Effects of Fatigue and Recovery on Knee Mechanics during Side-Step Cutting

The effects of subsequent soccer-specific tasks on sidestep cutting kinematics and kinetics

OBJECTIVES

Sidestep cutting (SSC), a common method in soccer, frequently causes anterior cruciate ligament (ACL) injury. This study examined the effects of a soccer-specific movement task performed after a SSC on the kinematics and kinetics of the SSC.

DESIGN

Cross-sectional study.

SETTING

The participants performed SSC with a 90° change of direction in the following three conditions: running straight after SSC (Normal condition), kicking the ball after SSC (Kick condition), and jumping and heading after SSC (Heading condition).

PARTICIPANTS

Twenty healthy adult males with experience in soccer participated in this study.

MAIN OUTCOME MEASURES

Three-dimensional knee angles, moments, and ground reaction force (GRF) characteristics during the SSC were compared across conditions.

RESULTS

The knee valgus angle at foot contact and peak knee valgus moment of the supporting leg during SSC were significantly greater in the Normal condition compared to the Heading condition. Significant differences in GRF characteristics were mainly observed in braking impulse, propulsion impulse, and peak posterior GRF between conditions.

CONCLUSIONS

The SSC movement strategy should be a form that supports the efficient accomplishment of the subsequent task. Moreover, the Normal condition resulted in a posture more prone to non-contact ACL injury than the Heading condition.

Effects of Fatigue on Ankle Flexor Activity and Ground Reaction Forces in Elite Table Tennis Players

Fatigue specifically affects the force production capacity of the working muscle, leading to a decline in athletes' performance. This study investigated the impact of fatigue on ankle flexor muscle activity and ground reaction forces (GRFs) in elite table tennis players, with a focus on the implications for performance and injury risk. Twelve elite male table tennis athletes participated in this study, undergoing a fatigue protocol that simulated intense gameplay conditions. Muscle activity of the soleus (SOL) and gastrocnemius lateralis (GL) muscles, heel height, and GRFs were measured using a combination of wireless electromyography (EMG), motion capture, and force plate systems. Results showed a significant decrease in muscle activity in both legs post-fatigue, with a more pronounced decline in the right leg. This decrease in muscle activity negatively affected ankle joint flexibility, limiting heel lift-off. Interestingly, the maximal anteroposterior GRF generated by the left leg increased in the post-fatigue phase, suggesting the use of compensatory strategies to maintain balance and performance. These findings underscore the importance of managing fatigue, addressing muscle imbalances, and improving ankle flexibility and strength to optimize performance and reduce the risk of injuries.

Effects of Fatigue and Unanticipated Factors on Knee Joint Biomechanics in Female Basketball Players during Cutting

(1) This study examined the impact of fatigue and unanticipated factors on knee biomechanics during sidestep cutting and lateral shuffling in female basketball players, assessing the potential for non-contact anterior cruciate ligament (ACL) injuries. (2) Twenty-four female basketball players underwent fatigue induction and unanticipated change of direction tests, and kinematic and kinetic parameters were collected before and after fatigue with a Vicon motion capture system and Kistler ground reaction force (GRF) sensor. (3) Analysis using two-way repeated-measures ANOVA showed no significant interaction between fatigue and unanticipated factors on joint kinematics and kinetics. Unanticipated conditions significantly increased the knee joint flexion and extension angle (p < 0.01), decreased the knee flexion moment under anticipated conditions, and increased the knee valgus moment after fatigue (p ≤ 0.05). One-dimensional statistical parametric mapping (SPM1d) results indicated significant differences in GRF during sidestep cutting and knee inversion and rotation moments during lateral shuffling post-fatigue. (4) Unanticipated factors had a greater impact on knee load patterns, raising ACL injury risk. Fatigue and unanticipated factors were independent risk factors and should be considered separately in training programs to prevent lower limb injuries.

Time course of biomechanics during jump landing before and after two different fatigue tasks

Objective

Muscle fatigue contributes to anterior cruciate ligament (ACL) injuries, with increased knee and hip abduction observed during fatigue. However, there have been no reports revealing the differences between fatigue tasks or the duration of these changes. In this study, we conducted single-leg drop landings before and after hip and knee fatigue tasks to elucidate the changes in lower limb biomechanics over time.

Methods

Twenty-two male participants performed single-leg drop landings before, immediately after, and 5, 10, and 15 min after fatigue tasks involving isokinetic hip abduction/adduction (hip fatigue task [HFT]) and knee extension/flexion (knee fatigue task [KFT]). Hip and knee kinematic and kinetic data were collected using a three-dimensional motion analysis device and two force plates. A two-way ANOVA was performed with both the fatigue task (HFT and KFT) and time point (Time 1 to Time 4) as factors, and the main effects and interactions were calculated.

Results

The knee adduction angle after the HFT was significantly greater than that after KFT immediately following the fatigue task. The knee flexion moment was significantly lower in the KFT, whereas the knee adduction and internal rotation moments were significantly higher in the HFT immediately after the fatigue task.

