Combining strength training (to promote muscle growth, power and strength) with an aerobic piece (to develop aerobic and anaerobic endurance) is known as combined training. We do this at least a couple of times a week at Integral with the majority of the training we do being mixed modal High Intensity Interval Training. People seem to be unhappy when we program strength only days—usually low repetition heavy lifts—as compared to those days when the workout is a 20+ min. grind. However there is growing research evidence that suggests that combining training this way produces less than optimum strength gains. The evidence points to what is called the “interference” effect.
The explanation of the interference effect is that aerobic training requires an adaptation that is different than what strength requires. This sets the body up for a conflict of interest, which is mitigated by the last stimulus winning. So, if we lift then do a MetCon, the building materials that would have gone to strength will go to the building more slow twitch fibers needed for endurance, then the fast twitch fibers required for strength. This is one explanation why people who do CrossFit style training—mixed modal—don’t get that big, as compared to people who only do resistance training, for instance.
Resistance training is known to increase protein synthesis for up to 72 hours. In other words resistance training will build muscle for up to 72 hours and needs that time to “recover” stronger.
On the other hand aerobic exercise tends to inhibit protein synthesis—you don’t see big marathoners for a reason—which is at odds with strength training.
The problem is complicated further by not being able to reverse the order of exercises: aerobic followed by strength, since the strength training needs to be done with a relatively fresh muscle. We don’t want to train lifts when we’re tired for technique reasons as well as the ability to lift heavier. A strength progression requires that we increase the load.
The optimal situation is to break up your strength and aerobic training by at least 8 hours. But that’s not real for most people. As a compromise we program a “lighter” METCON after a heavy lift session—it might not feel like it. And we always put the strength component before the MetCon.
People with Individual Program Design, can make use of the Open Gym times to get their strength training to separate it from the aerobic training. You can also decide that you’re not going to go hard after a heavy lifting session. Going “hard” to where you’re smoked after the work is does not increase your aerobic endurance.
You can also maximize your protein consumption after a lifting session—I like the SFH Recovery drink since it also aides in recovery.
The recommended protein intake after a strength session is 0.2 grams / kilogram of body weight.