Static Stretching Reduces Muscle Strength and Force
Active stretching, dynamic stretching - there is always a debate about stretching. A study recently conducted in Brazil investigated the influence that active stretching had on maximal isometric muscle strength and rate of force development. This was determined using time intervals of 30, 50, 100, and 200 milliseconds relative to the onset of muscle contraction. It has been proposed that along with increasing the range of motion, stretching may also improve performance and reduce injuries. On the other hand, some studies have shown that maximal voluntary contraction, torque, and jump height are negatively affected by stretching.1
The fifteen men participating in the study were physical education students involved in recreational sports (soccer, basketball, volleyball). Each subject had not participated in regular strength training for at least six months before the start of the study. Each subject performed three separate sessions that were separated by 3-5 days. The first session involved 5 maximal isometric contractions for knee extensors in the isokinetic dynamometer. The next two sessions the subjects randomly performed two maximal isometric contractions for the knee extensors in the isokinetic dynamometer to determine the maximal voluntary contraction (MVC) and the rate of force development (RFD), and two active static stretching exercises for the dominant leg extensors (10x30 seconds for each exercise with 20-second rest intervals between sets). Immediately after stretching (approximately three minutes), the isokinetic test was repeated. The RFD was calculated using the average slope of the moment-time curve at time intervals of 0-30, 0-50, 0-100, 0-150, and 0-200 milliseconds relative to the onset of muscle contraction.2
The results of the study revealed that the MVC was reduced after stretching. The RFD at intervals 0-30, 0-50, and 0-100 milliseconds did not change after stretching. However, the RFD measured at intervals of 0-150 and 0-200 was significantly lower after stretching. Consequently, it can be concluded that explosive muscular actions of a very short duration seem less affected by active static stretching when compared with actions using maximal muscle strength.3
The results of this research were very similar to that in other studies. Prior studies have shown that acute static stretching impairs muscle force and torque. In this particular study, the MVC was reduced by 5%, which is consistent with previous research. This was the first research known to be conducted that analyzed the effects of stretching on their RFD measured at different time intervals from the onset of contraction. This was also reduced by about 5-7% in this particular study, and similar to maximal strength, the lower RFD after stretching may also be explained by the reduction of muscle-tendon stiffness. Data from this research may help explain the different effects that stretching has on explosive movements.4
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