The cumulative and residual fatigue response associated with soccer-specific activity performed on different playing surfaces

ABSTRACT

This study aimed to assess the effect of playing surface (Natural [NT] and Artificial [AT] Turf) on the fatigue response to a soccer-specific exercise protocol (SSEP). Eighteen male soccer players completed the SSEP on NT and AT with pre-, post-, and 48 h post-assessments of eccentric knee flexor (eccKF) and concentric knee extensor peak torque (PT), peak countermovement (CMJ) and squat jump (SJ) height, and Nordic hamstring break angle. No significant main effects for surface or any surface and time interactions were observed for any of the outcome measures, except for eccKF PT recorded at 3.14 rad·s^-1, which was significantly lower 48 h post-trial in the AT condition (AT = 146.3 ± 20.4 Nm; NT = 158.8 ± 24.7 Nm). Main effects for time were observed between pre- and post-trial measures for eccKF PT at all angular velocities, Nordic break angle, CMJ and SJ height. Nordic break angle, and both CMJ and SJ height were significantly impaired 48 h post-trial when compared to pre-trial. The findings of the current study suggest surface dependent changes in eccKF PT which may have implications for recovery and subsequent performance after competition on AT.     

Estimates of voluntary activation in individuals with anterior cruciate ligament reconstruction: Effects of type of stimulator,number of stimuli,and quantification technique

Background:Accurate quantification of voluntary activation is important for understanding the extent of quadriceps dysfunction in individuals with anterior cruciate ligament reconstruction(ACLR).Voluntary activation has been quantified using both percent activation derived from the interpolated twitch technique and central activation ratio(CAR)derived from the burst superimposition technique,as well as by using different types of electrical stimulators and pulse train conditions.However,it is unclear how these parameters affect voluntary activation estimates in individuals with ACLR.This study was performed to fill this important knowledge gap in the anterior cruciate ligament literature.Methods:Quadriceps strength and voluntary activation were examined in 18 ACLR participants(12 quadriceps/patellartendon graft,6 hamstring tendon graft;time since ACLR:1.06±0.82 years,mean±SD)at 90°of knee flexion using 2 stimulators(Digitimer and Grass)and pulse train conditions(3-pulse and 10-pulse).Voluntary activation was quantified by calculating both CAR and percent activation.Results:Results indicated that voluntary activation was significantly overestimated by CAR when compared with percent activation(p<0.001).Voluntary activation estimates were not affected by pulse train conditions when using percent activation;however,3-pulse stimuli resulted in greater overestimation than 10-pulse stimuli when using CAR(p=0.003).Voluntary activation did not differ between stimulators(p>0.05);however,the Digitimer evoked greater torque at rest than the Grass(p<0.001).Conclusion:These results indicate that percent activation derived from the interpolated twitch technique provides superior estimates of voluntary activation than CAR derived from burst superimposition and is less affected by pulse train conditions or stimulators in individuals with ACLR.     

A biomechanical investigation of right-forward lunging step among badminton players

This study presents the kinematics and plantar pressure characteristics of eight elite national-level badminton athletes and eight recreational college-level badminton players while performing a right-forward lunge movement in a laboratory-simulated badminton court. The hypothesis was that recreational players would be significantly different from elite players in kinematics and plantar pressure measures. Vicon^® motion capture and Novel^® insole plantar pressure measurement were simultaneously taken to record the lower extremity kinematics and foot loading during stance. Recreational players showed significantly higher peak pressure in the lateral forefoot (P = 0.002) and force time integral in the lateral forefoot (P = 0.013) and other toes (P = 0.005). Elite athletes showed higher peak pressure in the medial forefoot (P = 0.003), hallux (P = 0.037) and force time integral in the medial forefoot (P = 0.009). The difference in landing techniques for the lunge step between elite athletes and recreational players was observed with peak ankle eversion (?38.2°±2.4° for athletes and ?11.1°±3.9° for players, P = 0.015); smaller knee range of motion in the coronal and transverse planes, with differences in peak knee adduction (28.9°±6.8° for athletes and 15.7°±6.2° for players, P = 0.031); peak knee internal rotation (20.3°±1.3° for athletes and 11.8°±3.2° for players, P = 0.029) and peak hip flexion (77.3°±4.1° for athletes and 91.3°±9.3° for players, P = 0.037).     

