Search results for "Muscle Contraction"
showing 10 items of 569 documents
Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women.
1996
Twelve middle-aged men and 12 middle-aged women in the 50-year-old age group (M50; range 44-57 years; W50; 43-57), and 12 elderly men and 12 elderly women in the 70-year-old age group (M70; 59-75; W70; 62-75) volunteered as subjects in order to examine effects of 12-week progressive heavy resistance strength training on electromyographic activity (EMG), muscle cross-sectional area (CSA) of the quadriceps femoris and maximal concentric force in a one repetition maximum (1 RM) test of the knee extensor muscles. One half of the subjects in each group performed the knee extension (and flexion) exercises only bilaterally (BIL), while another half performed the exercises only unilaterally (UNIL).…
Responses of serum androgenic-anabolic and catabolic hormones to prolonged strength training.
1988
Endocrine and neuromuscular effects of prolonged strength training were investigated in 21 strength-trained male subjects during the course of a 24-week progressive strength training and during a subsequent detraining period of 12 weeks. Maximal isometric leg extensor force increased by 19% (P less than 0.001) during the first 20 weeks, followed by a plateau during the 4 latest weeks of training. During the course of the training period, no systematic change was found in serum testosterone concentrations, but there was a decreasing tendency in the concentrations of free testosterone (NS), 17-OH-progesterone (NS), androstenedione (P less than 0.05), dehydroepiandrosterone (P less than 0.05),…
Acute hormonal responses to heavy resistance exercise in strength athletes versus nonathletes.
2004
The aim of the present study was to investigate acute hormonal and neuromuscular responses and recovery in strength athletes versus nonathletes during heavy resistance exercise performed with the forced and maximum repetitions training protocol. Eight male strength athletes (SA) with several years of continuous resistance training experience and 8 physically active but non-strength athletes (NA) volunteered as subjects. The experimental design comprised two loading sessions: maximum repetitions (MR) and forced repetitions (FR). MR included 12-RM squats for 4 sets with a 2-min recovery between sets. In FR the initial load was higher than in MR so that the subject could lift approximately 8 …
Adaptive response of human skeletal muscle to simulated hypergravity condition
1985
The mechanical behaviour of leg extensor muscles of five international-level athletes was evaluated during 13 months training period. Drop jumps, average mechanical power during 15 S continuous jump, and vertical jumps performed with and without extra weights were used to measure explosive power characteristics. The data recorded in vertical jumps was utilized for construction of force-velocity relationship (F-V curve). The athletes did not show improvement in any of the variables studied after 12 months of intensive systematic training programme. It was assumed that the subjects already had reached their upper limit of performance. However, after that the athletes underwent a simulated 3 w…
Neuromuscular fatigue induced by an isotonic heavy-resistance loading protocol in knee extensors.
2009
Abstract The main aim of this study was to assess neuromuscular fatigue during a typical high-load, low-repetition loading protocol. Muscle stimulations were used to assess maximum voluntary contraction, resting single- and double-pulse twitch characteristics, and superimposed double-pulse twitch force (used to calculate voluntary activation) before and after an acute knee extension loading protocol. In our participants, who had previous resistance training experience, the mean voluntary activation level was 96.2% in an unfatigued state. Maximum voluntary contraction (−11.8%), resting double-pulse twitch force (−10.6%), and voluntary activation (−2.1%) were markedly decreased as a consequen…
Knee and ankle joint stiffness in sprint running.
2002
Stiffness has often been considered as a regulated property of the neuromuscular system. The purpose of this study was to examine the ankle and knee joint stiffness regulation during sprint running.Ten male sprinters ran at the constant relative speeds of 70, 80, 90, and 100% over a force platform, and ground reaction forces, kinematic, and EMG parameters were collected.The results indicated that with increasing running speed the average joint stiffness (change in joint moment divided by change in joint angle) was constant (7 N x m x deg(-1)) in the ankle joint and increased from 17 to 24 N x m x deg(-1) (P0.01) in the knee joint.The observed constant ankle joint stiffness may depend on (co…
Neuromuscular fatigue following constant versus variable-intensity endurance cycling in triathletes
2008
International audience; The aim of this study was to determine whether variable power cycling produced greater neuromuscular fatigue of knee extensor muscles than constant power cycling at the same mean power output. Eight male triathletes (age : 33 ± 5 yr, mass : 74 ± 4 kg, OV&2max : 62 ± 5 ml.kg-1.min-1, maximal aerobic power : 392 ± 17 W) performed two 30 min trials on a cycle ergometer in a random order. Cycling exercise was performed either at a constant power output (CP) corresponding to 75% of the maximal aerobic power (MAP) or a variable power output (VP) with alternating ± 15%, ± 5%, and ± 10% of 75% MAP approximately every 5 min. Maximal voluntary contraction (MVC) torque, maximal…
Neural activation after maximal isometric contractions at different muscle lengths.
2006
DESBROSSES K., N. BABAULT, G. SCAGLIONI, J.-P. MEYER, and M. POUSSON. Neural Activation after Maximal Isometric Contractions at Different Muscle Lengths. Med. Sci. Sports Exerc., Vol. 38, No. 5, pp. 937–944, 2006. Purpose: To investigate i) whether neural activation dependence on muscle length is preserved with neuromuscular fatigue and ii) whether fatigue induced by a maximal isometric exercise is muscle length dependent. Methods: Twelve male subjects performed two fatiguing quadriceps muscle exercises: FS is the fatigue carried out at short muscle length (S) (S = 40- of knee flexion) and FL is the fatigue at long muscle length (L) (L = 100-). Before and after each fatiguing exercise (i.e.…
Leg stiffness modulation during exhaustive stretch-shortening cycle exercise.
2007
The present study examined the effects of muscle activity modulation on leg stiffness during an exhaustive stretch-shortening cycle (SSC) exercise in eight male subjects. Reaction force, electromyography (EMG) of the soleus (Sol), gastrocnemius (Ga) and vastus lateralis (VL) muscles and sledge seat position were recorded during the SSC exercise, consisting of 100 maximal intermittent drop jumps followed by a continuous submaximal jumping until exhaustion, on a sledge apparatus. Metabolic loading was determined by measuring blood lactate (La). No change was found in leg stiffness during the maximal jumps, whereas the subsequent submaximal jumping induced a significant reduction by 27+/-12% (…
Effects of plantar flexor muscle fatigue induced by electromyostimulation on postural coordination
2007
International audience; The aim of the present study was to investigate the influence of a modification of an intrinsic capacity (plantar flexor strength) on the implementation of in-phase and anti-phase mode of coordination. Analysis of hip and ankle relative phases during fore-aft tracking task was done before and after an electromyostimulation fatigue protocol on the soleus muscles. Results showed participants used exclusively in-phase and anti-phase modes of coordination, with a sudden switch from one to the other with target frequency increase. Regarding tracking tasks, fatigue induces a decrease of performance for lower frequencies, and a significant decrease of switch frequency (−0.0…