Conclusion

This study revealed distinct kinematic and kinetic changes specific to each fatigue task, particularly in the frontal plane for hip joint tasks and the sagittal plane for knee joint tasks. These findings could assist in the development of ACL injury prevention programs tailored to the functional improvement and exercise capacity of each joint.

The effects of alteration in muscle activation on the iliotibial band during an exhaustive run

PURPOSE

Long exhausted running causes pain at the lateral femoral epicondyle for some runners. The pain has been revealed to be related to the behavior of the iliotibial band (ITB) during running. The purpose of this study is to examine the effects of in-series musculature on the behavior of the ITB in healthy participants during an exhaustive run.

METHODS

Twenty-five healthy participants (15 males, 10 females) were recruited in the current study. All participants performed a 30-minute exhaustive run at a self-selected speed with laboratory-provided footwear. Muscle activities of ITB-related muscles including tensor fascia latae (TFL), gluteus maximus (Gmax), gluteus medius (Gmed), biceps femoris (BF), and vastus lateralis (VL) were recorded using surface electromyography (EMG).

RESULTS

Maximum amplitudes at the initial stage (the first minute), the mid stage (the 15-minute), and the end stage (the 30-minute) were compared during the exhaustive running. Significant decreases (p < 0.05) were observed in the maximum amplitudes of the TFL, Gmax, Gmed, and BF at the mid (decreased by ~ 15%) and end (decreased by ~ 30%) stages compared to the initial stage. The onset and the offset remained unaltered during the running (p ≥ 0.05).

CONCLUSION

The behavior of the healthy ITB might be altered due to the activities of the in-series musculature. Excessive compression forces might be applied to the lateral femoral epicondyle from the ITB to provide stability for the knee joint during an exhaustive run. The findings could provide a basic understanding of the behavior of healthy ITB.

Effects of fatigue on balance and ankle proprioception during drop landing among individuals with and without chronic ankle instability

This study aimed to explore the effects of fatigue on the balance and ankle proprioception during drop landing of individuals with chronic ankle instability (CAI). A total of 35 participants with unilateral CAI and 35 healthy participants participated in this study. A static balance test, dynamic balance test, and ankle proprioception test were conducted before and after fatigue. Fatigue was induced with turn back runs and vertical jumps protocol. Sway distance of the center of pressure (COP), root mean square of the COP (RMS), total excursions (TOTEX), mean velocity (MVELO), 95% confidence ellipse area of the COP movements (95% AREA), Normalise Reach Distance in the anterior (ANT), posteromedial (PM), and posterolateral (PL) directions, and the area under the curve (AUC) were calculated and analyzed. There were significant group by fatigue interactions for static balance variables, normalise reach distance in the PM and PL directions, and AUC. Fatigue reduced balance and ankle proprioception in individuals with CAI. After fatigue, static and dynamic balance and ankle proprioception during drop landing were significantly worse in the CAI group than in the control group. Fatigue had a significant negative effect on balance and ankle proprioception in CAI patients. Therefore, fatigue may be an important factor causing repeated ankle sprain in CAI patients.

A facile inverse dynamics method to study the impacts of fatigue on the lower limb biomechanics

Fatigue can significantly affect the biomechanics of the anterior cruciate ligament (ACL) during single-legged jumping, and these changes are closely related to ACL injuries. Unfortunately, there is no convenient way to accurately and quickly track these changes. This present study aimed to develop such a method based on video capture and inverse dynamics simulation.Are our method's results accurate and reliable? Fifteen participants performed sing-legged jumping before and after the fatigue protocol, and their actions were videotaped. The videos were processed and converted to marked motion data, used to drive the mannequin model in AnyBody Modelling System (AMS) for the inverse dynamics simulations. The ACL segment was also constructed based on one participant's MRI data and added the mannequin model.Our results were similar to the findings from previous studies. Neuromuscular fatigue decreased the peak flexion angles and increased the low-the-limb muscle strength and activation. These alterations might contribute to ACL tears and ruptures. In addition, the simulation showed that the ACL force significantly (p < 0.05) increased as a result of fatigue during single-legged jumping. Our study provides a facile and reliable method to study the effects of neuromuscular fatigue on lower-the-limb biomechanics. Such a method can be applied to investigate other risk factors on ACL injuries and assist in developing workable plans for athlete training in the future.

Risk factors of young males with physically demanding occupations having accumulated damage of anterior cruciate ligament

Objective

To present the clinical characteristics of accumulated anterior cruciate ligament (ACL) damage among young male patients undergoing routine exercise, and to evaluate the related risk factors.

Methods

A retrospective study involving ACL‐accumulated damage from June 2015 to December 2019 was conducted. Baseline characteristics, such as age, body mass index (BMI), training parameters, and clinical signs, were recorded. The results of the radiologic examinations and related standardized tests were obtained to evaluate the research outcomes. These results were compared using Student's t‐test or Chi‐square test, and the impact of risk factors on the patient's injury were analyzed.

