Muscular Endurance In Sports

Muscle fiber distribution

The proportions of type I and type II muscle fibers have a strong effect on how your body performs over long distance activities. An average person has roughly the same amount of both muscle fiber types, although some elite athletes may have up to 70-80% of a specific fiber type. This is significant because they both have different metabolic properties and responses to training. Generally speaking, slow-twitch fibers (type I) are more suited for prolonged exercises where prolonged contraction and energy efficiency are of the essence. Fast-twitch fibers (type IIa & type IIb) are more suited for activities that require stronger force production. Type I fibers are also smaller in size and contain a higher number of mitochondria (powerhouse of the cell) and myoglobin (an iron and oxygen-binding protein found in the cardiac and skeletal muscle tissue). These further increases their ability to resist fatigue.

Energy sources

The main sources of fuel in the body are glucose, stored muscle glycogen, and free fatty acids. The availability of these energy substrates and how the muscles use them can have an enormous impact on muscular endurance. Because muscles have limited amounts of stored energy, they must use metabolic pathways like substrate-level phosphorylation (aerobic and anaerobic) and oxidative phosphorylation (aerobic) to produce adenosine triphosphate (ATP). The latter relies on sufficient oxygen delivery to contracting muscles. This allows you to oxidize glucose and fat for fuel.

Technique and movement efficiency

Technique and movement efficiency also have a significant impact on muscular endurance. More specifically, how many motor units (a motor neuron and all the muscle fibers it innervates) are activated during exercise, as well as how efficiently they are recruited via the central nervous system (see: rate coding & motor unit synchronization). 

During prolonged intense exercises, the accumulation of blood lactate also hinders cross-bridge formation and the excitation-contraction coupling. These disturb the muscle’s mechanical properties, which results in a decrease in overall performance (lower force production, peak force and velocity). This makes movement economy a crucial component in your athletic performance.

Technique is also highly sport-specific. For example, long-distance runners must have an optimal stride cadence (the number of strides taken per second) and stride length (the distance traveled on each stride) for the best performance. Placing your foot under your center of gravity while maintaining as long of a stride as possible also prevents potential adverse effects such as understriding and overstriding. These factors maximize flight time while reducing ground contact time and friction (ground force efficiency). All of which are essential for running mechanics and movement economy.

Of course, similar technique-related performance factors can be found in other sports as well (e.g. swimming and stroke cadence, speed skating and glide/push cadence, etc.).

Age and gender

In addition to the physiological and technical factors mentioned above, your age and gender also have a significant impact on local muscle endurance.

On average, maximal oxygen uptake declines ~5-10% per decade after the age of 30 depending on your physical activivity. This leads to a lower cardiac output (amount of blood the heart pumps) as well as reduced maximum heart rate while exercising. Studies have also shown that muscular strength declines at a rate of ~3-5% every decade after the age of 30. This is due to an age-related loss in muscle mass, known as sarcopenia. This is a result of reduced muscle fiber size (atrophy) and number (hypoplasia), which contribute to increased obesity, reduced quality of life, osteoporosis, and metabolic health. Interestingly, this slow degeneration mostly affects fast-twitch muscle fibers, whereas slow-twitch fibers maintain their functionality relatively well with age.

Gender is another factor that has a strong impact on muscular endurance. Males have a naturally higher maximal oxygen uptake (VO₂max) than women. This is due to having larger hearts, more muscle mass, higher levels of hemoglobin and less body fat. As a result, men have consistently outperformed their female counterparts in various sports by approximately 10-12% depending on the event. However, women usually have proportionally more fatigue-resistant type I muscle fibers than men. Some studies have also hinted that females may be able to burn fat for fuel more efficiently. This may be a result of estrogen’s (female sex hormone) effect on the metabolism.