Many sports require an athlete to be explosive and powerful. Athletes are required to accelerate and decelerate rapidly, change direction quickly and efficiently, jump maximally, swing or throw as hard as possible, and maintain this maximal performance for an extended period. Strength, power, and work capacity are key variables that can influence an athlete’s ability to perform all of these tasks.
Strength, Power, and Hypertrophy
Muscle strength can be defined as the maximal amount of force that a muscle or muscle group can generate. It is not to be confused with muscle power, which is a product of both force and the speed or velocity at which force can be generated. A common misconception is an idea that the strongest athlete will be the fastest or most explosive. While this is not the case, it is true that a physically stronger athlete will be a faster and more explosive athlete. Therefore, developing strength is an essential performance variable. Many athletes engage in structured weight-training programs in the off-season that target maximizing strength before the competitive season begins. Power is the ability to generate a large amount of force quickly. As the speed of movement increases, the amount of force that the muscle is capable of producing decreases. As the speed of movement slows, the muscle is capable of producing more force, and maximal force is produced at slower speeds. This is the disconnect between strength, or maximal force, and power. A sprinter has only 0.15-0.18 seconds to apply as much force as possible to the ground while running. If the muscle isn’t well trained to apply force as quickly as possible, it will be difficult for training to carry over into the event. Strength and power are developed through physiological and neurological changes to the muscle. Physiologically, through training, the entire muscle can increase in size, including the cross-sectional area of the muscle and the density of muscle fibers within. A larger, denser muscle results in an improvement in strength and power. These changes are largely influenced by the endocrine system. During exercise, a cascade of hormonal events takes place. Amounts of stress and catabolic hormones—those that induce the breakdown of larger molecules into smaller ones (cortisol, epinephrine, and norepinephrine)—increase to meet the demands of the training event. Cortisol, epinephrine, and norepinephrine act catabolically to break down carbohydrates, fat, and protein stores; they also act on the nervous system to increase motor unit and muscle fiber recruitment. A motor unit simply refers to a motor neuron and the muscle fibers it connects. Activation of more motor units, and consequently more muscle fibers, will increase the number of active fibers contributing to the development of muscle contraction and force. The build-up of these catabolic hormones is followed by a response of anabolic hormones, including testosterone, growth hormone, and IGF1 (insulin-like growth factor 1) that act on the muscle to initiate anabolic muscle-building and recovery responses. Anabolic hormones spark increases in the rates of protein synthesis, or muscle building. This process of creating a larger, denser muscle is known as hypertrophy, and these changes elicit improvements in the muscle’s strength and power capabilities. Hypertrophy is a common goal for bodybuilders, who are trying to create the best, biggest, and most aesthetic-looking muscles. The development of sports supplements has been strongly influenced by bodybuilding, and although many sports supplements are targeted toward bodybuilders, they are also used by other athletes hoping to build lean body mass. Another common misconception is that the only way to have stronger and more powerful muscles is for them to get bigger. The majority of changes in strength and power are actually the result of neurological changes. The body is complex and requires many muscle fibers and motor units working together to produce force. Each muscle is made up of thousands of muscle fibers and several motor units. Various muscle fibers are grouped together to make up a motor unit. The speed at which these motor units are activated, the number of muscle fibers innervated within each motor unit, and the synchronization of motor units within the same muscle and other muscles working together all affect muscle performance.
Some of the neurological changes that take place through training include the following:
- An increase in the number of muscle fibers that contract simultaneously. Based on neurological signals, your brain recruits and activates more muscle fibers to contract. By applying resistance and requiring the muscle to develop more force, the body will adapt neurologically and signal more muscle fibers to contract.
- Increase in the rate of contraction of muscle fibers. The faster the muscle is able to contract and develop force, the more power it will produce.
- Improved efficiency and synchronization of firing muscle fibers. Through adaptation to training, the muscle fibers become more efficient and operate in sync.
- Decreased inhibition of antagonistic muscle fibers. During a leg extension where the quadriceps are the primary moving muscle, the hamstrings contract and inhibit leg extension. Training lessens this degree of inhibition.
- Improved efficiency of stretch reflexes controlling muscle tension. You’ve probably heard the analogy that your muscles are like a rubber band: The farther they are stretched, the faster and more forcefully they contract in the opposite direction. This stretch reflex can be trained, improving its efficiency and the amount of force and speed at which muscle fibers contract.
- Improved conduction velocity and excitation threshold of nerve fibers. This involves the speed at which neural signals activate motor units and the number of muscle fibers activated with each signal.