Acute fatigue negatively affects risk factors for injury in trained but not well-trained habitually shod runners when running barefoot.

INTRODUCTION: Many factors may contribute to running-related injury. These include fatigue and footwear, the combination of which has rarely been studied, in particular with reference to barefoot running, recently advocated as a method to reduce injury risk. METHODS: Twenty-two runners (12 well-trained and 10 trained) participated in a 10 km fatiguing trial. Knee and ankle joint kinematics and kinetics and electromyography were assessed during overground running in the barefoot and shod condition. This was performed pre- and post-fatigue using a motion capture system and force platforms. RESULTS: Initial loading rate increased in the trained runners when barefoot but not shod. Shod knee stiffness increased in both groups after fatigue, whereas barefoot knee stiffness decreased only in the trained group. A reduction in barefoot bicep femoris pre-activation was found in both groups. During stance, a reduction in vastus lateralis and biceps femoris and an increase in tibialis anterior activity were found over time in both groups and conditions. Trained runners decreased gluteus medius and increased lateral gastrocnemius median frequency for both conditions after fatigue. CONCLUSION: When fatigued, gait adjustments in habitually shod runners may increase injury risk when running barefoot. Training status may be a risk factor for injury, as less-trained runners experience muscular fatigue changes that may compromise ground reaction force attenuation. Caution is recommended when transitioning to pure barefoot running.

Site-Specific Bone Mineral Density Is Unaltered Despite Differences in Fat-Free Soft Tissue Mass Between Affected and Nonaffected Sides in Hemiplegic Paralympic Athletes with Cerebral Palsy: Preliminary Findings.

OBJECTIVE: This study investigated bone mineral density (BMD, g/cm), fat mass (FM, kg), and fat-free soft tissue mass (FFSTM, kg) in Paralympic athletes with cerebral palsy (CP) using dual-energy x-ray absorptiometry. METHODS: Bone mineral density, BMD Z scores (standard deviations), FM, and FFSTM were measured for the whole body and at the lumbar spine, femoral neck, and total hip sites on both nonaffected and affected sides of 6 athletes with hemiplegic CP. RESULTS: There were no differences between nonaffected and affected sides with respect to site-specific BMD and BMD Z scores and FM. Fat-free soft tissue mass was significantly lower on the affected side in both upper and lower limbs (15% lower; P < 0.05). CONCLUSION: The present study is the first to describe similar BMD between sides, symmetry in FM, and asymmetry in FFSTM in Paralympic athletes with CP. These findings have important consequences for rehabilitation, as they indicate the potential for positive physiological adaptation as a result of exercise training over long periods of time.

Effects of Induced Volitional Fatigue on Sprint and Jump Performance in Paralympic Athletes with Cerebral Palsy.

OBJECTIVE: This study investigated performance, neuromuscular characteristics, and fatigue in Paralympic athletes with cerebral palsy (CP) during a maximal explosive performance trial, compared with well-trained, sprint-specific able-bodied athletes. DESIGN: Six Paralympic athletes with hemiplegic CP and 12 able-bodied athletes performed one 40-m sprint test (in seconds) and Vertical Jump Tests off both legs (in centimeters), the affected leg individually (in centimeters), and the nonaffected leg individually (in centimeters) before and after an adapted Multistage Shuttle Run Test to exhaustion. Electromyography of five bilateral muscles was measured for mean amplitude (percentage maximum activation). RESULTS: The 40-m sprint test, Vertical Jump Test off both legs, and Vertical Jump Test off the affected leg were significantly compromised in the CP group, whereas the Vertical Jump Test off the nonaffected leg was similar between groups (P < 0.05). Both groups fatigued similarly in performance and electromyography. Affected side electromyography was higher than nonaffected electromyography in the Vertical Jump Test off both legs and Vertical Jump Test off the affected leg in both groups. CONCLUSIONS: The similarity in fatigue between CP and able-bodied groups confirms that Paralympic athletes with CP may have overcome deficits associated with CP documented in sedentary children. The identified asymmetry may assist with a deeper understanding of performance deficits in CP, as it is indicated that activity generated by both legs is performed toward the capacity of the affected leg.

A descriptive comparison of sprint cycling performance and neuromuscular characteristics in able-bodied athletes and paralympic athletes with cerebral palsy.