Sex-related differences in joint-angle-specific hamstring-to-quadriceps function following fatigue

Abstract

The purpose of this study was to examine the effect of fatiguing exercise on sex-related differences in the function of hamstring and quadriceps muscles at several angular velocities and joint angles. Physically active participants (50 male: 28.7?±?4.5y, 1.82?±?0.07 m, 82.3?±?6.87?kg; 50 female: 27.0?±?5.8y, 1.61?±?0.08 m, 68.75?±?9.24?kg) carried out an isokinetic assessment to determine concentric and eccentric torques during knee extension and flexion actions at three different angular velocities (60/180/300°/s). The H/Q_FUNCT was calculated using peak torque (PT) values at 3 different joint-angle-specific (15°, 30° and 45° of knee flexion). A repeated measures analysis of variance (ANOVA) was used to compare within group results. Between group comparisons of sex-related differences were assessed by independent T-tests. Fatiguing exercise in males resulted in a decrease in H/Q_FUNCT ratios for each angle of knee flexion at both 60°/s and 300°/s angular velocities (p?<?0.05). In females, significant decreases in H/Q_FUNCT ratios were observed following fatiguing exercise for each angle of knee flexion and angular velocity (p?<?0.01). Significant differences in H/Q_FUNCT ratios following fatiguing exercise were evident between males and females at each joint angle and angular velocity (p?<?0.01). These findings indicate sex related differences in H/Q_FUNCT ratios following fatiguing exercise. Females have greater reductions in torque and H/Q_FUNCT ratios following fatigue than their male counterparts. This potentially exposes females to higher risks of injury, particularly when fatigued. Practitioners should attend to the imbalance in fatigue resistance of hamstring and quadriceps function, particularly in female athletes.     

A systematic review of running-related musculoskeletal injuries in runners

ObjectiveRunning-related musculoskeletal injuries (RRMIs), especially stemming from overuse, frequently occur in runners. This study aimed to systematically review the literature and determine the incidence and prevalence proportion of RRMIs by anatomic location and specific pathology.MethodsAn electronic database search with no date beginning restrictions was performed in SPORTDiscus, PubMed, and MEDLINE up to June 2020. Prospective studies were used to find the anatomic location and the incidence proportion of each RRMI, whereas retrospective or cross-sectional studies were used to find the prevalence proportion of each RRMI. A separate analysis for ultramarathon runners was performed.ResultsThe overall injury incidence and prevalence were 40.2% ± 18.8% and 44.6% ± 18.4% (mean ± SD), respectively. The knee, ankle, and lower leg accounted for the highest proportion of injury incidence, whereas the knee, lower leg, and foot/toes had the highest proportion of injury prevalence. Achilles tendinopathy (10.3%), medial tibial stress syndrome (9.4%), patellofemoral pain syndrome (6.3%), plantar fasciitis (6.1%), and ankle sprains (5.8%) accounted for the highest proportion of injury incidence, whereas patellofemoral pain syndrome (16.7%), medial tibial stress syndrome (9.1%), plantar fasciitis (7.9%), iliotibial band syndrome (7.9%), and Achilles tendinopathy (6.6%) had the highest proportion of injury prevalence. The ankle (34.5%), knee (28.1%), and lower leg (12.9%) were the 3 most frequently injured sites among ultramarathoners.ConclusionThe injury incidence proportions by anatomic location between ultramarathoners and non-ultramarathoners were not significantly different (p = 0.798). The pathologies with the highest incidence proportion of injuries were anterior compartment tendinopathy (19.4%), patellofemoral pain syndrome (15.8%), and Achilles tendinopathy (13.7%). The interpretation of epidemiological data in RRMIs is limited due to several methodological issues encountered.     