Results

A total of 86 men with accumulated ACL damage were included in this study. Exercise pain (86 [100%]), synovitis (80 [93.0%]), and intra‐articular effusion (79 [91.9%]) were the most common clinical symptoms. Loosening of ligaments, decreased tension, mild hyperplasia, and intercondylar fossa effusion were observed using radiography, magnetic resonance imaging, and arthroscopy. Age, BMI, training intensity, length of training, and knee hyperextension were identified as risk factors for accumulated ACL damage.

Conclusion

This study suggests that accumulated ACL damage has differentiated clinical symptoms, imaging features, and risk factors compared to common ACL injuries.

Fatigue and recovery have different effects on knee biomechanics of drop vertical jump between female collegiate and recreational athletes

Background

Although fatigue is known as one of the risk factors for noncontact anterior cruciate ligament injury, the effects of fatigue and recovery can be different based on the level of competition. However, it is unknown whether female recreational athletes are susceptible to fatigue or not, compared to female collegiate athletes with greater physical activity. The purpose of the present study was to examine and clarify the effects of fatigue and recovery on knee biomechanics of the drop vertical jump (DVJ) in female recreational athletes compared to female collegiate athletes.

Methods

Fifteen female collegiate athletes and ten female recreational athletes were enrolled in the current study. All subjects were basketball players and Tegner activity scales were level 9 and 7, respectively. They performed DVJ before and after the fatigue protocol. Three-dimensional knee kinematics and kinetics were collected during landing phase of DVJ. The data after the fatigue protocol (first, second, and third DVJs) were compared with those before the protocol using one-way repeated measures of analysis of variance in each group.

Results

Fatigue caused significant increase of knee abduction angle at initial contact (IC) and peak abduction moments within 40 ms from IC in female recreational athletes, whereas no increases of these parameters were observed in female collegiate athletes. Moreover, recovery from fatigue seemed to be more slowly in female recreational athletes than in female collegiate athletes as smaller knee flexion moment was observed even in post-fatigue third DVJ only for female recreational athletes.

Conclusions

Effects of fatigue on DVJ were significantly greater and continued for a longer duration in female recreational athletes compared to female collegiate athletes.

The effect of performance demands on lower extremity biomechanics during landing and cutting tasks

BACKGROUND

Anterior cruciate ligament (ACL) injuries commonly occur during the early phase of landing and cutting tasks that involve sudden decelerations. The purpose of this study was to investigate the effects of jump height and jump speed on lower extremity biomechanics during a stop-jump task and the effect of cutting speed on lower extremity biomechanics during a side-cutting task.

METHODS

Thirty-six recreational athletes performed a stop-jump task under 3 conditions: jumping fast, jumping for maximum height, and jumping for 60% of maximum height. Participants also performed a side-cutting task under 2 conditions: cutting at maximum speed and cutting at 60% of maximum speed. Three-dimensional kinematic and kinetic data were collected.

RESULTS

The jumping fast condition resulted in increased peak posterior ground reaction force (PPGRF), knee extension moment at PPGRF, and knee joint stiffness and decreased knee flexion angle compared with the jumping for maximum height condition. The jumping for 60% of maximum height condition resulted in decreased knee flexion angle compared with the jumping for maximum height condition. Participants demonstrated greater PPGRF, knee extension moment at PPGRF, knee valgus angle and varus moment at PPGRF, knee joint stiffness, and knee flexion angle during the cutting at maximum speed condition compared with the cutting at 60% maximum speed condition.

CONCLUSION

Performing jump landing at an increased jump speed resulted in lower extremity movement patterns that have been previously associated with an increase in ACL loading. Cutting speed also affected lower extremity biomechanics. Jump speed and cutting speed need to be considered when designing ACL injury risk screening and injury prevention programs.

Single-leg vertical jump test as a functional test after anterior cruciate ligament reconstruction

BACKGROUND

The aim of this study was to identify the correlations between the single-leg vertical jump (SLVJ) test and subjective and objective tests which were used widely for determining return-to-sports (RTS) after anterior cruciate ligament reconstruction (ACLR).

METHODS

Seventy-five patients (29.5 ± 9.2 years) who underwent ACLR between May 2012 and Jan 2014 were included. Subjective knee scoring systems including subjective International Knee Documentation Committee (IKDC) score, Lysholm score, Tegner activity scale, and ACL-Return to Sports after Injury (ACL-RSI) scale were assessed. Objective tests were also performed.

RESULTS

The limb symmetry index (LSI) for SLVJ test and single-leg hop for distance (SLHD) test was 89.4 ± 14.9% and 90.7 ± 11.7%. LSI for SLVJ test was correlated to subjective IKDC scores (r = 0.26, P = 0.024), Tegner activity scale (r = 0.64, P < 0.001), ACL-RSI scale (r = 0.61, P < 0.001), LSI for SLHD (r = 0.45, P < 0.001), Co-contraction (r = -0.57, P < 0.001), Shuttle run (r = -0.52, P < 0.001), and Carioca (r = -0.54, P < 0.001) tests. In isokinetic strength tests, extensor peak torque (r = 0.30, P = 0.009) and extensor strength deficit (r = -0.41, P < 0.001) were correlated with LSI for SLVJ test.

