There is an appropriate time and place for both static and dynamic stretching. Appropriate biomechanical position as well as duration of static stretch will determine the yield of benefit. Static stretches should be performed at the end of a work out to bring muscle filaments and sarcomeres to an elongated state. Dynamic warm-up exercises should be used in the beginning of a work out to prepare neuromuscular recruitment. The ideal time to hold a static stretch is 20 to 30 seconds. Any more than that won’t yield much benefit. While individual instructors might not want to use that time to stretch at the end of class, static stretching should not be discouraged in fact it should be encouraged for participants to do after any work out. Whether or not a coach has the appropriate biomechanical and anatomical knowledge to lead and assist a person in static stretching is another question.
Let’s talk microscopically. Every time you work out if at the end of your work out you don’t stretch, on a microscopic level your muscle filaments will heal at a very slightly shortened state. Overtime, if you do not stretch after you work out you’ll begin to lose your range of motion. If you lose your range of motion in particular the Hips or Shoulders it becomes challenging to appropriately recruit the muscles during specific movements.
You will begin to run into overuse injuries in smaller secondary muscle groups because primary muscle groups cannot appropriately be recruited, while simultaneously placing under stress on skeletal joints and soft connective tissue.
On the other hand, if you do static stretch after you work out on a microscopic level your muscles will heal at a slightly elongated state. Therefore you will be able to maintain and potentially increase your range of motion while building muscular strength, power, endurance etc.
This will minimize things like lower back pain, and will ensure you are still able to recruit the appropriate muscles for particular exercises and focus on balanced strength ratios, which in turn will decrease your risk for injury.
If you’re curious about understanding how your body adapts to particular exercise regimens over time, consider reading my book.
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“The Ultimate Heart Rate Training Guide”