Is repetition failure critical for the development of muscle hypertrophy and strength?

This investigation sought to determine the effect of resistance training to failure on functional, structural and neural elbow flexor muscle adaptation. Twenty-eight males completed a 4-week familiarization period and were then counterbalanced on the basis of responsiveness across; non-failure rapid shortening (RS; rapid concentric, 2 s eccentric), non-failure stretch-shortening (SSC; rapid concentric, rapid eccentric), and failure control (C, 2 s concentric, 2 s eccentric), for a 12-week unilateral elbow flexor resistance training regimen, 3 × week using 85% of one repetition maximum (1RM). 1RM, maximal voluntary contraction (MVC), muscle cross-sectional area (CSA), and muscle activation (EMG(RMS)) of the agonist, antagonist, and stabilizer muscles were assessed before and after the 12-week training period. The average number of repetitions per set was significantly lower in RS 4.2 [confidence interval (CI): 4.2, 4.3] and SSC 4.2 (CI: 4.2, 4.3) compared with C 6.1 (CI: 5.8, 6.4). A significant increase in 1RM (30.5%), MVC (13.3%), CSA (11.4%), and agonist EMG(RMS) (22.1%) was observed; however, no between-group differences were detected. In contrast, antagonist EMG(RMS) increased significantly in SSC (40.5%) and C (23.3%), but decreased in RS (13.5%). Similar adaptations across the three resistance training regimen suggest repetition failure is not critical to elicit significant neural and structural changes to skeletal muscle.

Does intramuscular thermal feedback modulate eccrine sweating in exercising humans?

AIM: Few investigators have considered the possibility that skeletal muscles might contain thermosensitive elements capable of modifying thermoeffector responses. In this experiment, the temporal relationships between dynamic changes in deep-body and intramuscular temperatures and eccrine sweat secretion were explored during rhythmical and reproducible variations in heat production. METHODS: Eight subjects performed semi-recumbent cycling (25 °C) at a constant load to first establish whole-body thermal and sudomotor steady states (35 min), followed by a 24-min block of sinusoidal workload variations (three, 8-min periods) and then returning to steady-state cycling (20 min). Individual oesophageal, mean skin and intramuscular (vastus lateralis) temperatures were independently cross-correlated with simultaneously measured forehead sweat rates to evaluate the possible thermal modulation of sudomotor activity. RESULTS: Both intramuscular and oesophageal temperatures showed strong correlations with sinusoidal variations in sweating with respective maximal cross-correlation coefficients of 0.807 (±0.044) and 0.845 (±0.035), but these were not different (P = 0.40). However, the phase delay between intramuscular temperature changes and sweat secretion was significantly shorter than the delay between oesophageal temperature and sweating [25.6 s (±12.6) vs. 46.9 s (±11.3); P = 0.03]. CONCLUSION: The temporal coupling of eccrine sweating to intramuscular temperature, combined with a shorter phase delay, was consistent with the presence of thermosensitive elements within skeletal muscles that appear to participate in the modulation of thermal sweating.

Short-duration fatigue alters neuromuscular coordination of trunk musculature: implications for injury.

The aim of this investigation was to determine the effect of muscle fatigue, produced by two different fatigue protocols, on the coordination of trunk and thigh muscles during the performance of a manual-handling task (e.g. a weighted stoop lift). The two fatigue protocols were designed to produce either (a) a non-specific widespread fatigue of trunk and limb muscles (e.g. rowing fatigue protocol), or (b) a specific fatigue of the trunk extensor musculature (e.g. back extension fatigue protocol). Specifically, we wished to determine whether the coordination of trunk muscles during a stoop lift was compromised more, or less, by either of these two fatigue protocols. Ten male subjects (20-24 years) were tested utilising an electromyographic technique which collected electromyograms from trunk flexor and extensor muscles, as well as the Hamstring muscle group, during a pre- and a post-fatigue performance of a weighted stoop lift. The results showed that the back extension fatigue protocol, but not the rowing fatigue protocol, produced significant (p<0.05) changes in the timing of trunk muscle activation during a stoop lift. The longer periods of muscle activation seen only after the back extension fatigue protocol, suggested that fatigue of these muscles had required the CNS to alter their periods of activation to a pattern similar to that previously seen in elderly populations. The results also suggested that intense short-duration motor tasks, which may differentially target the back and its musculature, could leave the spine susceptible to increased risk of injury even though worker perceptions of general fatigue are low. Risk assessment guidelines for manual handling should consider not only the weight and frequency of the lift, but lift duration as well to maintain worker safety.

Does fatigue induced by repeated dynamic efforts affect hamstring muscle function?

PURPOSE: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. METHODS: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects' sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded. RESULTS: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects' running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride. CONCLUSIONS: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.

Carotid baroreflex control of heart rate and blood pressure during ES leg cycling in paraplegics.

This study investigated control of heart rate (HR) and mean arterial pressure (MAP) at rest and during electrical stimulation (ES) leg cycling exercise (LCE) in paraplegics (Para). Seven men with complete spinal lesions (T(5)-T(11)) and six able-bodied (AB) men participated in this study. Beat-to-beat changes in HR and MAP were recorded during carotid sinus perturbation. Carotid baroreflex function curves were derived at rest and during ES-LCE for Para and during voluntary cycling (Vol) for AB. From rest to ES-LCE, oxygen uptake (VO(2)) increased (by 0.43 l/min) and HR rose (by 11 beats/min), yet MAP remained unchanged. In AB, Vol increased VO(2) (by 0.53 l/min), HR (by 22 beats/min), and MAP (by 8 mmHg). ES-LCE did not alter the carotid sinus pressure (CSP)-MAP relationship, but it displaced the CSP-HR relationship upward relative to rest. No rightward shift was observed during ES-LCE. Vol by AB produced an upward and rightward displacement of the CSP-MAP and CSP-HR relationships relative to rest. These findings suggested that the carotid sinus baroreflex was not reset during ES-LCE in Para.

Parkinson's disease: an investigation of exercise capacity, respiratory function, and gait.

OBJECTIVE: To evaluate the exercise capacity of subjects with mild to moderate Parkinson's disease and determine whether abnormalities in respiratory function and gait affect exercise capacity. DESIGN: Descriptive. Subjects were categorized according to exercise history, disease severity, and presence/absence of upper airway obstruction. SUBJECTS AND SETTING: Sixteen volunteers with mild to moderate idiopathic Parkinson's disease attended a university research laboratory. MAIN OUTCOME MEASURES: Subjects performed a maximum exercise test on a cycle ergometer, together with respiratory function tests and a walking test. Peak values for oxygen consumption and work rate were recorded for the maximum exercise test. Measures of respiratory function included spirometry, flow-volume loops, lung volumes, and mouth pressures. Velocity, stride length, and cadence were measured for preferred and fast speeds of walking. The values obtained on each of these tests were compared with published predicted age- and gender-matched normal values. RESULTS: Peak oxygen consumptions and peak work loads achieved by subjects with Parkinson's disease were not significantly different from normal values, despite evidence of respiratory and gait abnormalities typical of Parkinson's disease. Exercise category was significantly correlated with percent predicted VO2peak (r = .64, p < .01), with sedentary subjects producing lower scores than exercising subjects. There was no significant correlation between disease severity and percent predicted VO2peak. CONCLUSION: Despite their neurological deficit, individuals with mild to moderate Parkinson's disease have the potential to maintain normal exercise capacity with regular aerobic exercise.