Alterations in peripheral muscle contractile characteristics following high and low intensity bouts of exercise.

The aim of this study was to monitor muscle contractile performance in vivo, using an electrical stimulation protocol, immediately following an acute high and low intensity exercise session conducted at the same average intensity performed on a cycle ergometer. Eighteen healthy males (25.1 ± 4.5 years, 81.6 ± 9.8 kg, 1.83 ± 0.06 m; mean ± SD) participated in the study. On two occasions, separated by 1 week, subjects completed a high and low intensity exercise session in a random order on a cycle ergometer, performing equal total work in each. At the end of each test, a muscle performance test using electrical stimulation was performed within 120 s. Post-exercise muscle data were compared to the subjects' rested muscle. We found a reduction in muscle contractile performance following both high and low intensity exercise protocols but a greater reduction in maximal voluntary contraction (MVC) (P < 0.01), rate of torque development (RTD) (P < 0.001), rate of relaxation (RR(½)), (P < 0.001) the 60 s slope of the fatigue protocol (P < 0.01) and torque frequency response (P < 0.05) following the high intensity bout. Importantly muscle performance remained reduced 1 h following high intensity exercise but was recovered following low intensity exercise. Muscle function was significantly reduced following higher intensity intermittent exercise in comparison to lower intensity exercise even when the average overall intensity was the same. This study is the first to demonstrate the sensitivity of muscle contractile characteristics to different exercise intensities and the impact of higher intensity bursts on muscle performance.

Muscle contractile characteristics: relationship to high-intensity exercise.

We investigated the relationship between muscle contractile characteristics, collected using percutaneous electrical stimulation, and high-intensity exercise performance. Seventeen participants performed a muscle performance test for the calculation of rate of torque development (RTD), rate of relaxation (RR(1/2)), rate of fatigue and fatigue resistance. On a second visit the participants completed a Wingate cycle ergometer test with peak power, mean power, fatigue index and fatigue rate calculated. The muscle fatigue index related significantly to the WAnT fatigue index and fatigue rate (p < 0.01). The change in rate of torque development (%DeltaRTD) was also related significantly to the fatigue rate (W/s) during the WAnT. Subjects displaying the greatest reduction in RTD had the greatest fatigue rate during the WAnT and greater fatigue during the electrical stimulation protocol. There were no significant relationships between peak (r 0.36; p > 0.01) or mean power (r -0.11, p > 0.01) with any of the muscle performance measures. These findings demonstrate that muscle contractile characteristics, elicited during standardised in vivo electrical stimulation, relate to performance during a Wingate anaerobic test. They suggest that muscle contraction characteristics play an important role in high-intensity exercise performance and indicate that electrical stimulation protocols can be a useful additional tool to explore muscle contraction characteristics in relation to exercise performance and trainability.

Effectiveness of a community-based low intensity exercise programme for ambulatory stroke survivors.

PURPOSE: To establish the feasibility and effectiveness of a community-based exercise programme for ambulatory patients with stroke discharged from rehabilitation. METHOD: Eighteen participants were recruited 3-12 months after onset of first stroke. Using a time series experimental design, the group completed a baseline period of 4 weeks (A1), a group exercise programme of low-intensity progressive resistive exercise and functional tasks for lower limb muscles (B) and repeat assessment after cessation of exercise (A2). Fitness instructors delivered sessions at Leisure Centres twice weekly for 14 weeks with physiotherapy support and the minimum attendance requirement was 16 sessions. Measures included muscle strength, gait velocity, Berg Balance Scale and Nottingham Extended Activities of Daily Living. RESULTS: Lower limb muscle strength improved after training (ANOVA, p < 0.02). Paretic knee extension strength increased from 43.4 + or - 5.9 to 60.4 + or - 6.8 Nm after 16 exercise sessions. Walking velocity increased significantly (ANOVA, p < 0.001), from 0.54 + or - 0.07 to 0.75 + or - 0.08 m/s (t = -3.31, p < 0.01). Balance and everyday function were also significantly improved (p < 0.003). There were marked individual variation in the response to training, and those who completed additional training did not show benefit. CONCLUSIONS: This community-based exercise programme was feasible and delivered positive improvements in physical function for participants. Further issues raised for investigation include the individual response to training and the benefits of extended training.

Relationships between muscle fatigue characteristics and markers of endurance performance.

