Importantly, subgroup analysis revealed that conclusions strengthened when direct measures of muscle growth such as magnetic resonance imaging and ultrasound were separated from less accurate indirect measures such as dual energy X-ray absorptiometry, and air displacement plethysmography (BodPod). These findings lend strong support to the claim that volume is a primary driver of muscle hypertrophy. It should be noted that the data were insufficient to determine whether more than 10 weekly sets per muscle provided additional hypertrophic benefits and, if so, at what point a threshold exists.