By STEVEN J. FLECK, PHD Musclular Development
Q: Some lifters at my club 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. I did not notice much difference between my muscle size gains with either type of program. What does sport science research say about how many days per week a muscle group should be trained?
A: 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 favorite athlete. If their favorite athlete trains a muscle group one time per week, they will adapt a similar training program. Similarly, if the training frequency of their favorite 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.
So most people look at training frequency in terms of how many days per week a particular muscle group is trained and not as how many days per week training takes place on. 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 though 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. Thus, whenever trying to come to a conclusion concerning training frequency, other training variables need be considered and do possibly affect the conclusion about the optimal training frequency for muscle size gains.
Swedish researchers recently published a review of the sports science research concerning muscle hypertrophy to reach a conclusion trying to consider not just training frequency, but all the other training variables that might affect any conclusion concerning the optimal training frequency. The majority of research projects concerning training frequency have looked at either the quadriceps or the biceps muscle group. So, these Swedish researchers chose to examine only studies that trained these two muscle groups. For quadriceps training, there was no difference between training two or three days per week, with both frequencies showing a daily increase of 0.11 percent in muscle size. For the biceps muscle group there is also no difference between training frequencies of two or three days per week, with an average increase of 0.18 percent per day in muscle size. It is interesting to note that these researchers found no studies examining muscle size increases with a training frequency of one day per week. They did find several studies training for five days per week. Thus, although they conclude that there is no difference in muscle size gains between frequencies of two and three days per week, they also concluded that muscle size gains can be made with training frequencies of anywhere between two and four times per week for as long as six months. So more research is badly needed concerning the effect of training frequency on muscle size gains, especially on the aspect of less frequent and more frequent training sessions than two or three days 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 a 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.
Many times, discussions about training frequency eventually mention evidence of bodybuilders training a muscle group only once or twice per week and the athletes, such as Olympic weightlifters, performing exercises that involve a muscle group like the 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 exercises: 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 and Olympic weightlifters many times train daily. Some bodybuilders train using body part routines, where a muscle group is emphasized or the focus of training only one day per week. Many variations of body part routines are possible, but the major aspect related to training frequency is a body part or muscle group is only emphasized one or two days per week of training. Both bodybuilders and Olympic weightlifters have a great deal of hypertrophy. So, comparison of their different training routines makes it difficult to come to a conclusion concerning the effect of training frequency on muscle size gains. One aspect that could be involved when talking about training programs of athletes is how experienced they are at weight training. 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 muscle 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. This is even true when weekly training volume is the same. This information indicates that training a muscle group more than one time per week increases muscle size more than training only one time per week.
The effect of training frequency on muscle size gains definitely needs more research. This is especially true when it comes to the optimal training frequency of elite athletes, in part because many athletes who train a muscle group only one day per week do so with a very high training volume (several exercises for a muscle group and net assets of each exercise) per session. With a very high training volume per session, there may be need of a longer recovery time between training sessions. It must also 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. There may also be differences in the optimal training frequency for muscle size gains depending upon where you are in your training. For example, a very high frequency in combination with a relatively low-to-moderate volume per training session may be a good way to "kick-start" muscle size gains either at the start of a training program or if you are in a training plateau. This last point brings out the idea that some type of planned variation or periodization of training may be necessary to maximize muscle size gains. This could mean changing up the exercises for a certain muscle group, changing the number of sets, repetitions and weight used for different exercises, as well as changing training frequency for a muscle group in order to bring about long-term increases in muscle size over months or years of training.
Wernbon M, Augustsson J and Thomee R. The influence of frequency, intensity, volume and mode of strength training on a muscle cross-sectional area in humans. Sports Medicine, 37:225-264, 2007.