Some people at my gym train a muscle group several times per week, while others train a muscle group only one time per week. Both the lifters who train a muscle group one time per week and multiple times per week claim that their training program is best for muscle size gains. I have trained using programs with one session per week for a muscle group and with two or three sessions per week that with some exercises involve the same muscle group.
Training frequency - overview
Training frequency is an important consideration when training for muscle size. What people think is the best training frequency is many times affected by the training frequency of their favourite athlete. If their favourite athlete trains a muscle group one time per week, they will adapt a similar training program. Similarly, if the training frequency of their favourite athlete is three times per week, they will train three times per week. Training frequency needs to be defined, because without a standard definition, information concerning training frequency can become confusing. For most people, training frequency means how many times per week a particular muscle group is trained. This definition is important, because it would be possible to train six days per week and only train each muscle group one day per week or train each muscle group two, three or even six days per week with six training sessions per week.
Researches and clinical studies
Quite a bit of research has been done investigating the effect of training frequency on hypertrophy or muscle size. However, when looking at this research, unfortunately other factors than frequency need to be taken into consideration when trying to reach a conclusion about what is the optimal frequency when training for muscle size increases. For example, it would be possible to train a muscle group two days per week with 4 sets of each exercise or train the muscle group one day per week with 8 sets of each exercise. Assuming number of repetitions and the weight used for each set was approximately equal, total training volume (sets x repetitions x weight) performed per week would also be approximately equal. So even training frequency was different, training volume is the same. Obviously many combinations of number of sets, number of exercises and weight used could be used to make up one or any other number of training sessions per week.
One consideration when thinking about long-term muscle size gains is how long after a weight-training session muscle protein synthesis goes on. How much net muscle protein synthesis goes on after each training session will affect muscle size gains over the long haul. After weight-training session, peak protein synthesis rates take place somewhere between 3 and 24 hours after the training session. Muscle protein synthesis increases above resting values are apparent for as long as 48 to 72 hours after a training session. One might interpret protein synthesis rates to mean it does not pay to perform another training session until after protein synthesis rates have returned to normal or are no longer at peak values. Although this might make sense, current information concerning protein synthesis rates could be interpreted to mean that you should train a muscle group anywhere between every day (protein synthesis rates peak within 24 hours after a training session) or approximately two times per week (protein synthesis rates are increased for as long as 72 hours after a training session). So more research is definitely needed concerning the effect of weight training on protein synthesis rates and the long-term effect on muscle size gains.
What our muscles can tell us?
Bodybuilders train a muscle group only once or twice per week and the athletes, such as Olympic weightlifters, performing exercises that involve a muscle group like quadriceps several times per week or in some cases almost daily. Every training session for an Olympic weightlifter will normally include several of the following exercise: back squats, front squats, variations of the Olympic lifts such as clean pulls and snatch pulls, jerks, full cleans and full snatches. All these exercises involve the quadriceps, hamstrings, gluteals, calves and lower back. So these muscles are trained virtually every training session for an Olympic weightlifter.
A training frequency of one time per week has been shown to increase muscle size and fat-free mass. This, however does not mean that a training frequency of one time per week is optimal; it only means that it does result in some muscles size gains. Some information from studies does indicate that with experienced weight trainers, greater increases in fat-free mass take place with three training sessions per week, compared to one training session per week per muscle group.
With a very high training volume per session, there may be need of a longer recovery time between training sessions. It must be remembered that simply because one training session per week does result in an increase in muscle size, it does not mean that it is the maximum or optimal increase in muscle size.