Principle of Muscle Balance

Resistance-training programs should be designed to promote strength development in all of the major muscle groups. Emphasizing certain muscle groups can produce muscle imbalance, which may in time lead to muscle injury. This is because whenever a muscle group is disproportionately stronger than its antagonist, the antagonist is predisposed to injury.

The important point is that muscle groups should not be trained in isolation. If the muscles on one side of a joint are worked, then the opposing muscles should likewise be worked, even though the workloads may not be identical. The problem of maintaining desirable muscle balance can be simplified by training all of the major muscle groups.

For balanced muscle development and to reduce the risk of injury, the source identifies 12 major muscle groups to strengthen: trapezius, deltoids, pectorals, latissimus dorsi, erector spinae, triceps, biceps, abdominals, quadriceps, glutes/hip, calves, and hamstrings. It is also advisable to train the obliques and the adductors/abductors. Training some muscles while excluding others typically produces poorer overall results and may lead to injuries.

The source pairs this principle with a table of specific exercises for the major groups that aren't already covered as antigravity/atrophic-weakening groups (see antigravity-musculature / atrophic-weakening-muscles for those, and strength-conditioning-program for the full 15-group equipment map — this is a complementary exercise set for the same muscles, not a duplicate):

• Develop strength in ALL major muscle groups; do not train muscles in isolation.
• A muscle disproportionately stronger than its antagonist predisposes the antagonist to injury.
• Work both sides of a joint (workloads need not be identical).
• 12 major muscle groups: trapezius, deltoids, pectorals, lats, erector spinae, triceps, biceps, abdominals, quadriceps, glutes/hip, calves, hamstrings (+ obliques and adductors/abductors).
• Source's muscle-balance exercise examples for the non-antigravity groups: pectorals, deltoid, biceps, triceps, hamstrings, rotator cuff (see table above).

• push-pull — push-pull pairing creates balance between agonist and antagonist groups.
• specificity — specificity also calls for training antagonists and stabilizers.
• arrangement-of-exercises — ordering exercises across the major groups supports balance.
• exercise-selection — selecting across the 12 major groups is the program-design application.
• muscle-balance-injury-prevention — imbalance as an injury mechanism.
• body-shape-frame-types — the same "train the underdeveloped side" logic applied to visual/aesthetic symmetry rather than injury prevention.
• resistance-training-safety-guidelines — the "exercise antagonist muscle groups" and "all major muscle groups" guidelines.
• antigravity-musculature / atrophic-weakening-muscles — the other major-group subsets, with their own source exercise tables.
• strength-conditioning-program — the full 15-group exercise/equipment map this table complements.