The effects of exercise variation in muscle thickness, maximal strength and motivation in resistance trained men
PLOS ONE

I’ll admit that when it comes to movement I tend to focus on endurance over strength. There’s plenty of research, however, that insists on adding some resistance to your training to make you faster and less prone to injury.

This study asked: does randomizing exercises and repetition improve markers of muscular growth and motivation?

21 men were randomized to perform an 8-week resistance training program using either a group of fixed exercises, or exercises that were randomly varied each session via an app (Ace Workout, which costs $2 so of course I haven’t tried it). Both groups performed 3 sets of 6 exercises, 4 days per week.

As expected, both conditions promoted large, statistically significant increases in the bench press and back-squat without differences between groups. They also measured muscle thickness in participant’s quadriceps, and they were the same. Let the gains begin.

One of the main findings here was how the guys who varied their workouts using the app showed a significant improvement in their motivation to train. Less predictability kept things interesting, and kept them engaged.

Takeaway: Strength training should be a weekly component of your movement routine, but it isn’t nearly as fun as riding a bike, so keep it varied. Muscles adapt to load, whether that load arrives through the same exercise or a different one each time. Your mind, however, stays motivated when you mix it up.

This research suggests you keep more complex, free weight exercises (squats, deadlifts, rows, etc) in a regular rotation throughout a training cycle and vary movements that have limited degrees of freedom (leg extensions, machine press, arm curls, etc).