The Effects of Static Stretching on Performance

Recent research suggests that pre-event stretching may hinder, rather than improve, athletic performance. Martyn Jones explains

Traditionally athletes' pre-training and competition warm up has followed the same protocol - aerobic exercise to raise body temperature, some static stretching followed by drills specific to their event. But recent research has cast a doubt over the use of static stretching.

A study by Young and Elliott (2001) examined the effects of four different warm up protocols upon the performance of drop (depth) jumps. The participants were active and from a variety of sports, including athletics, all completed the test (on different days) after undertaking each of the warm up protocols. They completed a five minute jog, and one of the following warm ups:

• Static stretching of the calf, gluteals and quadriceps muscles.
• Proprioceptive Neuromuscular Facilitation (PNF) stretching of the same muscles.
• Maximum isometric contraction (MVC) of the same muscles.
• No stretching at all.

They then undertook a four minute slow walk before being tested on three drop jumps. The drop jump test is particularly specific to all runners and jumpers as it is a method of testing the stretch-shortening cycle (SSC). A SSC is a particular type of muscle action that involves a rapid eccentric (lengthening) contraction of the muscles followed by a concentric (shortening) contraction, running is such a movement. In running and jumping the eccentric phase is the landing phase and the concentric phase is the push off. The power produced in such a movement is aided by the utilisation of energy stored in the elastic tissue surrounding the muscles and the tendon. The elastic tissue is stretched during the eccentric phase, energy is stored as a result and is subsequently released during the concentric phase - the body's soft tissue basically acts as an elastic band. SSC strength is fairly independent of an athlete concentric strength level, and requires specific training methods to enhance it e.g plyometrics and resisted/assisted running.

STUDY RESULTS
The study revealed that the warm up protocol of jogging only resulted in the best performance in the drop jump. While the worse was the warm up involving static stretching, which had a decrease in performance of 7% compared to the no stretching warm up. The warm up protocols, PNF stretching (3.2%) and MVC (1.1%) also resulted in decreased performance.

Other studies have reported similar decreases in performance after static stretching, Nelson et al showed a 4% and Knudson et al reported an average decrease of 3%, with the majority having a 7.5% decrease, both studies tested a countermovement squat jump (a SSC movement). Similar levels of decreased performance have been reported during strength tests.

The cause of this decreased performance is not fully understood. One reason may be related to musclo-tendinous stiffness. Before any landing (i.e. ground contact in running) the muscles and tendons of the leg are pre-activated in anticipation of the landing forces. This pre activation limits the amount of lengthening of the muscle fibers (i.e. increases stiffness). Increased stiffness is important to performance for two inter-related reasons. Firstly, it results in less flexion (give) of the ankle, knee and hip joints upon landing, meaning any ground contact will be shorter, which in turn means cadence will be faster. It should be remembered that the first part of the ground contact acts as a braking phase, so there will also be less decrease in horizontal velocity. Secondly, the shorter ground contact time also means a faster conversion between eccentric and concentric muscle actions which results in more power being produced during the concentric phase. So the second part of ground contact, the propulsion phase, will be more powerful, and therefore increase stride length. Stretching seems to decrease the amount of stiffness in the stretched muscles.

FURTHER RESEARCH
The decrease in performance has been shown to last for at least one hour, but the decrease reduces over time (Fowles et al). It has been recommended that any stretching should take place two hours before exercises (Balyi).

There are still some unanswered questions arising from these research studies. The reported decrease in performance would result in an 11.0sec 100m sprinter running 11.8sec, which from personal experience is not the case.

Most athletes use running drills after stretching, which may well have an effect on the level of stiffness. There may be an increase in stiffness, towards normal levels, caused by these ground contacts. Much more research is needed into determining optimal warm up protocols -there may even be a protocol for the temporary increase in stiffness levels. Coaches could carry out their own research in this area using different warm up protocols and using exercises such as hop and bounds as the test.

To avoid any potential adverse effects of stretching and also to decrease the risk of injury a functional warm up should be used. This involves a general warm up followed by exercise similar in nature to the performance. This will result in the specific soft tissue used in the performance being warmed and worked in a similar range of motion to that used in the subsequent performance. These exercises should commence with low intensity and limited range of motion, and increasing in speed and range of motion throughout the warm up.

As someone who spent 20 minutes before every training session stretching, and who now advises Athletes not to stretch, implementing the above recommendations may be difficult. But all the available scientific evidence points to restricting its use to after training, or well before training.

REFERENCES
Balyi, I. (2002). Paradigm shifts in coaching. Faster, Higher, Stronger, Sports Coach UK, April, 24-26.

Fowles, J.R., Sale, D.G. & MacDougall, J. D. (2000). Reduced strength after passive stretch of the human plantorflexors. Journal of Applied Physiology, 89, 1179-1188.

Knudson, D., Bennett+ K., Corn, R., Leick, D., & Smith, C. (2001). Acute effects of stretching are not evident in the kinematics of the vertical jump. Journal of Strength and Conditioning, 15(1), 98-1 01.

Nelson, A., Cornwell, A., & Heise, G.D. (1996). Acute stretching exercises and vertical jump stored elastic energy. Medicine and Science in Sport and Exercise, 28, 5156.

Young, W., & Elliott, S. (2001). Acute effects of static stretching, PNF stretching, and MVC contractions on explosive force production. Research Quarterly for Exercise and Sport, 72(3), 273-279.

Martyn Jones has an MSc in Science of Sport Coaching and has recently started the supervised experience programme of the British Association of Sport and Exercise Sciences in Sport Biomechanics. He coaches athletes from Sheffield University, and is partly through a UKA Level 4 coaching qualification in sprints.

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