The aim of this study was to examine the relationship of a range of in-vivo whole muscle characteristics to determinants of endurance performance. Eleven healthy males completed a cycle ergometer step test to exhaustion for the determination of the lactate threshold, gross mechanical efficiency, peak power and VO2max. On two separate occasions, contractile and fatigue characteristics of the quadriceps femoris were collected using a specially designed isometric strength-testing chair. Muscle fatigue was then assessed by stimulating the muscle for 3 minutes. Force, rate of force development and rates of relaxation were calculated at the beginning and end of the 3 minute protocol and examined for reliability and in relation to lactate threshold, VO2max, gross mechanical efficiency and peak power. Muscle characteristics, rate of force development and relaxation rate were demonstrated to be reliable measures. Force drop off over the 3 minutes (fatigue index) was related to lactate threshold (r = -0.72 p » 0.01) but not to VO2max. The rate of force development related to the peak power at the end of the cycle ergometer test (r = -0.75 p » 0.01). Rates of relaxation did not relate to any of the performance markers. We found in-vivo whole muscle characteristics, such as the fatigue index and rate of force development, relate to specific markers of peripheral, but not to central, fitness components. Our investigation suggests that muscle characteristics assessed in this way is reliable and could be feasibly utilised to further our understanding of the peripheral factors underpinning performance. Key pointsParticipants with a high lactate threshold displayed greater fatigue resistance in the electrical stimulation test.Muscle performance characteristics relate to specific components of endurance performance.The electrical stimulation protocol could be a useful technique, alongside other established measures, when constructing a physiological profile of a participant.

Hip, knee, ankle kinematics and kinetics during stair ascent and descent in healthy young individuals.

BACKGROUND: Few studies have reported the biomechanical aspects of stair climbing for this ergonomically demanding task. The purpose of this ethically approved study was to identify normal functional parameters of the lower limb during stair climbing and to compare the actions of stair ascent and descent in young healthy individuals. METHODS: Thirty-three young healthy subjects, (16 M, 17 F, range 18-39 years) participated in the study. The laboratory staircase consisted of four steps (rise height 18 cm, tread length 28.5 cm). Kinematic data were recorded using 3D motion analysis system. Temporal gait cycle data and ground reaction forces were recorded using a force platform. Kinetic data were standardized to body mass and height. FINDINGS: Paired-samples t tests showed significantly greater hip and knee angles (mean difference standard deviation (SD): hip 28.10 degrees (SD 4.08), knee 3.39 degrees (SD 7.20)) and hip and knee moments (hip 0.25 Nm/kg (SD 0.18), knee 0.17 Nm/kg (SD 0.15)) during stair ascent compared to descent. Significantly greater ankle dorsiflexion angles (9.90 degrees (SD 3.80)) and plantarflexion angles (8.78 degrees (SD 4.80)) were found during stair descent compared to ascent. Coefficient of variation (mean (SD)) in percentage between repeated tests varied for joint angles and moments, respectively (2.35% (SD 1.83)-17.53% (SD 13.62)) and (4.65% (SD 2.99)-40.73% (SD 24.77)). INTERPRETATION: Stair ascent was shown to be the more demanding biomechanical task when compared to stair descent for healthy young subjects. The findings from the current study provide baseline measures for pathological studies, theoretical joint modelling, and for mechanical joint simulators.

Exertional symptoms and exercise capacity in individuals with brain injury.

PURPOSE: To examine factors affecting cycling exercise performance in individuals with acquired brain injury. METHODS: Thirty individuals with acquired brain injury and 18 sedentary controls (SC) participated. Heart rate, bicycle power output and rating of perceived exertional (RPE) were recorded, throughout incremental cycle ergometer exercise. The SC group and 18 moderately impaired individuals from the ABI group performed a 25-W (B25) protocol. The remaining 12 individuals performed a 10-W protocol (B10). RESULTS: The B10 group terminated exercise at the lowest RPE, percentage age predicted maximal heart rate (% APMHR) and bicycle power output, followed by the B25 and then the SC group (RPE: Kruskal - Wallis test P < 0.001, %APMHR and bicycle power output: one-way ANOVA P < 0.01). RPE was correlated with %APMHR and percentage of peak bicycle output (B10 group: R2 0.1 to 0.67; B25 group: 0.69 - 0.83; SC group: 0.76 - 0.91). There was no difference in RPE at the same relative work intensity between the B25 and the sedentary control group (P > 0.05). Forward regression analysis revealed fatigue levels were predictive of %APMHR at test termination (beta = -0.411, P < 0.05) and quadriceps strength was predictive of peak bicycle power output (beta = 0.612, P < 0.05). CONCLUSIONS: Individuals with brain injury terminated exercise at lower exercise intensities but rated exertion no differently from healthy individuals. General fatigue levels predicted %APMHR and quadriceps strength predicted peak bicycle power output.

Biomechanics of lower limb haemophilic arthropathy.

Intermittent joint bleeding and potential arthropathy remain a concern for patients and those responsible for haemophilic care. Monitoring the status of haemophilic joints is a current challenge. Evaluation of bone and soft tissue with radiological imaging together with clinical joint scoring is often used to monitor haemophilic arthropathy and may not be sufficiently sensitive to early changes in joint morphology. Recently an interest in the biomechanical status of haemophilic joints has emerged. Biomechanics is defined as the interdiscipline that describes, analyses and assesses movement in relation to biological and physical principles. This review considers the biomechanical evaluation of haemophilic joint status of the lower limb with particular reference to the evaluation of muscle atrophy, muscle strength, range of motion and gait as well as the relationship to haemophilic arthropathy. In raising the need for increased clinical awareness, this review highlights the need to establish test-retest and inter-rater reliability and ensuring that comparative studies are undertaken with age-matched unaffected peer groups.

