No abstract

Although several studies have investigated the acute effect of static stretching exercises, the duration of exercises that negatively affects performance has not been ascertained. This study was conducted to determine the acute effect of different static stretching durations on quadriceps isometric and isokinetic peak torque production. The 50 participants were randomly allocated into five equivalent sized groups and were asked to perform a stretching exercise of different duration (no stretch, 10-second stretch, 20-second stretch, 30-second stretch, and 60-second stretch). The knee flexion range of motion and the isometric and concentric isokinetic peak torques of the quadriceps were measured before and after a static stretching exercise in the four experimental groups. The same parameters were examined in the control group (no stretch) without stretching, before and after a 5-minute passive rest. There were no significant differences among groups before the experimentation regarding their physical characteristics and performances (P > 0.05). These results reflect the different groups' homogeneity. Significant knee joint flexibility increases (P < 0.001) and significant isometric and isokinetic peak torque reductions (P < 0.05-0.001) have been shown to occur only after 30 and 60 seconds of quadriceps static stretching. Stretching reduced isometric peak torque by 8.5% and 16.0%, respectively. Concerning isokinetic peak torque after 30 and 60 seconds of stretching, it was reduced by 5.5% vs. 11.6% at 60 degrees/s and by 5.8% vs. 10.0% at 180 degrees/s. We suggest that torque decrements are related to changes of muscle neuromechanical properties. It is recommended that static stretching exercises of a muscle group for more than 30 seconds of duration be avoided before performances requiring maximal strength.

Objectives: To compare the effects of proprioceptive neuromuscular facilitation (PNF) and isokinetic training on fibre type distribution and cross sectional area of the vastus lateralis muscle. Methods: Twenty four male university students were divided into two equal groups: PNF training and isokinetic training (ISO). The training regimen for the PNF group consisted of three sets of 30 repetitions against maximal resistance, alternating two patterns of sequential movements of the right lower extremity: (a) toe flexion and ankle plantar flexion and eversion; (b) knee extension and hip extension, abduction, and internal rotation. The ISO group performed three sets of 30 repetitions alternating knee extension and flexion of the right leg at angular velocities of 180 and 90˚/s in an isokinetic dynamometer (Cybex). Both groups trained three times a week for a total of eight weeks. Muscle biopsy specimens were obtained from the right vastus lateralis muscle before and after training. 1 This means that PNF exercises are very similar to the actions and movements found in various sports. They therefore appear to be more suitable for performance enhancement than conventional weight training programmes. PNF is therefore often used as an alternative form of progressive resistive exercise by physiotherapists as its use should be more advantageous than the usual strength programmes in athletic injury rehabilitation.2 Nelson et al 3 compared the effects of PNF and weight training. They reported similar strength gains, but PNF was better at enhancing performance, as evidenced by the larger gains in throwing distance and jumping height.The use of isokinetic exercise in rehabilitation, conditioning, and research has become widespread since the development of modern isokinetic dynamometers, which provide data on the mechanical properties of muscle under conditions of constant velocity in vivo.Cross sectional studies, using histochemical methods on skeletal muscle from various groups of elite athletes, suggest that the pattern of physical activity affects muscle fibre type predominance. 5More recent longitudinal studies have shown changes in the histochemical fibre type profile after a period of increased physical activity. The effects of PNF training on skeletal muscle fibre composition are not known. Based on the evidence that the pattern of physical activity affects muscle fibre type predominance, we hypothesised that PNF, like isokinetic training, would affect vastus lateralis muscle fibre type predominance and mean area, and that these changes would appear in the type II fibre subgroup. METHODS SubjectsTwenty four male university students were informed of the test procedure, purpose, and known risks before giving their informed consent to participate. The subjects were divided into two equal groups: (a) PNF training (mean (SEM) age 22.2 (1.3) years, height 178.2 (5.3) cm, weight 74.5 (9.2) kg); (b) isokinetic training (ISO; age 20.5 (1.7) years, height 178.9 (6.7) cm, weight 73.3 (9.5) kg). PNF trainingThe training regimen fo...

No abstract

The purpose of this study was to investigate the long-term effects of high intensity resistance training on myosin heavy chain (MHC) isoform composition of single fibres. Muscle biopsies were obtained from the right vastus lateralis of eight bodybuilders (BB) and seven physical education students (PES). Histochemical analyses were used to determine the fibre type distribution and the fibre cross-sectional area. MHC isoform composition of single fibres was determined with protein electrophoresis. The percentage of fibres expressing MHC IIA and MHC I/IIA was larger in BB (P < 0.05), while MHC IIX was completely absent (P < 0.05). In contrast, myofibrilar ATPase histochemistry only revealed a significantly lower percentage of type IIX fibres in BB (P < 0.05). The muscle fibre profile in the vastus lateralis muscle of BB may represent an adaptation based on the mechanical and biochemical demands of the long-term resistance training.