Thought it would be good to get a discusion going about training frequency for bodyparts. I don't know if you have heard of a training program called HST, but the founder claims that science says its best to be hitting a bodypart 3x a week for maximum gains....

Lets get the discussion rolling with a couple of quotes from the man himself...

Whether you are sold on heavy weight and low reps, or less weight and more reps, if your training frequency is not planned with the same scrutiny as other aspects of your routine, you may be wasting time unnecessarily. With a little insight into the factors affecting the optimal timing of your workouts, you may just experience more success than you believed you could.

Knowing exactly when your muscles need to be trained again after the previous workout is difficult to judge with absolute certainty. Recent research in the area of muscle damage and recovery is showing results that may surprise you. Science is now showing us things that may change the way you train forever!

When you lift weights, you cause damage to your muscles. This is often referred to as "microtrauma". Microtrauma involves the tearing and shearing of delicate protein structures within your muscle cells. This may sound bad but in reality it is necessary for the initiation of growth after your workout.

This microtrauma may be expected to require you to postpone your next workout until your muscles are back to normal. It is this logic that your average personal trainer will use when he/she tells you to wait, sometimes a full week, before training the same body part again. Recent research however is showing us that putting off your next workout until your muscles have "fully recovered" may not be necessary or even desirable!1,2,3 In a study performed at the University of Alabama4, two groups of subjects performed the same periodized resistance training routine either once per week or three times per week. The results showed that muscle mass increases were greater in the three workout per week group, compared to the one workout per week group. In addition, the strength increases in this group were on average 40% greater! So what does this mean to you? It means the fear of overtraining, which sometimes verges on paranoia, may be preventing you from getting the most gains you can in the gym.

So science is telling us that training a muscle group approximately every 48 hours may be more effective than training it once or twice per week. If you train your whole body three times per week with your current workout routine it might take several hours to complete. I doubt many of us would have time for that. Does this mean you can't reap the benefits of more frequent training? Once again, new research provides us with some answers.

In a study performed at Montclair State University5 researchers investigated the effect of a single set vs. a multiple set routine on increasing upper body strength. They had the subjects perform either one set or three sets of bench press, incline dumbbell press and flat dumbbell flies using ten reps, three times per week for 12 weeks. This kind of study has been done before but this one is particularly valuable because it involved previously "trained" subjects. This is significant because untrained subjects will usually respond positively to virtually any training routine. Just because a training strategy works for beginners doesn't mean it will work for experienced lifters. These researchers found that doing a single set of each exercise was equally effective as doing three sets of the same movements in increasing the subjects one repetition maximum (1RM) on bench press. The take home message is that you needn't do more than a single work set to achieve the same relative gains of doing multiple sets. This makes incorporating a whole body workout into your schedule much more feasible.
The reason HST calls for more frequent training is because the acute anabolic effects of training, such as increased protein synthesis, muscle-specific IGF-1 expression, and other factors involved in modulation of short term protein synthesis, only last for 36-48 hours. There is also mounting evidence of a "summation" effect by exercising while levels of these signals and responses are elevated, as should be expected.

This does not mean that the structural repairs to the tissue have been completed. Research has demonstrated that you can train a muscle before it is fully recovered structurally and not inhibit its ability to continue to recover. So, HST uses this evidence and calls for repeated loading (training) every 48 hours or so to keep the anabolic activity of the muscle high, while trying to stay slightly ahead of the structural recovery curve by constantly increasing the load each workout. Staying ahead of the structural recovery curve is really key to elicit real growth in a person who has lifted for quite a while. Of course, injuries can develop over time if care isn't taken to take time to heal, and prepare the tendons for repeated heavy bouts of lifting (SD and 15s serve this purpose in HST).

"Recovery" can refer to several different things.

1) "Recovery" can refer to the structural repair process of fixing the microtrauma. The damaged proteins can takes several days to be repaired and all evidence of damage removed. Even at the end of seven days after significant muscle damage from eccentric muscle actions, you may still see some small fibers regenerating.

2) Strength - this can be acute recovery as in the necessary time to rest between sets. Or it can mean the days that it usually takes to regain baseline strength after muscle damaging exercise.

So the trick is to have the CNS "recover" just in time to hit the muscle again as the acute anabolic effects are wearing off. That way you can stay anabolic more of the time. Training once every 7 days will still allow you to grow, it just takes longer for the gains to accumulate. Training more frequently is more efficient if your goal is just to get bigger

To understand, you have to consider the total volume over time. A week is easiest to consider, so, over the course of a week, it is the total volume that is important. So 9 total sets for chest can be done in one workout or in several workouts. Both will stimulate growth. However, you will be anabolic more of the time if you can actually create that stimulus more often. In the case of HST, 3 times as often. There is a physiological benefit (acute anabolic effects of training) in doing 9 sets as 3 sets X 3 workouts, as opposed to 9 sets all at once - and then nothing for the next 7 days.
http://www.hypertrophy-specific.com/...iningfreq.html