior high-intensity arm-cranking exercise (ARM-CYC); and 3) without prior exercise and for an equal duration as ARM-CYC (ISOTIME). Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force during supramaximal electrical femoral nerve stimulation. Voluntary activation was assessed using twitch interpolation during maximal voluntary contractions. Cycling time during ARM-CYC and ISOTIME (4.33 ± 1.10 min) was 38% shorter than during CYC (7.46 ± 2.79 min) (P < 0.001). Twitch force decreased more after CYC (-38 ± 13%) than ARM-CYC (-26 ± 10%) (P = 0.004) and ISOTIME (-24 ± 10%) (P = 0.003). Voluntary activation was 94 ± 5% at rest and decreased after CYC (89 ± 9%, P = 0.012) and ARM-CYC (91 ± 8%, P = 0.047). Rating of perceived exertion for limb discomfort increased more quickly during cycling in ARM-CYC [1.83 ± 0.46 arbitrary units (AU)/min] than CYC (1.10 ± 0.38 AU/min, P = 0.003) and ISOTIME (1.05 ± 0.43 AU/min, P = 0.002), and this was correlated with the reduced cycling time in ARM-CYC (r = -0.72, P = 0.045). In conclusion, cycling exercise tolerance after prior upper body exercise is potentially mediated by central fatigue and intolerable levels of sensory perception rather than a critical peripheral fatigue limit.

Comparative Electromyography Analysis of the Upper Extremity between Inexperienced and Elite Water Polo Players during an Overhead Shot

The aim of this study was to compare muscle activity patterns between inexperienced and experienced water polo players while taking an overhead shot. The study was carried out with a group of 12 water polo players and an inexperienced group of 10 healthy participants. Signals were recorded by surface electromyography from six different muscles. The average and standard deviation of the normalized electrical activity, time to peak, time broadness, and muscle sequencing during the overhead shot were determined for each muscle in both groups and compared with each other. In water polo players, the normalized electrical activities of triceps brachii, pectoralis major, and wrist flexors were greater than other muscles, while in the inexperienced group the triceps brachii specifically played an important role. There was minimal activation of the middle deltoid and biceps brachii in water polo players. Increased times to peak and time broadness of muscles were found in the inexperienced group compared to experienced water polo players; this difference may be explained by different neuromuscular proprioception. Only experienced water polo players activated the observed muscles in a specific sequence, from proximal to distal. Therefore, coaches should emphasize smooth and quick transitions from proximal to distal segments, with less importance placed on individual muscle strengthening.

Running economy: measurement, norms, and determining factors

Running economy (RE) is considered an important physiological measure for endurance athletes, especially distance runners. This review considers 1) how RE is defined and measured and 2) physiological and biomechanical factors that determine or influence RE. It is difficult to accurately ascertain what is good, average, and poor RE between athletes and studies due to variation in protocols, gas-analysis systems, and data averaging techniques. However, representative RE values for different caliber of male and female runners can be identified from existing literature with mostly clear delineations in oxygen uptake across a range of speeds in moderately and highly trained and elite runners. Despite being simple to measure and acceptably reliable, it is evident that RE is a complex, multifactorial concept that reflects the integrated composite of a variety of metabolic, cardiorespiratory, biomechanical and neuromuscular characteristics that are unique to the individual. Metabolic efficiency refers to the utilization of available energy to facilitate optimal performance, whereas cardiopulmonary efficiency refers to a reduced work output for the processes related to oxygen transport and utilization. Biomechanical and neuromuscular characteristics refer to the interaction between the neural and musculoskeletal systems and their ability to convert power output into translocation and therefore performance. Of the numerous metabolic, cardiopulmonary, biomechanical and neuromuscular characteristics contributing to RE, many of these are able to adapt through training or other interventions resulting in improved RE.

High cycling cadence reduces carbohydrate oxidation at given low intensity metabolic rate

Cycling cadence (RPM)-related differences in blood lactate concentration (BLC) increase with increasing exercise intensity, whilst corresponding divergences in oxygen uptake (V.O₂) and carbon dioxide production (V.CO₂) decrease. Aim of the present study was to test whether a higher RPM reduces the fraction (%) of the V.O₂ used for carbohydrate oxidation (relCHO) at a given BLC. Eight males (23.9 ± 1.6 yrs; 177 ± 3 cm; 70.3 ± 3.4 kg) performed incremental load tests at 50 and 100 RPM. BLC, V.O₂ and V.CO₂ were measured. At respiratory exchange ratios (RER) < 1, relCHO were calculated and the constant determining 50 % relCHO (k_CHO) was approximated as a function of the BLC. At submaximal workload V.O₂, V.CO₂, and relCHO were lower (all p < 0.002; η² > 0.209) at 50 than at 100 RPM. No differences were observed in V.O₂peak (3.96 ± 0.22 vs. 4.00 ± 0.25 l · min⁻¹) and RER_peak (1.18 ± 0.02 vs. 1.15 ± 0.02). BLC was lower (p < 0.001; η² = 0.680) at 50 than at 100 RPM irrespective of cycling intensity. At 50 RPM, kCHO (4.2 ± 1.4 (mmol · l⁻¹)³) was lower (p = 0.043; η² = 0.466) than at 100 RPM (5.9 ± 1.9 (mmol · l⁻¹)³). This difference in k_CHO reflects a reduced CHO oxidation at a given BLC at 100 than at 50 RPM. At a low exercise intensity, a higher cycling cadence can substantially reduce the reliance on CHO at a given metabolic rate and/or BLC.

