Physical fitness consists of three key components, sometimes referred to as the three S's: strength, stamina and suppleness. Stamina is also known as endurance, and suppleness is synonymous with flexibility. Suppleness is perhaps the easiest for the layman to define: the ability to bend or stretch without damage. The difference between strength and stamina, however, may be less intuitive. Both terms embody the larger concept of how much work a given muscle can do.
Definitions
In "Muskulosekeletal Interventions," a chapter on muscular strength and endurance by Prof. William Prentice defines strength as "the ability of a muscle to generate force against some resistance," while endurance is "the ability to perform repetitive muscular contractions against some resistance for an extended period of time." According to Prentice, the two concepts are closely related, and increases in muscle strength typically go hand-in-hand with increases in endurance.
Sources
Strength and endurance correlate to the number of fast-twitch and slow-twitch muscle fibers in a given muscle. (For this reason, strength and endurance are measured for individual muscles, not the whole body. In "Human Biology," Daniel Chiras describes endurance as associated with slow-twitch fibers while strength correlates with more fast-twitch fibers. Chiras cites the example of back muscles, which exert force over several hours to maintain posture and which are rich in slow-twitch fibers. Fast-twitch fibers are more numerous, for example, in the arm.
Cardiovascular Endurance
The term "endurance" is also used to refer specifically to cardiovascular endurance. This sense of endurance is synonymous with stamina. As defined by Peter Givens and Michael Reiss in "Human Biology and Health Studies," stamina is "the ability to keep going without gasping for breath." Exercises that build muscle endurance also improve cardiovascular function. For example, Chiras states that aerobic exercise strengthens heart muscle, tones muscles involved in breathing and increases blood volume, all of which optimize oxygen supply for exercising muscles, increasing stamina.
Building Strength and Stamina
According to Prof. Prentice, increasing muscle strength requires resistance training that overloads the muscle: "For a muscle to improve in strength, it must be forced to work at a higher level than it is accustomed to." Increasing endurance, on the other hand, relies on working muscles for a longer period of time, but with less intensity. In "Fitness and Health," authors Brian Sharkey and Steven Gaskill state: "When you have sufficient strength for the task, gains in endurance come with relative ease."
Balancing Strength and Endurance
Sharkey and Gaskill also warn that "excessive attention to strength" can actually decrease sports performance. Once you have adequate strength, turn your focus to developing increased muscular endurance. According to Sharkey and Gaskill, adequate strength roughly equates to the ability to do a given action 10 times, such as executing 10 tennis shots or navigating 10 downhill ski turns. Prentice also emphasizes the importance of endurance in rehabilitative settings since endurance is more central for carrying out activities of everyday living.
References
- "Musculoskeletal Interventions: Techniques for Therapeutic Exercise"; Chapter 8--Impaired Muscle Performance: Regaining Muscular Strength and Endurance; William Prentice; 2006
- "Human Biology"; Daniel Chiras; 2005
- "Human Biology and Health Studies"; Peter Givens and Michael Reiss; 2002
- "Fitness and Health"; Brian J. Sharkey and Steven E. Gaskill; 2007
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