Increasing hip and knee flexion during a drop-jump task reduces tibiofemoral shear and compressive forces: implications for ACL injury prevention training

Although most ACL injury prevention programmes encourage greater hip and knee flexion during landing, it remains unknown how this technique influences tibiofemoral joint forces. We examined whether a landing strategy utilising greater hip and knee flexion decreases tibiofemoral anterior shear and compression. Twelve healthy women (25.9 ± 3.5 years) performed a drop-jump task before and after a training session (10–15 min) that emphasised greater hip and knee flexion. Peak tibiofemoral anterior shear and compressive forces were calculated using an electromyography (EMG)-driven knee model that incorporated joint kinematics, EMG and participant-specific muscle volumes and patella tendon orientation measured using magnetic resonance imaging (MRI). Participants demonstrated a decrease in peak anterior tibial shear forces (11.1 ± 3.3 vs. 9.6 ± 2.7 N · kg^?1; P = 0.008) and peak tibiofemoral compressive forces (68.4 ± 7.6 vs. 62.0 ± 5.5 N · kg^?1; P = 0.015) post-training. The decreased peak anterior tibial shear was accompanied by a decrease in the quadriceps anterior shear force, while the decreased peak compressive force was accompanied by decreased ground reaction force and hamstring forces. Our data provide justification for injury prevention programmes that encourage greater hip and knee flexion during landing to reduce tibiofemoral joint loading.     

Lack of association of the ACE genotype with the muscle strength response to resistance training

Abstract

Introduction: Previous studies have attempted to link the insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene with the variability in muscle strength responses to resistance training (RT); however, the literature is inconclusive. The purpose of the present study was to investigate the association between the ACE I/D genotype and muscle strength response to a RT program in young men.

Methods: 124 men (22±2.6 years; 174.8±6.5cm; 71.5±13.8 kg) without resistance training experience were tested before and after 11 weeks of five whole-body RT exercises (bench press, seated row, knee extension, knee flexion and sit ups). The bench press 1RM test was used to assess upper-body muscle strength and the isokinetic knee extensor peak torque (PT) was used as a measure of lower-body strength.

Results: At baseline, there were no differences among ACE genotype for 1RM load (54±11.7 kg for II, 58.5±8.9 kg for ID and 52.3±12.2 kg for DD) or knee extensor peak torque (PT) (220.1±36.8 N·m for II, 209.4 ±44.4 N·m for ID and 199.7±32.4 N·m for DD). Moreover, ACE genotype was not associated with lower-body (7.1±10.5%, 15.7±10.4% and 14.1±22.7% for II, ID and DD, respectively) or upper-body strength gains (16.2±8.9%, 14.5±11.3% and 21.9±17.1% for II, ID and DD, respectively) in response to RT.

Conclusion: The ACE I/D genotype was not associated with the muscle strength responses to RT.     

Changes in ankle joint stiffness due to stretching: The role of tendon elongation of the gastrocnemius muscle

Abstract

The purpose of this study was to investigate changes in ankle joint stiffness and the associated changes in the gastrocnemius muscle and tendon due to static stretching. Seven healthy male participants lay supine with the hip and knee joints fully extended. The right ankle joint was rotated into dorsiflexion from a 30° plantar flexed position and the torque measured by a dynamometer. The ankle joint was maintained in a dorsiflexed position for 20 min (static stretching of the calf muscles). We performed surface electromyography of the medial and lateral gastrocnemii, the soleus, and the tibialis anterior of the right leg to confirm no muscle activity throughout static stretching and the passive test (passive dorsiflexion). During static stretching, the ankle joint angle and elongation of the gastrocnemius were recorded by goniometry and ultrasonography, respectively. Tendon elongation of the gastrocnemius was calculated based on the changes in the ankle joint angle and muscle elongation. In addition, the relationships between passive torques and ankle joint angles, and elongation of muscle and tendon, were examined before and after static stretching. The ankle dorsiflexion angle and tendon elongation increased significantly by 10 min after the onset of static stretching, while there was no further increase in muscle length. In addition, ankle dorsiflexion angle and tendon elongation at an identical passive torque (30 N · m) increased significantly (from 24±7° to 33±5° and from 17±2 mm to 22±1 mm, respectively) after static stretching. However, muscle elongation was unchanged. In conclusion, the current results suggest that an increase in the ankle joint dorsiflexion angle due to static stretching is attributable to a change in tendon not muscle stiffness.     