CONCLUSION

There were considerable correlations between SLVJ test and subjective IKDC scores, Tegner activity scale, ACL-RSI scale, isokinetic extensor muscle strength, and all other functional tests. SLVJ test could be used conveniently to determine RTS after ACLR in outpatient clinics.

LEVEL OF EVIDENCE

Level IV, case series.

Effects of Two Fatigue Protocols on Impact Forces and Lower Extremity Kinematics during Drop Landings: Implications for Noncontact Anterior Cruciate Ligament Injury

The purpose of the study was to determine the effects of fatigue on the impact forces and sagittal plane kinematics of the lower extremities in a drop landing task. 15 male collegiate athletes were recruited. Five successful trials of a drop landing task were obtained during prefatigue and postfatigue in two fatigue protocols (constant speed running fatigue protocol [R-FP] and shuttle running + vertical jumping fatigue protocol [SV-FP]). Duration time, maximal heart rate, and RPE of each protocol were measured separately. Kinematic measures of the hip, knee, and ankle joints at different times coupled with peak impact force and loading rate were acquired. Our results showed a more flexed landing posture due to an increase in hip and knee flexion angles in the postfatigue condition. However, no differences in peak impact force and loading rate were found between pre- and postfatigue conditions. The changes were similar between protocols, but the SV-FP showed a significantly shorter exercise duration time than the R-FP. Fatigued athletes in this study demonstrated altered motor control strategies during a drop landing task, which may be an intentional or unintentional protective strategy for preventing themselves from potential ACL injury.

Influence of a 12.8-km military load carriage activity on lower limb gait mechanics and muscle activity

The high stress fracture occurrence in military populations has been associated with frequent load carriage activities. This study aimed to assess the influence of load carriage and of completing a load carriage training activity on gait characteristics. Thirty-two Royal Marine recruits completed a 12.8-km load carriage activity as part of their military training. Data were collected during walking in military boots, pre and post-activity, with and without the additional load (35.5 kg). Ground contact time, lower limb sagittal plane kinematics and kinetics, and electromyographic variables were obtained for each condition. When carrying load, there was increased ground contact time, increased joint flexion and joint moments, and increased plantar flexor and knee extensor muscle activity. Post-activity, there were no changes to kinematic variables, knee extensor moments were reduced, and there was evidence of plantar flexor muscle fatigue. The observed gait changes may be associated with stress fracture development. Practitioner Summary: This study identified gait changes due to load carriage and after a military load carriage training activity. Such activities are associated with lower limb stress fractures. A pre-post study design was used. Gait mechanics changed to a greater extent when carrying load, than after completion of the activity when assessed without load.

Functional performance 2-9 years after ACL reconstruction: cross-sectional comparison between athletes with bone-patellar tendon-bone, semitendinosus/gracilis and healthy controls

PURPOSE

The purpose of this cross-sectional study was to provide descriptive data on functional performance in men and women with ACLR, to compare bone-patellar tendon-bone (BPTB) with semitendinosus/gracilis (STG) within the same sex and to compare the ACLR subjects with healthy controls.

METHODS

Eligible participants comprised 100 men (43 % BPTB) and 84 women (41 % BPTB) after ACLR, of whom 30 men (STG n = 19; BPTB n = 11) and 18 women (STG n = 12; BPTB n = 6) were untraceable/not willing and 15 men (STG n = 9; BPTB n = 6) and 18 women (STG n = 12; BPTB n = 3) were not able to take part in the measurements because of injury. Besides men BPTB (n = 24), men STG (n = 27), women BPTB (n = 23) and women STG (n = 23), healthy men (n = 22) and women (n = 22) participated. Measurements consisted of questionnaires, isokinetic peak torque and endurance tests, a hop test battery and drop jump including video analysis.

RESULTS

Only the occurrence of dynamic knee valgus differed between ACLR and healthy subjects.

CONCLUSION

Two to nine years after ACLR, 16 % of athletes could not participate because of a lower extremity injury. In the remaining group, this study showed similar results for males and females with BPTB compared with STG. Also, similar results are found for quantity of movement comparing operated and healthy subjects. For quality of movement, only the occurrence of dynamic knee valgus in landing from a jump is higher in operated subjects compared with healthy controls. This supports the relevance of a focus on quality of movement as part of ACLR rehabilitation programmes and return to sports criteria.

LEVEL OF EVIDENCE

III.

