One of the most frequent questions I get in my personal training business is about how frequently should I train each body part. During my competitive years on stage as an IFBB Pro, I trained each body part once per week. Some of the smaller bodyparts such as abs, calves, and arms, every once and a while I would train them twice a week, but only the small body parts, never large muscle groups. Many bodybuilders make the mistake of training a lagging body parts twice a week to make it grow; this is a mistake.
The key to making weak body parts grow is to change your training regimen, either with more sets, heavier weight, change your rest period, change the muscle angles you are performing the exercise, etc. In the words of Eight Time Mr. Olympia, Lee Haney, “Stimulate, Don’t Annihilate.” Training a body part twice a week can lead to overtraining, here is a study published in the Scandinavian Journal of Medicine and Science in Sports to support my theory on once a week training.
In the 2011 study, researchers had eight men perform two exercise bouts (with 48 hours rest in between training sessions) consisting of three sets leg extensions until exhaustion with 40% load.
The researchers were examining anabolic hormone responses in response to training a body part 48 hours after a previous training session. One would think that the twice a week program would lead to an enhanced anabolic response, but it did just the opposite.
After the first training session, the subjects reported muscle soreness, but after the second training session, the subjects had reduced muscle strength but more importantly a reduced anabolic response to the second training session.
The production of growth hormone decreased by 45 percent less than after the first training session and also adrenal hormones adrenaline and nor-adrenaline were lower as well. This means the men have not recovered the first session and the second training session resulted in a blunted anabolic hormone response that is not good for muscle growth.
In order to make consistent gains, I think training each body part such as the chest, legs, back, and shoulders once per week, because they need at least one week to recover fully but some of the smaller body parts such as arms, legs, abs, and calves can be trained twice a week.