When I was younger I used to train with my brother. And we would follow a typical bodybuilding split. What I mean by that is that our training days were divided up based on body parts and certain exercises.In other words our workouts might have looked something like this:

Day 1 - legs, arms and abs

Day 2 - glutes, chest and abs

Day 3 - back, shoulders and abs

A few things should jump up at you right away. First of all, what does 'legs' mean? Is this quads, hamstrings or calves? Or all three?Apparently abs were really important with bodybuilding and they never require a rest day. And getting huge, or swole as the kids now like to say, was priority numero uno. No one did cardio.

A warm-up involved a few light sets under the bar before starting in with the first sets of bench press. There was zero stretching or mobility work. And although we did abs it was mostly to target the rectus abdominis, or six pack. We didn't know or care about the core at all.

We took rest days when the gym was closed. Otherwise it was simply rotating through this three day rotation looking to add load to the bar at every workout.

Although we now know this to be terrible programming it's surprising what hard work over time will achieve. When Jon went to depot for the RCMP I believe he put some lifting records in the weight-room.

But we could have gotten even better results. And a study from a few years ago might have given some clues as to how often we could train certain movements and muscles.

What the researchers did was look at muscle damage to the arms and legs after training. They wanted to know if there was a difference in recovery between smaller (arm) and bigger (leg) muscles.

17 test subjects performed eccentric flexion and extension for the arms and legs. Eccentric arm flexion would be opening the elbow as if lowering the weight after a biceps curl. Eccentric arm extension would involve straightening the arms from a bent elbow position. With the legs eccentric knee flexion is lowering the body during a squat. And eccentric hip extension is moving the hips back into a flexed position.

Here's what they found.

The arms were slower to recover than the legs. The triceps recovered slightly more quickly than the biceps. And with the legs the knee extensors recovered more quickly than the knee flexors.

As for how long the recovery took the knee extensors showed to be ready to go again within a day. The knee flexors took up to 4 days to recover. As for the arms, even after 5 days there still wasn't complete recovery. Recovery was considered in terms of return of strength as a reflection of muscle damage.

What does this mean?

Even though the study used sedentary subjects we would expect similar patterns for trained subjects and athletes. In other words legs will recover more quickly whether you are well trained or not. Recovery would happen sooner for athletes and trained individuals though.

In terms of exercise selection you should be OK to train the knee extensors more frequently. So you can squat a few times per week if you'd like to. Just make sure to mix up the rep range, the number of sets and intensity. Deadlifts are more taxing on the body and take longer to come back. With four days for the knee extensors to come back this means at most you could deadlift twice per week. And with elbow flexors i.e. taking 5 days this makes it difficult to train biceps specifically more than once a week.

Reference

1. Chen TC, Lin KY, Chen HL, Lin MJ and Nosaka K. Comparison in eccentric exercise-induced muscle damage among four limb muscles. 2011. European Journal of Applied Physiology. 111(2)211-223.