The Effect of Exertion and Sex on Vertical Ground Reaction Force Variables and Landing Mechanics

The purpose of this investigation was to determine how exertion and sex affected a variety of vertical ground reaction force (VGRF) parameters during a jump-landing task, including peak VGRF, peak VGRF asymmetry, loading rate, and loading rate asymmetry. Additionally, we wanted to determine whether landing mechanics changed after exertion as measured by the Landing Error Scoring System (LESS). Forty recreationally active participants (20 men and 20 women) completed jump landings from a 30-cm-high box onto force plates before and after repeated bouts of an exercise circuit until a specific rating of perceived exertion was achieved. Three-way (sex × time × limb) analyses of variance were used to analyze variables pre-exertion to postexertion. No significant 3-way interactions were observed for peak VGRF (p = 0.31) or loading rate (p = 0.14). Time by sex interactions were observed for peak VGRF (p = 0.02) and loading rate (p = 0.008). Post hoc analysis revealed that men increased landing force and loading rate after exertion while women did not. Landing mechanics, as assessed by total LESS score, were worse after exertion (p < 0.001) with increased frequency of errors for knee flexion <30° at initial contact, lateral trunk flexion, and not flexing the hip during landing. Women may be more resistant to exertion compared with men and use different joint controls' strategies to cope with VGRF after exertion. However, VGRF asymmetry is not affected by sex and exertion. Limiting peak VGRF and addressing landing postures, especially after exertion, should be components of injury prevention strategies.

Mapping current research trends on anterior cruciate ligament injury risk against the existing evidence: In vivo biomechanical risk factors

BACKGROUND

Whilst many studies measure large numbers of biomechanical parameters and associate these to anterior cruciate ligament injury risk, they cannot be considered as anterior cruciate ligament injury risk factors without evidence from prospective studies. A review was conducted to systematically assess the in vivo biomechanical literature to identify biomechanical risk factors for non-contact anterior cruciate ligament injury during dynamic sports tasks; and to critically evaluate the research trends from retrospective and associative studies investigating non-contact anterior cruciate ligament injury risk.

METHODS

An electronic literature search was undertaken on studies examining in vivo biomechanical risk factors associated with non-contact anterior cruciate ligament injury. The relevant studies were assessed by classification; level 1 - a prospective cohort study, level 2 - a retrospective study or level 3 - an associative study.

FINDINGS

An initial search revealed 812 studies but this was reduced to 1 level 1 evidence study, 20 level 2 evidence studies and 175 level 3 evidence studies that met all inclusion criteria. Level 1 evidence showed that the knee abduction angle, knee abduction moment and ground reaction force were biomechanical risk factors. Nine level 2 studies and eighty-three level 3 studies used these to assess risk factors in their study. Inconsistencies in results and methods were observed in level 2 and 3 studies.

INTERPRETATION

There is a lack of high quality, prospective level 1 evidence related to biomechanical risk factors for non-contact anterior cruciate ligament injury. More prospective cohort studies are required to determine risk factors and provide improved prognostic capability.

Sex Differences in Knee Flexion Angle During a Rapid Change of Direction While Running

BACKGROUND

Females experience greater overall rates of athletic anterior cruciate ligament (ACL) injury than males. The specific mechanisms of the predisposition remain unclear.

HYPOTHESIS

Modeling of knee kinematics has shown that the more extended the knee joint, the greater the strain on the ACL. The authors hypothesized that female athletes would have a lesser degree of knee flexion than male athletes at initial ground contact while performing change-of-direction cutting maneuvers.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty female and 20 male high school soccer athletes with at least 1 year of experience were recruited for the study. Athletes were excluded if they had a history of any major lower limb injury or current knee pain causing a reduction in training and/or competition. Reflective markers were attached at the greater trochanter of the femur, the lateral epicondyle of the knee, and the lateral malleolus of the ankle to enable motion capture. Each athlete performed 6 change-of-direction maneuvers in random order in front of 2 cameras. Multiple regression analysis was used to determine differences between the sexes from the motion data captured; P < .05 defined significance.

RESULTS

Statistically significant differences existed in knee flexion angles between male and female participants at the 90° and 135° cutting angles. At 90°, males and females showed initial contact knee flexion angles (mean ± SD) of 39.0° ± 6.8° and 29.3° ± 6.2°, respectively (P < .0001), and mean maximum flexion angles of 56.4° ± 6.9° and 49.7° ± 7.0°, respectively (P = .0036). At 135°, males and females showed mean initial contact knee flexion angles of 36.8° ± 7.9° and 29.7° ± 7.8°, respectively (P = .0053), and mean maximum flexion angles of 60.7° ± 8.1° and 51.6° ± 9.4°, respectively (P = .0017).

CONCLUSION

The research conducted is intended to foster an awareness of injury disposition in female athletes and guide future endeavors to develop, test, and implement a proactive approach in lowering female noncontact athletic ACL injury rates. This project adds to the literature as wider side-cut maneuvers (≥90°) were studied, as compared with previous studies using small side-cut angles (<90°), offering a model for alternative sports actions.

