Low-Load Resistance Training Performed to Muscle Failure or Near Muscle Failure Does Not Promote Additional Gains on Muscle Strength, Hypertrophy, and Functional Performance of Older Adults

Lifting weights until you can't lift anymore makes muscles grow bigger no matter how heavy the weights are, but using heavier weights builds more strength than lighter ones.

When performing low-weight resistance exercises, stopping just before complete muscle fatigue results in the same muscle growth as pushing until complete exhaustion.

In frail older adults and trained individuals, lifting weights until muscle failure produces the same increases in leg strength and muscle size whether using heavy or light loads, and taking protein supplements improves strength gains only if the person's usual protein intake is less than 0.8 grams per kilogram of body weight per day.

Older adults aged 60–77 who perform low-load resistance training at 40% of their maximum strength twice a week for twelve weeks gain between 21% and 24% more maximal dynamic strength, whether they train to failure, stop early, or use fixed repetitions.

In older adults aged 60–77, 12 weeks of light resistance training at 40% of maximum strength does not increase muscle size, and changes in strength or function during this period are not primarily caused by muscle growth.

This claim says that light weight training doesn't really help older adults get bigger muscles, move faster, or get up and go quicker after doing it twice a week for 12 weeks.