Principle of Individuality (Individual Differences)

A person's genetics determine, to a great extent, how quickly and to what degree his or her body adapts to an exercise program. The person's initial fitness level also contributes to the variation in training response. Other factors — growth rates, metabolism, and the ability to tolerate exercise stress — likewise lead to different rates of training results.

This principle governs how training systems should be applied: one system of training will not work optimally for all individuals and muscle groups. Programs should be appropriate to the individual; systems used by a competitive bodybuilder or weight lifter are not likely to be tolerated by a beginner who lacks the fitness level or training experience. A training log is invaluable for determining which programs or systems work best for a given individual — including which system works best and how long until a plateau develops.

Body type connects here: expert guidance on diet and intensive exercise can help an athlete partially modify their somatotype (body-shape-somatotypes — endomorph/mesomorph/ectomorph) within the limits of their genetic make-up, but any body type can be developed by proper resistance training and nutrition (Bloomfield et al., 1992).

• Genetics largely determine the rate and degree of adaptation.
• Initial fitness level also drives variation in response.
• Other factors: growth rate, metabolism, tolerance of exercise stress.
• No single system is optimal for all individuals or muscle groups.
• Programs must match the individual's fitness level and experience; a training log helps identify what works.

• systems-overview — system choice must be matched to the individual's level.
• progression — the rate of progression depends on individual response.
• specificity — individual goals shape which specific adaptations are sought.
• combo-program — the four sample-program tiers (basic/athletic/bodybuilding/combo) reflect individual differences.
• muscle-fiber-types — fiber distribution is genetically fixed, a source of individual variation.
• body-shape-somatotypes — the somatotype system this module's body-type note refers to.