OBJECTIVE: This study investigated the sprint cycling performance and neuromuscular characteristics of Paralympic athletes with cerebral palsy (CP) during a fatiguing maximal cycling trial compared with those of able-bodied (AB) athletes. DESIGN: Five elite athletes with CP and 16 AB age- and performance-matched controls performed a 30-sec Wingate cycle test. Power output (W/kg) and fatigue index (%) were calculated. Electromyography was measured in five bilateral muscles and expressed in mean amplitude (mV) and median frequency (Hz). RESULTS: Power output was significantly higher in the AB group (10.4 [0.5] W/kg) than in the CP group (9.8 [0.5] W/kg) (P < 0.05). Fatigue index was statistically similar between the AB (27% [0.1%]) and CP (25% [0.1%]) groups. Electromyographic mean amplitude and frequency changed similarly in all muscle groups tested, in both affected and nonaffected sides, in the CP and AB groups (P < 0.05). Neuromuscular irregularities were identified in the CP group. CONCLUSIONS: The similarity in fatigue between the CP and AB groups indicates that elite athletes with CP may have a different exercise response to others with CP. The authors propose that this may result from high-level training over many years. This has rehabilitative implications, as it indicates near-maximal adaptation of the CP body toward normal levels.

The effect of exercise induced hyperthermia on muscle fibre conduction velocity during sustained isometric contraction.

This study investigated the effect of dynamic exercise in a hot environment on muscle fibre conduction velocity (MFCV) of the knee extensors during a sustained isometric contraction. Seven trained male cyclists (mean [±SD], age, and V˙O(2max) were 35±9.9 and 57.4±6.6 ml kg(-1) min(-1)) cycled for 50 min at 60% of peak power output in either: (1) 40°C (HOT); or (2) 19°C (NEUTRO); and (3) remained passive in 40°C (PASS). Post-intervention a 100 s maximal sustained isometric contraction (SMC) of the knee extensors was performed. Rectal temperature increased (p<0.01) for both HOT and NEUTRO with PASS unchanged and with HOT rising higher (p<0.01) than NEUTRO (38.6±0.4 vs. 37.6±0.4°C). Muscle temperature increased (p<0.01) for all three conditions with HOT rising the highest (p<0.01) (40.3±0.5 vs. 38.3±0.3 and 37.6±1.3°C for NEUTRO and PASS, respectively). Lactate showed higher accumulation (p<0.01) for HOT than NEUTRO (6.9±2.3 vs. 4.2±2.1 mmol l(-1)). During SMC the torque, electromyography root mean squared (RMS) and MFCV all significantly (p<0.01) declined. Only in HOT did MFCV decline significantly (p<0.01) less than torque and RMS (9.9±6.2% vs. 37.5±17.8% and 37.6±21.4%, respectively). In conclusion, during exercise induced hyperthermia, reduced motor unit recruitment as opposed to slower conducting properties of the muscle fibre appears to be responsible for the greater reduction in torque output.

Alternative methods of normalising EMG during running.

We evaluated possible methods of normalising EMG measured during running. MVC, Sprint and 70% Peak Running Speed methods were evaluated and their repeatability, reliability and sensitivity to incremental running speed were compared. Twelve runners performed the same experimental protocol on three separate occasions. Each day, subjects firstly performed MVCs, followed by a 20 m maximal sprint (with a 20-30 m run-up). Following this, they performed the peak running speed (PRS) test until exhaustion. After which they ran at 70% of PRS for 5 laps. Results indicated that normalising EMG data to MVC and Sprint methods are more repeatable for VM, BF, MG and RF, VL, LG, respectively, with the average ICC>0.80. The 70% PRS demonstrated poor to fair levels of repeatability ranging between ICC 0.27 and 0.70. Whereas the 70% PRS method had the least intra-subject variability and the greatest sensitivity to increasing running speeds. More specifically, demonstrating significant changes in muscle activity in VM with increasing running speed while MVC and Sprint methods were unable to detect these changes. The dynamic methods were the most appropriate for EMG normalisation showing repeatability, better intra-subject reliability and better sensitivity during running over different days and for once-off measurements.

Alternative methods of normalising EMG during cycling.

We evaluated possible methods of normalisation for EMG measured during cycling. The MVC method, Sprint method and 70% Peak Power Output Method were investigated and their repeatability, reliability and sensitivity to change in workload were compared. Thirteen cyclists performed the same experimental protocol on three separate occasions. Each day, subjects firstly performed MVCs, followed by a 10s maximal sprint on a cycle ergometer. Subjects then performed a Peak Power Output (PPO) test until exhaustion. After which they cycled at 70% of PPO for 5 min at 90 rpm. Results indicated that normalising EMG data to 70% PPO is more repeatable, the intra-class correlation (ICC) of 70% PPO (0.87) was significantly higher than for MVC (0.66) (p=0.03) and 10s sprint (0.65) (p=0.04). The 70% PPO method also demonstrated the least intra-subject variability for five out of the six muscles. The Sprint and 70% PPO method highlighted greater sensitivity to changes in muscle activity than the MVC method. The MVC method showed the highest intra-subject variability for most muscles except VM. The data suggests that normalising EMG to dynamic methods is the most appropriate for examining muscle activity during cycling over different days and for once-off measurements.