Reliability of a combined biomechanical and surface electromyographical analysis system during dynamic barbell squat exercise

Abstract

An analysis system for barbell weightlifting exercises is proposed to record reliable performance and neuromuscular responses. The system consists of surface electromyography (sEMG) synchronized with electrogoniometry and a barbell position transducer. The purpose of this study was to establish the reliability of the three components of the system. Nine males (age 28.9 ± 4.8 years, mass 85.7 ± 15.1 kg) performed squat exercise at three loads on three separate trial days. A data acquisition and software system processed maximal knee angle (flexion), mean power for the concentric phase of squat exercise, and normalized root mean square of the vastus lateralis. Inter-trial coefficients of variation for each variable were calculated as 5.3%, 7.8%, and 7.5% respectively. In addition, knee joint motion and barbell displacement were significantly related to each other (bar displacement (m) = 1.39–0.0057 × knee angle (degress), with goodness-of-fit value, r ² = 0.817), suggesting knee goniometry alone can represent the kinematics of a multi-joint squat exercise. The proven reliability of the three components of this system allows for real-time monitoring of resistance exercise using the preferred training methods of athletes, which could be valuable in the understanding of the neuromuscular response of elite strength training methods.     

Specificity of a Maximal Step Exercise Test

To adhere to the principle of “exercise specificity” exercise testing should be completed using the same physical activity that is performed during exercise training. The present study was designed to assess whether aerobic step exercisers have a greater maximal oxygen consumption (max VO₂) when tested using an activity specific, maximal step exercise test (SET; arms and legs) versus a maximal running test (legs only). Female aerobic step exercisers (N=18; 20.7 ± 1.5 years) performed three maximal graded exercise tests (GXTs): 2 SETs; 1 treadmill test (TMT). The SET consisted of six 3-min progressive stages of alternate lead, basic step, basic step with biceps curls, knee raise with pull-down, repeater knee with pull-down, lateral lunge with pull-down, and side squat with shoulder presses. Stepping rate was 32 steps· min^?1 on an 8-in (20.32 cm) step for stages 1–3, and a 10-in (25.4 cm) step for stages 4–6. Submaximal and maximal heart rate (HR) and oxygen consumption (VO₂) were recorded at the end of each stage. Test–retest reliability for the first five stages of the SET ranged from .91 to .97 for HR, and from .84 to .96 for VO₂. Maximal HR was significantly greater (p =.0001) for the SET (200 ± 6.2 beats·min^?1) as compared to the TMT (193 ± 7.9 beats·min^?1). No significant difference was found for max VO₂ (42.9 ± 8.5, 41.2 ± 5.9 ml·kg^?1·min^?1, p =.14). The SET was a valid and reliable protocol for assessing responses of these aerobic step exercisers; however, max VO₂ from a TMT did not differ significantly from the SET. Conversely, max HR obtained from the criterion TMT was 7 beats·min^?1 lower than from the SET. If a training HR for step exercise (arms and legs exercise) is prescribed based on the max HR from treadmill exercise (legs only), then the training HR should be calculated from a TMT max HR that has been increased by 7 beats·min^?1 to obtain an intensity of step exercise comparable to that of running.     