Efficacy of the functional movement screen: a review

The aim of this review was to evaluate and synthesize the scientific literature of the functional movement screen (FMS)-driven research for scientists and strength and conditioning specialists. An additional purpose was to optimize the methodological quality of prospective studies. Relevant research was identified through using a manual and electronically database search. Thirty-four articles met the inclusion criteria and were read, abstracted, and coded for this review. The publications were classified into different stages of Bishops Applied Research Model for the Sport Sciences (ARMSS). Thirteen descriptive studies explored the main tasks in test development like factor structure, objectivity, and reliability. They can be classified to the second stage of Bishops Model (ARMSS stage 2). Twelve studies covered ability of FMS to predict sporting performance and injury risk (ARMSS stages 3 and 4). Seven studies investigated the effectiveness of the FMS in designing programs (ARMSS stages 6 and 8). In addition, 2 assessed norming data. On the descriptive level, results suggest that the FMS is a reliable screen, if the rater is educated and has solid experience (>100 trials). Factor analysis describes the FMS as a unitary construct, which is an argument against the FMS total score. Studies clearly illustrate its limited ability to predict athletic performance. On the contrary, to predict injury risk in team sports, the FMS total score is supported by moderate scientific evidence. The majority of the FMS based intervention programs showed an improvement on general motor quality. However, a randomized trial does not confirm that results. Hence, to implement the findings on field, a critical strength and conditioning specialist is crucial.

Repetitive jumping and sprinting until exhaustion alters hamstring reflex responses and tibial translation in males and females

The incidence of anterior cruciate ligament injuries is considerably higher in females than in males and the underlying mechanisms are still under debate. Research indicates that the neuromuscular system of females and males might respond differently to the same fatigue protocol due to differences in muscle activation during movement tasks. This study analyzed sex differences in hamstring reflex responses and posterior-anterior tibial translation (TT) before and after fatiguing exercise. We measured the isolated movement of the tibia relative to the femur as a consequence of mechanically induced TT in standing subjects as well as muscle activity of the hamstrings before and after repetitive jumping and sprinting until exhaustion. Muscle fatigue delayed reflex onset latencies in females and males. A reduction in reflex responses associated with an increased TT was observed after fatiguing exercise for both sexes. Data indicate that the used fatigue protocol altered the latency and magnitude of reflex responses as well as TT in females and males. Based on the results of previous research and the outcome of this study, it might be that sex-specific effects of fatigue on reflex activity and mechanical stability of the knee depend on the kind of fatiguing exercise.

Quadriceps muscle function after exercise in men and women with a history of anterior cruciate ligament reconstruction

CONTEXT

Sex differences in lower extremity neuromuscular function have been reported after anterior cruciate ligament reconstruction (ACLR). Research evidence supports different levels of fatigability in men and women and between patients with ACLR and healthy controls. The influence of sex on the response to continuous exercise in patients with ACLR is not clear.

OBJECTIVE

To compare quadriceps neuromuscular function after exercise between men and women with ACLR.

DESIGN

Descriptive laboratory study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty-six active volunteers (13 men [50%]: age = 24.1 ± 4.4 years, height = 179.1 ± 9.8 cm, mass = 80.1 ± 9.4 kg, months since surgery = 43.5 ± 37.0; 13 women [50%]: age = 24.2 ± 5.6 years, height = 163.0 ± 5.9 cm, mass = 62.3 ± 8.3 kg, months since surgery = 45.8 ± 42.7) with a history of unilateral primary ACLR at least 6 months earlier.

INTERVENTION(S)

Thirty minutes of continuous exercise comprising 5 separate 6-minute cycles, including 5 minutes of uphill walking and 1 minute of body-weight squatting and step-ups.

MAIN OUTCOME MEASURE(S)

Normalized knee-extension maximal voluntary isometric contraction torque, quadriceps superimposed-burst torque, and quadriceps central activation ratio before and after exercise. We performed separate 2 (sex: men, women) × 2 (time: preexercise, postexercise) repeated-measures analyses of variance for the 3 variables. Separate, independent-samples t tests were calculated to compare preexercise with postexercise change in all dependent variables between sexes.

RESULTS

A significant group-by-time interaction was present for knee-extension torque (P = .04). The percentage reduction in knee-extension maximal voluntary isometric contraction torque (men = 1.94%, women = -10.32%; P = .02) and quadriceps central activation ratio (men = -1.45%, women = -8.69%; P = .03) experienced by men was less than that observed in women.

CONCLUSIONS

In the presence of quadriceps dysfunction, female participants experienced greater-magnitude reductions in quadriceps function after 30 minutes of exercise than male participants. This indicates a reduced ability to absorb knee-joint loads, which may have significant implications for reinjury and joint osteoarthritis in women after ACLR.

What is normal? Female lower limb kinematic profiles during athletic tasks used to examine anterior cruciate ligament injury risk: a systematic review

BACKGROUND

It has been proposed that the performance of athletic tasks where normal motion is exceeded has the potential to damage the anterior cruciate ligament (ACL). Determining the expected or 'normal' kinematic profile of athletic tasks commonly used to assess ACL injury risk can provide an evidence base for the identification of abnormal or anomalous task performances in a laboratory setting.

OBJECTIVE

The objective was to conduct a systematic review of studies examining lower limb kinematics of females during drop landing, drop vertical jump, and side-step cutting tasks, to determine 'normal' ranges for hip and knee joint kinematic variables.

