5.7.1: Strength Is a Good Indicator, Not the Only Indicator

Because muscle size and muscle force output are tightly correlated, strength progression is the most practical tool we have for confirming that growth is occurring. If your squat has risen from 100 kg to 120 kg for the same rep range and ROM over a year, your quadriceps are almost certainly larger. But strength is not a pure measure of hypertrophy. Several adaptations can increase force output with zero additional contractile tissue:

• Neurological adaptations: The nervous system becomes more efficient at recruiting high‑threshold motor units, increasing rate coding (the speed at which motor neurons fire repeated signals to their fibers), and reducing antagonist co‑contraction. These changes alone can account for significant strength gains, particularly in the first few months of training, without any measurable hypertrophy.
• Tendon stiffness: Resistance training increases the stiffness of the muscle‑tendon unit. A stiffer tendon transmits force from muscle to bone more efficiently and with less energy loss, meaning the same contractile force results in a larger external lift.
• Lateral force transmission: Muscle fibers do not only transmit force longitudinally, from sarcomere to sarcomere. They also transmit force laterally, across the cell membrane and through the surrounding connective tissue matrix (the endomysium, perimysium, and epimysium). Chris Beardsley has highlighted that the extracellular matrix adapts to training by becoming stiffer and more organized, improving lateral force transmission pathways. This structural remodeling can increase whole‑muscle force output independently of myofibrillar hypertrophy [17].
• Technique and coordination: Simply becoming more skilled at a lift—finding better leverages, grooving the bar path, synchronizing muscle groups—increases the weight you can move without any change in muscle size.

Strength is not a useless metric; it is a necessary condition for long‑term hypertrophy (you cannot add contractile protein over months and not get stronger), but it is not a sufficient condition in the short term (a strength increase this week might be neural, not contractile). Over a training lifetime, strength is the most reliable proxy you have, but you should not panic if a mesocycle produces visible size change with only modest strength improvement, and you should not assume that a max‑out PR automatically means you are in a growth phase.