The relationship between strength asymmetries and jumping performance in professional volleyball players

Knee peak torque (PT) is associated to jump performance in volleyball players. It is not clear whether muscle strength imbalances of the knee joint can influence jump performance. The purpose of study was to analyse the association between PT and knee muscular imbalances with jump performance in professional volleyball players. Eleven elite male volleyball players (90.3 ± 9.7 kg body mass and 1.94 ± 0.06 m height) were evaluated in an isokinetic dynamometer at speeds of 60, 180 and 300 deg/s. Muscle strength imbalances were obtained through calculation of contralateral deficit between limbs and the conventional ratio (hamstrings/quadriceps). Countermovement jump (CMJ) was performed on a force plate to calculate mechanical power and height. Association was found between knee extensor PT at 180 deg/s with CMJ power (r = 0.610, p = 0.046). Conventional ratio at 300 deg/s showed negative association with CMJ (r = ?0.656, p = 0.029). The optimal ratio between knee extensors PT in relation to the flexors PT is associated with the greater mechanical power in CMJ. Contralateral deficit does not seem to be associated with the CMJ performance. Considering the knee extensor PT is associated with CMJ power, our findings suggest that strength-based training in volleyball athletes should not omit the conventional muscle ratio.     

From the field of play to the laboratory: Recreating the demands of competition with augmented reality simulated sport

ABSTRACT

Biomechanical analysis has typically been confined to a laboratory setting. While attempts have been made to take laboratory testing into the field, this study was designed to assess whether augmented reality (AR) could be used to bring the field into the laboratory. This study aimed to measure knee load in volleyball players through a jump task incorporating AR while maintaining the perception-action couplings by replicating the visual features of a volleyball court. Twelve male volleyball athletes completed four tasks: drop landing, hop jump, spike jump, and spike jump while wearing AR smart glasses. Biomechanical variables included patellar tendon force, knee moment and kinematics of the ankle, knee, hip, pelvis and thorax. The drop landing showed differences in patellar tendon force and knee moment when compared to the other conditions. The hop jump did not present differences in kinetics when compared to the spike conditions, instead of displaying the greatest kinematic differences. As a measure of patellar tendon loading the AR condition showed a close approximation to the spike jump, with no differences present when comparing landing forces and mechanics. Thus, AR may be used in a clinical assessment to better replicate information from the competitive environment.     

前交叉韧带重建术后的康复训练

对前交叉韧带重建术后康复训练的文献进行分析研究,了解该领域的发展趋势。应用计算机检索Medline和Cnki1989—2006年间关于前交叉韧带相关文献。研究表明：股四头肌和胭绳肌肌力训练对膝关节功能恢复具有重要的作用,闭合运动链训练适合于康复训练早期,开放运动链训练适合于康复训练晚期;前交叉韧带损伤后,其本体感觉也受到破坏,而术后本体感觉促进训练对膝关节功能的完善至关重要;康复训练方案变得越来越激进,但激进的康复训练也有不利的一面,采用胭绳肌腱和异体肌腱重建前交叉韧带的术后康复训练应更趋于保守。     

The Effect of Initial Knee Angle on Concentric-Only Squat Jump Performance

Purpose: There is uncertainty as to which knee angle during a squat jump (SJ) produces maximal jump performance. Importantly, understanding this information will aid in determining appropriate ratios for assessment and monitoring of the explosive characteristics of athletes. Method: This study compared SJ performance across different knee angles—90º, 100º, 110º, 120º, 130º, and a self-selected depth—for jump height and other kinetic characteristics. For comparison between SJ and an unconstrained dynamic movement, participants also performed a countermovement jump from a self-selected depth. Thirteen participants (M_age = 25.4 ± 3.5 years, M_height = 1.8 ± 0.06 m, M_weight = 79.8 ± 9.5 kg) were recruited and tested for their SJ performance. Results: In the SJ, maximal jump height (35.4 ± 4.6 cm) was produced using a self-selected knee angle (98.7 ± 11.2°). Differences between 90°, 100°, and self-selected knee angles for jump height were trivial (ES ± 90% CL = 90°–100° 0.23 ± 0.12, 90°–SS ?0.04 ± 0.12, 100°–SS ?0.27 ± 0.20; 0.5–2.4 cm) and not statistically different. Differences between all other knee angles for jump height ranged from 3.8 ± 2.0 cm (mean ± 90% CL) to 16.6 ± 2.2 cm. A similar outcome to jump height was observed for velocity, force relative to body weight, and impulse for the assessed knee angles. Conclusions: For young physically active adult men, the use of a self-selected depth in the SJ results in optimal performance and has only a trivial difference to a constrained knee angle of either 90° or 100°.     

