Power In Sports And Athletic Performance - And Why You Need It

The stretch-shortening cycle

Stretch-shortening cycle (SSC) refers to a muscle action where an active muscle stretch is immediately followed by an active muscle shortening. Thus, producing far more force than a regular contraction (e.g. a countermovement jump versus a squat jump). The stretch-shortening cycle consists of three phases; the eccentric phase, the amortization phase, and the concentric phase.

• Eccentric phase: The muscle lengthening phase of a movement (the pre-stretch phase).
• Amortization phase: The transition period between eccentric and concentric contraction, where the tendon is loaded (the ”time to rebound” phase).
• Concentric phase: Releasing the stored energy by contracting the muscles lengthened in the eccentric phase.

Although this phenomenon is well documented in scientific literature, its exact mechanisms are still under debate. One theory behind it is that muscles and tendons are able to store elastic energy in the pre-stretch phase of the movement, which is then released when the muscle is shortened. The more force is applied to the tendon, the more force it generates as it returns to its normal length (rate of loading). In a way, this makes your muscles and tendons act like a rubber band and generate more force than the relative strength of the muscle.

If you are interested to read more about the stretch-shortening cycle, you can find a more in-depth article here.

Factors that affect power in sports

In addition to the stretch-shortening cycle, there are several other factors that affect your rate of force development. These factors include: 

• Age
• Sex
• Genetics
• Maximal strength
• Muscle recruitment
• Fatigue
• Training background
• Technique
• Joint angle
• Muscle temperature

Below you can find a more detailed description of each, as well as how they affect your capability to produce power.

Age, genetics & sex

Genetics refers to the biological traits that you have inherited from your biological parents. This includes factors such as height, weight and muscle mass. However, perhaps the most important factor is muscle fiber distribution. Fast-twitch muscle fibers (type I) tend to fire quicker and with more force than slow-twitch muscle fibers. Thus, making them better suited for activities that require strength and explosiveness. Furthermore, the firing frequency (rate coding), motor unit synchronization (the near simultaneous discharge of action potentials by motor units) and coordination also have a significant impact on force production.

Age has a significant effect on force production. The general consensus is that the muscles of older individuals contract with less force, have slower relaxation rates, and show a downward shift in their force-velocity relationship. The main reason for this is an age-related loss of muscle mass called sarcopenia. This loss is greatest in type II fibers which affects total strength as well as the speed of movement. Additionally, studies have also indicated that the ability to rapidly recruit motor units decreases with age.

How to increase power through training?

According to the American College of Sports Medicine (2009), progression in power training can be divided into two strategies; 1) strength training and 2) using light loads (0-60% of 1 RM for lower body exercises; 30-60% of 1 RM for upper body exercises) performed at a fast contraction velocity and each exercise should be repeated for 3-5 times. Thus, power training focuses on improving its two main components; speed and strength. The main difference between power specific exercises and strength training is accelerating the load throughout the entire range of motion of a specific movement.

In practice this means performing explosive exercises with relatively high resistance (50-90% of one-repetition maximum) and fewer repetitions (1-5) per set. Once comfortable with a specific movement, the same exercises can be performed with lighter loads to increase the velocity of the movement. Power training also requires longer recovery periods between sets (up to 5mins), and sometimes even between repetitions. This ensures that the training focuses on rapidly recruiting fast motor units instead of tiring the muscles with multiple repetitions. Thus, allowing athletes to be more explosive without added muscle mass.

Power can be trained in two different ways; cyclically (continuously) and acyclically (one repetition at a time). Acyclical exercises utilize slightly heavier loads and are often used in sports that require a single explosive movement (e.g. shot put, javelin throw, high jump, etc.). On the other hand, continuous (cyclical) exercises improve performance in sports that rely on short (<10s) intense bursts (e.g. sprinting, speed skating, etc.). However, these methods can always be varied according to personal needs. For example, acyclical lifts are still useful for sprinters because they improve the maximal power output of the muscles, regardless of the fact that the competition distance requires powerful consecutive strides.

Although these explosive high-intensity/low repetition exercises (e.g. powerlifting) form the foundation of power training, there are a few distinct training styles that are used most commonly. These include plyometric training (explosive jumps, leaps etc.), ballistic training (explosive throws), and contrast training (exercises with alternating weights). To learn more, take a look at our in-depth power training post.

The benefits of power in sports

Power offers several benefits in a sports setting. These include higher maximal speed, faster acceleration, and better agility. Interestingly, increases in power capability have also shown improvements in endurance performance. The reason for this is that power training can shorten the normal ground contact time (0,15-0,25s) of each step, providing more efficiency for long-distance activities.

However, the positives do not end there. Here is a full chart of the benefits of power in sports;