DATA SOURCES

An electronic database search was conducted on the SPORTDiscus(TM), MEDLINE, AMED and CINAHL (January 1980-August 2013) databases using a combination of relevant keywords.

STUDY SELECTION

Studies identified as potentially relevant were independently examined by two reviewers for inclusion. Where consensus could not be reached, a third reviewer was consulted. Original research articles that examined three-dimensional hip and knee kinematics of female subjects during the athletic tasks of interest were included for review. Articles were excluded if subjects had a history of lower back or lower limb joint injury or isolated data from the female cohort could not be extracted.

STUDY APPRAISAL AND SYNTHESIS METHODS

Two reviewers independently assessed the quality of included studies. Data on subject characteristics, the athletic task performed, and kinematic data were extracted from included studies. Studies were categorised according to the athletic task being examined and each study allocated a weight within categories based on the number of subjects assessed. Extracted data were used to calculate the weighted means and standard deviations for hip and knee kinematics (initial contact and peak values). 'Normal' motion was classified as the weighted mean plus/minus one standard deviation.

RESULTS

Of 2,920 citations, a total of 159 articles were identified as potentially relevant, with 29 meeting all inclusion/exclusion criteria. Due to the limited number of studies available examining double-leg drop landings and single-leg drop vertical jumps, insufficient data was available to include these tasks in the review. Therefore, a total of 25 articles were included. From the included studies, 'normal' ranges were calculated for the kinematic variables of interest across the athletic tasks examined.

LIMITATIONS

Joint forces and other additional elements play a role in ACL injuries, therefore, focusing solely on lower limb kinematics in classifying injury risk may not encapsulate all relevant factors. Insufficient data resulted in no normal ranges being calculated for double-leg drop land and single-leg drop vertical jump tasks. No included study examined hip internal/external rotation during single-leg drop landings, therefore ranges for this kinematic variable could not be determined. Variation in data between studies resulted in wide normal ranges being observed across certain kinematic variables.

CONCLUSIONS

The ranges calculated in this review provide evidence-based values that can be used to identify abnormal or anomalous athletic task performances on a multi-planar scale. This may be useful in identifying neuromuscular factors or specific muscular recruitment strategies that contribute to ACL injury risk.

Changes of direction during high-intensity intermittent runs: neuromuscular and metabolic responses

BACKGROUND

The ability to sustain brief high-intensity intermittent efforts (HIE) is meant to be a major attribute for performance in team sports. Adding changes of direction to HIE is believed to increase the specificity of training drills with respect to game demands. The aim of this study was to investigate the influence of 90°-changes of direction (COD) during HIE on metabolic and neuromuscular responses.

METHODS

Eleven male, team sport players (30.5 ± 3.6 y) performed randomly HIE without (straight-line, 2×[10× 22 m]) or with (2×[10× ~16.5 m]) two 90°-COD. To account for the time lost while changing direction, the distance for COD runs during HIE was individually adjusted using the ratio between straight-line and COD sprints. Players also performed 2 countermovement (CMJ) and 2 drop (DJ) jumps, during and post HIE. Pulmonary oxygen uptake (VO2), quadriceps and hamstring oxygenation, blood lactate concentration (Δ[La]b), electromyography amplitude (RMS) of eight lower limb muscles and rating of perceived exertion (RPE) were measured for each condition.

RESULTS

During HIE, CODs had no substantial effects on changes in VO2, oxygenation, CMJ and DJ performance and RPE (all differences in the changes rated as unclear). Conversely, compared with straight-line runs, COD-runs were associated with a possibly higher Δ[La]b (+9.7 ± 10.4%, with chances for greater/similar/lower values of 57/42/0%) and either a lower (i.e., -11.9 ± 14.6%, 2/13/85 for semitendinosus and -8.5 ± 9.3%, 1/21/78 for lateral gastrocnemius) or equivalent decrease in electromyography amplitude.

CONCLUSION

Adding two 90°-CODs on adjusted distance during two sets of HIE is likely to elicit equivalent decreases in CMJ and DJ height, and similar cardiorespiratory and perceptual responses, despite a lower average running speed. A fatigue-induced modification in lower limb control observed with CODs may have elicited a selective reduction of electromyography activity in hamstring muscles and may induce, in turn, a potential mechanical loss of knee stability. Therefore, changing direction during HIE, with adjusted COD running distances, might be an effective training practice 1) to manipulate some components of the acute physiological load of HIE, 2) to promote long-term COD-specific neuromuscular adaptations aimed at improving performance and knee joint stability.

Assessment of functional performance after anterior cruciate ligament reconstruction: a systematic review of measurement procedures

PURPOSE

The purpose of this systematic review was to identify the measurements that are used in clinical practice to assess the quantity and quality of functional performance in men and women more than 2 years after ACL reconstruction with bone patellar-tendon bone (BPTB) or semitendinosus/gracilis (STG) graft.