The effects of eccentric exercise-induced muscle damage on running kinematics at different speeds

Abstract

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 ± 2.8 years; 164 ± 8 cm; 53.6 ± 5.4 kg), performed a maximal eccentric muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60 rad · s^-1. Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48 h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3 m · s^-1). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5 m · s^-1. Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48 h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage.     

Correlation of axial impact forces with knee joint forces and kinematics during simulated ski-landing

Abstract

Anterior cruciate ligament (ACL) rupture, during ski-landing, is caused by excessive knee joint forces and kinematics, like anterior tibial translation, internal tibial rotation, and valgus rotation. It is not well understood how these forces/kinematics are directly related to ski-landing impact. In the present study, we applied simulated ski-landing impact to knee specimens, and examined joint force/kinematic responses and their correlations with impact force. Ten human cadaveric knees were subjected to axial impact loading at 70° of flexion to simulate ski-landing impact. Impact was repeated with incremental magnitude until ACL failure. Axial impact forces, anterior-posterior and medial-lateral tibial forces were measured using a tri-axial load cell. Anterior-posterior tibial translation, internal-external tibial rotation, and valgus-varus rotation were determined using a motion-capture system. We found positive correlations of axial impact force with anterior tibial force, medial tibial force, anterior tibial translation, internal tibial rotation, and valgus joint rotation. Axial impact forces were more strongly correlated with anterior tibial forces (R ² = 0.937 ± 0.050), anterior tibial translation (R ² = 0.916 ± 0.059), and internal tibial rotation (R ² = 0.831 ± 0.141) than medial tibial force (R ² = 0.677 ± 0.193) and valgus joint rotation (R ² = 0.630+0.271). During ski-landing, these joint forces/kinematics can synergistically act to increase ACL injury risk, whereby the failure mechanism would be dominated by anterior tibial forces, anterior tibial translation, and internal tibial rotation.     

Anthropometric dimensions of male powerlifters of varying body mass

Abstract

The aim of the study was to determine whether vibration applied directly to a muscle-tendon could enhance neuromuscular output during and 1.5 and 10 min after a bout of ballistic resistance training. Fourteen participants were exposed to two training conditions in random order: exercise with vibration and exercise with sham vibration. The exercise comprised three sets of ballistic knee extensions with a load of 60–70% of one-repetition maximum. Vibration (1.2 mm amplitude, 65 Hz frequency) was applied with a portable vibrator strapped over the distal tendon of the quadriceps. Knee joint angular velocity, moment, and power, and rectus femoris and vastus lateralis electromyography root-mean-squared were measured during knee extension. During and after training, the vibration did not induce significant changes in peak angular velocity, time to peak angular velocity, peak moment, time to peak moment, peak power, time to peak power, or average EMG of the rectus femoris and vastus lateralis. We conclude that direct vibration, at the selected amplitude and frequency, does not enhance these neuromuscular variables in ballistic knee extensions during or immediately after training.     

Effect of a preventive intervention programme on the prevalence of anterior knee pain in volleyball players

Abstract

Chronic knee disorders, such as patellofemoral pain syndrome and patellar tendinosis, are common injuries in volleyball players. Using a randomized clinical trial, the aim of the present study was to determine the effect of a 4-month in-season intervention programme on the prevalence of anterior knee pain in volleyball players. No significant differences were observed between the intervention and control group for the prevalence of anterior knee pain after the intervention programme (odds ratio =1.58 [95% confidence interval: 0.60–4.20]). Also, no significant differences were observed for individuals with previously sustained anterior knee pain (OR =0.81 [95% CI: 0.33–2.20]). It was revealed that the risk for recurrent anterior knee pain is significantly higher than the risk for newly sustained anterior knee pain (OR =5.79 [95% CI: 1.59–21.00]). In conclusion, we were unable to confirm any preventive effect of the intervention programme on the prevalence of anterior knee pain. However, a previous study using the same intervention and measuring the effect on the intrinsic risk factors of anterior knee pain showed a positive effect.     

