Muscle Hypertrophy and Strength Adaptations to Systematically Varying Resistance Exercises

We compared the effects of varied and constant resistance exercises on muscular adaptations in young women. Seventy young women (21.8 ± 3.4 yrs, 62.0 ± 12.3 kg, 162.3 ± 5.7 cm) were randomly divided into two groups: constant resistance exercises (CON-RE, <i>n</i> = 38) or varied resistance exercises (VAR-RE, <i>n</i> = 32). The resistance training (RT) was performed thrice a week over 10 weeks. CON-RE performed a 45º leg press and stiff-leg deadlift in every training session, while VAR-RE performed 45º leg press and stiff-leg deadlift in the first training session of the week, hack squat and prone leg curl in the second, and Smith machine squat and seated-leg curl in the third. Both groups performed two sets of 10-15 repetitions maximum per resistance exercise. We measured the muscle thickness of the thigh's anterior, lateral, and posterior aspects by ultrasonography at different muscle sites (proximo-distal). Muscular strength was analyzed from the one-repetition maximum (1RM) tests in the 45° leg press and leg extension (non-trained exercise). The muscle thickness increased similarly in both groups for all muscles and sites (CON-RE: +7.8-17.7% vs. VAR-RE: +7.5-19.3%, <i>p</i> > .05). The 1RM increased similarly in both groups (CON-RE: +24.4-32.1% vs. VAR-RE: +29.0-30.1%, <i>p</i> > .05). Both RT routines resulted in virtually similar muscular strength gains and hypertrophy. Therefore, both strategies should be considered for the improvement of strength and muscle growth.