Changes in muscle strength and EMG median frequency after anterior cruciate ligament reconstruction.

The purpose of this study was to monitor neuromuscular changes in quadriceps femoris muscle at 1 and 3 months after anterior cruciate ligament reconstruction (ACLR). Changes in isometric muscle strength (MVC), voluntary activation and surface electromyogram (EMG) parameters were examined in relation to knee stability, pain and swelling in 31 patients (25 M, 6 F) mean (SD) 30(8) years. Physically inactive (RC) and sports participants (SC) acted as controls. Median frequency (Hz) and amplitude (mV) of rectus femoris using Fast Fourier Transform (FFT) 2(11) was calculated during 5-s isometric contractions at 100, 75, 50 and 25% of MVC. One month after surgery, a significant correlation (P < 0.01) was found between activation (%) and MVC of injured knee extensors. By 3 months, most patients were pain free and had achieved full activation but still had muscle weakness. At 1 and 3 months post-surgery and for all levels of MVC contraction, the median frequencies of the injured limbs were significantly lower (P < 0.05) compared to the SC group as were those of the RC group. There was a significant lowering of the median frequencies of the uninjured limbs compared to the SC group at 75 and 100% of MVC. The EMG amplitude of the uninjured and injured limbs mirrored those of the SC and RC groups, respectively. These results support the view that muscle activation patterns were altered following ACL injury and surgical repair and may contribute to subsequent changes in muscle fibre properties during detraining and subsequent retraining.

Borg's rating of perceived exertion scales: do the verbal anchors mean the same for different clinical groups?

OBJECTIVE: To examine the interpretation of the verbal anchors used in the Borg rating of perceived exertion (RPE) scales in different clinical groups and a healthy control group. DESIGN: Prospective experimental study. SETTING: Rehabilitation center. PARTICIPANTS: Nineteen subjects with brain injury, 16 with chronic low back pain (CLBP), and 20 healthy controls. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Subjects used a visual analog scale (VAS) to rate their interpretation of the verbal anchors from the Borg RPE 6-20 and the newer 10-point category ratio scale. RESULTS: All groups placed the verbal anchors in the order that they occur on the scales. There were significant within-group differences ( P >.05) between VAS scores for 4 verbal anchors in the control group, 8 in the CLBP group, and 2 in the brain injury group. There was no significant difference in rating of each verbal anchor between the groups ( P >.05). CONCLUSIONS: All subjects rated the verbal anchors in the order they occur on the scales, but there was less agreement in rating of each verbal anchor among subjects in the brain injury group. Clinicians should consider the possibility of small discrepancies in the meaning of the verbal anchors to subjects, particularly those recovering from brain injury, when they evaluate exercise perceptions.

The effect of a perceptual cognitive task on exercise performance: the dual-task condition after brain injury.

OBJECTIVE: To examine the effect of additional cognitive demand on cycling performance in individuals with acquired brain injury (ABI). DESIGN: Prospective observational study. SETTING: Rivermead Rehabilitation Centre. PARTICIPANTS: Ten individuals with ABI (7 men, 3 women) (traumatic brain injury 7, tumour 1, stroke 2) and 10 healthy controls (6 men, 4 women). INTERVENTION: Individuals were asked to maintain a set cadence during a three-stage incremental cycling test in both single-task (no additional task) and dual-task (whilst performing an additional cognitive task) conditions. RESULTS: The ABI group showed a slight slowing in cadence in stages 1 and 3 of the graded exercise test from the single- to the dual-task condition, although this was not significant (p < or = 0.05). The control group showed no slowing of cadence at any incremental stage. When directly comparing the ABI with the control group, the change in cadence observed in dual-task conditions was only significantly different in stage 3 (p < or = 0.05). CONCLUSIONS: Clinicians should be aware of the possibility that giving additional cognitive tasks (such as monitoring exercise intensity) while individuals with acquired brain injury are performing exercises may detrimentally affect performance. The effect may be more marked when the individuals are performing exercise at higher intensities.

The effect of increasing effort on movement economy during incremental cycling exercise in individuals early after acquired brain injury.

OBJECTIVE: To investigate the effect of increasing effort on energy cost as measured by oxygen consumption (VO2) during cycling exercise in individuals early after acquired brain injury (ABI). DESIGN: An experimental correlation design. SETTING: Specialist neurorehabilitation centre. PARTICIPANTS: Thirty-eight individuals were recruited early after acquired brain injury. Nine individuals had spasticity; Ashworth Scale >1 in either upper or lower limbs. INTERVENTION: The VO2 was measured in relation to workload during a graded exercise test. RESULTS: The VO2 increased in a linear fashion with increases in workload in 34 individuals. Only one individual with spasticity demonstrated a nonlinear relationship. CONCLUSION: Increasing the workload during cycling exercise does not disproportionately increase energy cost in most individuals with spasticity early after ABI.