Differences in impact characteristics,joint kinetics and measurement reliability between forehand and backhand forward badminton lunges

ABSTRACT

This study identified the effect of badminton lunging directions on impact characteristics, joint kinetics and measurement reliability. A total of 14 badminton players performed 20 lunges in both forehand and backhand sides. Ground reaction force (GRF) and three-dimensional joint moment variables were determined for further analyses. Paired t-tests and Wilcoxon signed-rank tests were performed to determine any differences between the two lunge directions and intra-class correlation (ICC) and sequential averaging analysis (SAA) were used to estimate the minimum number of trials. Compared to the forehand side, participants experienced significantly larger total GRF impulse (+ 3.8%, p = 0.021) and transverse moment (hip + 63.5%, p < 0.001; knee + 80.7%, p = 0.011), but smaller hip (?7.7%), knee (?18.7%) and ankle frontal moments (?58.0%, p < 0.05) in backhand lunges. The minimum number of trials was similar for both lunge directions, as the averaged absolute differences was less than one in both ICC and SAA. Furthermore, smaller minimal number of trials was determined by the ICC (7.9–8.0), compared with the SAA approach (9.5–10.3). Lunge direction would influence GRF and joint loading, but not on the measurement reliability. These results give important insights to establish performance or equipment evaluation protocols during badminton lunges.     

Muscle fatigue induced by exercise simulating the work rate of competitive soccer

Fatigue represents a reduction in the capability of muscle to generate force. The aim of the present study was to establish the effects of exercise that simulates the work rate of competitive soccer players on the strength of the knee extensors and knee flexors. Thirteen amateur soccer players (age 23.3±3.9 years, height 1.78±0.05?m, body mass 74.8±3.6?kg; mean±s) were tested during the 2000–2001 soccer season. Muscle strength of the quadriceps and hamstrings was measured on an isokinetic dynamometer. A 90?min soccer-specific intermittent exercise protocol, incorporating a 15?min half-time intermission, was developed to provide fatiguing exercise corresponding in work rate to a game of soccer. The exercise protocol, performed on a programmable motorized treadmill, consisted of the different intensities observed during soccer match-play (e.g. walking, jogging, running, sprinting). Muscle strength was assessed before exercise, at half-time and immediately after exercise. A repeated-measures analysis of variance showed significant reductions (P?<0.001) in peak torque for both the quadriceps and hamstrings at all angular velocities (concentric: 1.05, 2.09, 5.23 rad?·?s^?1; eccentric: 2.09 rad?·?s^?1). The peak torque of the knee extensors (KE) and knee flexors (KF) was greater before exercise [KE: 232±37, 182±34, 129±27, 219±41?N?·?m at 1.05, 2.09 and 5.23 rad?·?s^?1 (concentric) and 2.09 rad?·?s^?1 (eccentric), respectively; KF: 126±20, 112±19, 101±16, 137±23?N?·?m] than at half-time (KE: 209±45, 177±35, 125±36, 214±43?N?·?m; KF: 114±31, 102±20, 92±15, 125±25?N?·?m) and greater at half-time than after exercise (KE: 196±43, 167±35, 118±24, 204±43?N?·?m; KF: 104±25, 95±21, 87±13, 114±27?N?·?m). For the hamstrings?:?quadriceps ratio, significant changes were found (P?<0.05) for both legs, the ratio being greater before than after exercise. For fast?:?slow speed and left?:?right ratios, no significant changes were found. We conclude that there is a progressive reduction in muscle strength that applies across a range of functional characteristics during exercise that mimics the work rate in soccer.