The vertical leap is an essential aspect of many sports, including basketball for grabbing rebounds, volleyball for spiking the ball and soccer for heading the ball. Improving vertical leap is a priority for many athletes competing in these sports. And while stretching the hamstrings, quadriceps, calves and other muscle groups in the legs can help you prevent injuries while training for the vertical leap, stretching cannot directly help increase your vertical leap.
Background
The amount of height you are able to achieve with a vertical leap depends on the amount of force the muscle fibers in your legs are able to generate. According to Marshall University, the muscle fibers create this force using the stretch-shortening cycle, which is the body's natural response to rapid muscle movements. When you bend your knees and explode upward to complete a vertical leap, the body forces the muscles to contract eccentrically and stiffen, resisting the downward motion and then reversing it.
Elastic Energy
Elastic energy refers to the amount of potential energy, or pent-up stress, that an elastic object, like a muscle, has in a flexed state. The stretch-shortening cycle, which drives the vertical leap, relies on the elastic energy of the leg muscles to generate upward force. Unfortunately, as Georgia Southern University notes, performing stretching exercises has no significant impact on the amount of elastic energy your leg muscles can store and ultimately expend.
Research
A 2000 study published in the "Journal of Biomechanics" showed that decreasing the stiffness and reflex of a muscle group through stretching decreased the amount of force that muscle group was able to produce -- force that is essential for powering the mechanics of a vertical leap. The study utilized EMG, or electromyography, readings to monitor the activity of muscle fibers during exercise.
Opposite Implications
Beyond not being able aid in increasing your vertical leap, stretching your legs may actually have a negative impact on your leap height. A 2001 study published in the "Journal of Strength and Conditioning Research" showed that subjects who used proprioceptive muscular facilitation, or PNF, flexibility stretching exercises prior to performing a vertical leap had poorer performances in comparison to when they performed nonstretching exercises.
Stretching Vs. Warming
According to Georgia Southern University, warming the muscles with isometric contractions is a better strategy for preparing the body for a vertical leap than stretching. Isometric contractions, also known as static contractions, involve putting stress on muscles without causing the fibers to lengthen or shorten. An example is performing wall squats, wherein you place your back against a wall and bend you knees until your thighs are parallel to the floor. You then hold your body against the wall for as long as you can with your quadriceps and the other muscle groups in your legs.
References
- Marshall University: The Effects of Static Stretching on Vertical Jump Performance
- Georgia Southern University: Effects of Dynamic, Static Stretch...
- "Journal of Biomechanics": Stretch-shortening cycle: a powerful model to study normal and fatigued muscle
- "Journal of Strength and Conditioning Research": Effect of Warm-Up and Flexibility Treatments on Vertical Jump Performance
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