Base of support

Base of support is the region of ground the body contacts.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 376.} Balance is the ability to keep the body’s center of gravity over that base.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 376.} The International Personal Trainer Academy (IPTA) defines the limit of stability as the maximum distance the body can move while staying balanced before the base has to change.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 376.}

A person is balanced when their center of gravity falls inside a base suited to the activity; a larger base generally improves balance.^{2International Sports Sciences Association, Strength and Conditioning, p. 143.} Volleyball players passing a ball and shortstops fielding a grounder use wide stances.^{2International Sports Sciences Association, Strength and Conditioning, p. 143.} A lower center of gravity also helps: a football center is more stable with a knuckle on the ground than when standing upright.^{2International Sports Sciences Association, Strength and Conditioning, p. 143.}

In practice

• In standing lifts, the feet form the base, with body weight and load spread evenly over the heel and the first and fifth metatarsal heads, according to ISSA.^{3International Sports Sciences Association, Bodybuilding: The Complete Guide to Unlocking Muscle Hypertrophy, 1st ed., p. 310.}
• In a squat, the combined center of mass of bar and client must stay over the base formed by the feet.^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 78.} A bar lower on the back forces more forward lean, while a front squat keeps the client more upright.^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 78.}
• Excessive forward lean in a squat puts the load in front of the feet; moving the load outside the base sharply increases the chance of losing balance.^{5International Sports Sciences Association, Strength and Conditioning, p. 349.}
• Progress balance work by shrinking the base: two-legged stance, narrower stance, heel-to-toe, then single-leg work.^{6International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 383.} Add unstable surfaces after that progression.^{6International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 383.}