METHODS

A systematic literature search was performed in Medline (Pubmed), EMBASE (OVID), the Cochrane Library and PEDro to identify relevant articles from 1990 up to 2010. Articles were included if they described functional performance after BPTB or STG reconstruction and had a follow-up of more than 2 years. Two authors screened the selected articles for title, abstract and full-text in accordance with predefined inclusion and exclusion criteria. The methodological quality of all articles was assessed by checklists of the Cochrane Library by two authors. Only the articles with good methodological quality were considered for further analysis.

RESULTS

A total of 27 studies were included by full-text. According to their methodological quality six were rated as good. Different authors used different study designs for muscle testing which led to different outcomes that could not be compared. Besides strength, a single-leg hop for distance was used as a measurement for quantity of functional performance. No measurements for quality of functional performance were reported.

CONCLUSIONS

Measurement of functional performance more than 2 years after ACL reconstruction consists of concentric or isometric strength, the single-leg hop for distance or a combination. The Limb Symmetry Index is used as the main outcome parameter to compare the involved leg with the uninvolved. In all studies the results of men and woman are combined. Based on our findings and previous studies that discussed additional important parameters a more extensive test battery to assess functional performance is suggested.

Effect of fatigue on hamstring reflex responses and posterior-anterior tibial translation in men and women

Anterior cruciate ligament (ACL) rupture ranks among the most common injuries in sports. The incidence of ACL injuries is considerably higher in females than in males and the underlying mechanisms are still under debate. Furthermore, it has been suggested that muscle fatigue can be a risk factor for ACL injuries. We investigated gender differences in hamstring reflex responses and posterior-anterior tibial translation (TT) before and after fatiguing exercise. We assessed the isolated movement of the tibia relative to the femur in the sagittal plane as a consequence of mechanically induced TT in standing subjects. The muscle activity of the hamstrings was evaluated. Furthermore, isometric maximum voluntary torque (iMVT) and rate of torque development (RTD) of the hamstrings (H) and quadriceps (Q) were measured and the MVT H/Q as well as the RTD H/Q ratios were calculated. After fatigue, reflex onset latencies were enhanced in women. A reduction of reflex responses associated with an increased TT was observed in females. Men showed no differences in these parameters. Correlation analysis revealed no significant associations between parameters for TT and MVT H/Q as well as RTD H/Q. The results of the present study revealed that the fatigue protocol used in this study altered the latency and magnitude of reflex responses of the hamstrings as well as TT in women. These changes were not found in men. Based on our results, it is conceivable that the fatigue-induced decrease in neuromuscular function with a corresponding increase in TT probably contributes to the higher incidence of ACL injuries in women.

Effect of fatigue on tibial rotation after single- and double-bundle anterior cruciate ligament reconstruction: a 3-dimensional kinematic and kinetic matched-group analysis

BACKGROUND

Fatigue is an extrinsic factor adversely affecting joint proprioception and neuromuscular response, thereby increasing anterior cruciate ligament (ACL) strain and injury risk. The effectiveness of the single- and double-bundle techniques for ACL reconstruction to control residual rotational knee laxity under fatigue has not been examined.

HYPOTHESIS

Fatigue results in a significant increase in tibial rotation angles and moments in both ACL-intact and single- and double-bundle ACL-reconstructed knees. The 2 groups with ACL-reconstructed knees will show no significant differences in tibial rotation angles and moments either pre- or postfatigue.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty-four male patients who underwent successful single-bundle (n = 12) or double-bundle (n = 12) ACL reconstructions and 10 matched healthy controls were subjected to a standard lower limb muscle fatigue protocol using an isokinetic dynamometer. Three-dimensional motion analysis was used to measure tibial rotation and rotational knee moments in the pre- and postfatigue states, during a swinging maneuver on the weightbearing leg from a standing position with the knee in extension.

RESULTS

Tibial rotation of the single-bundle group significantly increased postfatigue (prefatigue 22° ± 10° vs 29° ± 15° postfatigue, P = .015). In contrast, the double-bundle group showed similar tibial rotation values pre- and postfatigue (16° ± 6° vs 18° ± 4°, P = .22). The double-bundle group showed a trend toward decreased tibial rotation values pre- and post-fatigue compared with controls (22 ± 4 and 23 ± 4) (P = .065 and .08, respectively). In the prefatigue state, rotational moments (N·mm/Kg) of the single-bundle (339 ± 148) and double-bundle (317 ± 97) groups were significantly lower than that of controls (465 ± 134) (P = .05 and .03, respectively). In the postfatigue state, an increase was observed in rotational moments of the single-bundle (388 ± 131) and double-bundle (408 ± 187) groups compared with prefatigue values, whereas a decrease was noted in the control group (411 ± 117).

CONCLUSION

Single-bundle ACL-reconstructed knees demonstrate a reduced ability to resist rotational loads under fatigue. Double-bundle reconstructed knees had significantly better control of tibial rotation when fatigued. However, they demonstrate an excessive, yet not significant, reduction in tibial rotation compared with the intact knee, suggesting a possible overcorrection in rotational laxity.