Acute effects of small changes in bicycle saddle height on gross efficiency and lower limb kinematics

The aim of the present study was to assess the acute effects of small changes in bicycle saddle height on gross efficiency (GE) and lower-limb kinematics. Well-trained cyclists (n = 14) performed a submaximal pedaling test (~70-75% of the v[Combining Dot Above]O2max) at constant cadence (90 rpm). It consisted of 3 randomized sets of 6 minutes with the preferred saddle height, 2% higher and 2% lower. Gross efficiency was significantly lower and oxygen consumption (v[Combining Dot Above]O2) was significantly higher when raising the saddle (GE = 19.9 ± 1.5%; V[Combining Dot Above]O2max = 43.8 ml·kg·min) than when lowering it (GE = 20.4 ± 1.3%; V[Combining Dot Above]O2 = 42.8 ml·kg·min). Additionally, a change of 0.8% in GE (20.6 ± 1.6% to 19.8 ± 1.6%, p < 0.05) was observed when comparing the positions where the best and worst GE was obtained. A significant effect of the small changes in saddle height on lower limb kinematics was also observed (p < 0.05). The differences between lower and higher saddle positions, in hip, knee, and ankle joints were an increase of extension (~4, 7, and 8°, respectively), a decrease of flexion (~3, 4, and 4°, respectively) and, consequently, an increase of the range of movement (~1, 3, and 4°, respectively). The results of the present study indicate that small changes in saddle height affected GE and lower limb kinematics The observed changes in lower limb kinematics could justify, in part, the GE changes. Further research should evaluate long-term effects of these small modifications in the seat height on GE and lower limb kinematics.

Diminished sub-maximal quadriceps force control in anterior cruciate ligament reconstructed patients is related to quadriceps and hamstring muscle dyskinesia

The aim of this study was to determine the effects of anterior cruciate ligament reconstruction (ACLR) on sub-maximal quadriceps force control with respect to quadriceps and hamstring muscle activity. Thirty ACLR individuals together with 30 healthy individuals participated. With real-time visual feedback of muscle force output and electromyographic electrodes attached to the quadriceps and hamstring muscles, subjects performed an isometric knee extension task where they increased and decreased their muscle force output at 0.128Hz within a range of 5-30% maximum voluntary capacity. The ACLR group completed the task with more error and increased medial hamstring and vastus medialis activation (p<0.05). Moderate negative correlations (p<0.05) were observed between quadriceps force control and medial (Spearman's rho=-0.448, p=0.022) and lateral (Spearman's rho=-0.401, p=0.034) hamstring activation in the ACLR group. Diminished quadriceps sub-maximal force control in ACLR subjects was reflective of medial quadriceps and hamstring dyskinesia (i.e., altered muscle activity patterns and coordination deficits). Within the ACLR group however, augmented hamstring co-activation was associated with better quadriceps force control. Future studies should explore the convergent validity of quadriceps force control in ACLR patients.

Adaptations in muscle activity to induced, short-term hindlimb lameness in trotting dogs

Muscle tissue has a great intrinsic adaptability to changing functional demands. Triggering more gradual responses such as tissue growth, the immediate responses to altered loading conditions involve changes in the activity. Because the reduction in a limb's function is associated with marked deviations in the gait pattern, understanding the muscular responses in laming animals will provide further insight into their compensatory mechanisms as well as help to improve treatment options to prevent musculoskeletal sequelae in chronic patients. Therefore, this study evaluated the changes in muscle activity in adaptation to a moderate, short-term, weight-bearing hindlimb lameness in two leg and one back muscle using surface electromyography (SEMG). In eight sound adult dogs that trotted on an instrumented treadmill, bilateral, bipolar recordings of the m. triceps brachii, the m. vastus lateralis and the m. longissimus dorsi were obtained before and after lameness was induced. Consistent with the unchanged vertical forces as well as temporal parameters, neither the timing nor the level of activity changed significantly in the m. triceps brachii. In the ipsilateral m. vastus lateralis, peak activity and integrated SEMG area were decreased, while they were significantly increased in the contralateral hindlimb. In both sides, the duration of the muscle activity was significantly longer due to a delayed offset. These observations are in accordance with previously described kinetic and kinematic changes as well as changes in muscle mass. Adaptations in the activity of the m. longissimus dorsi concerned primarily the unilateral activity and are discussed regarding known alterations in trunk and limb motions.