A long-standing tenet in bodybuilding is that if you want to promote muscular hypertrophy, or muscle size gains, you need to train heavy, using lower reps. Conversely, training with lighter weights will “tone” muscles, but isn’t effective for promoting gains in muscular size and strength. Much of this is based on a physiological principle called the Muscle fiber recruitment hierarchy. This principle states that the body activates only as many muscle fibers as possible to produce movement, beginning with the slow-twitch, or type-1 muscle fibers. As these fibers fatigue (and fatigue is the key word here, as we shall see), other muscle fibers, namely types 2-a and 2-b, also known as fast-twitch muscle fibers, are brought into play. What activates these fast-twitch fibers are neuromuscular connections. Simply put, when enough resistance is placed on the muscle, a signal is sent to the cerebellum section of the brain requesting more neural input to the muscle fibers in order to recruit the type-2 fibers. For years, it was thought that to recruit the type 2B muscle fibers required a greater neural input, and the best way to do this was to increase the intensity level of the imposed stress on the fibers. The best way to do this was to lift heavy. Indeed, most exercise physiology textbooks say that the fast-twitch type-2 muscle fibers are the fibers most amenable to gains in muscle size and strength. Type-1 slow-twitch fibers are more related to endurance, and would be activated with lower intensity exercise, such as when doing endurance activity, or when using lighter weights for higher reps. Again, it was thought that the body won’t recruit the type-2 fibers unless it was necessary. But note that the type-2 fibers can also be brought into play when the type-1 fibers become fatigued, for whatever reason.
Bodybuilders had larger muscles because of a selective hypertrophy of type 2B fast-twitch muscle fibers, and they achieved this through lifting heavy weights. But in recent years, this notion has come into question. As I reported in an Ironman magazine article a while ago, muscle biopsies of champion bodybuilders showed that they had a preponderance of type 2A fast-twitch muscle fibers, rather than the expected type 2B fibers. Type 2A fibers are considered an intermediate fiber, having characteristics of both type 1 and type 2 fibers. What this pointed to was that the typical bodybuilding workout of doing higher reps, averaging 8-12 per set, would likely produce better muscle gains compared to doing lower reps with heavier weight.While many powerlifters and Olympic weightlifters undeniably are strong, many don’t show the level of muscle hypertrophy that you would expect considering their chronic heavy lifting training routines, which usually involve heavy weights and low reps.
Occlusion training, which involves training with an impediment to blood flow, such as wearing an inflatable cuff while training, has been shown in several studies to produce significant gains in muscle size despite using light weights. Various reasons are offered to explain this effect, but the main mechanism seems to be an increase in localized fatigue products produced in the muscle as a result of the impeded blood flow. This increased fatigue, in turn, is interpreted by the brain as a call to recruit the type-2 muscle fibers, which result in the muscle gains apparent following this type of exercise. I also reported on another study, in which subjects lifted light weights, but under high tension, meaning that they did the exercises slower than normal, and forcefully contracted the trained muscles during every rep. Again, despite using weights only equivalent to 20% of one rep-maximum, which is very light, the subjects made gains in muscle size comparable to that achieved through lifting far heavier weights. The deciding factor here was again the level of local muscle fatigue produced in the trained muscle, which not only fully activated the type-2 fibers, but also promoted a greater release of anabolic hormones, such as growth hormone and IGF-1, which are stimulated by locallly produced muscle fatigue factors, such as increased lactic acid in the muscle.
In the latest study, 15 men, average age, 21, all of whom had at least 6 months of training experience, and had trained at least three times a week 6 months prior to the start of the study, did 4 sets of one-legged extensions using differing training protocols. These protocols were as follows:
1) 90% of one-rep maximum weight to failure (heavy weight)
2) 30% of one-rep maximum matched in reps and load to #1
3) 30% of one-rep maximum done to failure (light)
The scientists conducting the study calculated various rates of protein synthesis in the trained muscle, measuring both contractile protein synthesis and connective tissue or structural muscle protein synthesis. Increased muscle protein synthesis is directly related to increased gains in muscle size and strength, particularly the contractile proteins. The study results showed that the light weight to failure style (#3) was more effective at increasing muscle protein synthesis compared to #1, or high load, heavy weight. The light training to failure produced a level of muscle protein synthesis that was similar to that of the heavy load 4 hours after exercise, but it was sustained for 24 hours after training only in the light weight to failure training. The study authors suggest that the increased volume of training produced by the lighter weight to failure study resulted in more muscle fatigue, and more positively affected the amplitude of the muscle synthesis process. Only the #3 style of training produced sustained increases in the muscle protein synthesis rate of all proteins found in muscle: contractile, connective tissue, and mitochondrial. This means in simple terms that this style of training may be capable of increasing muscle size, strength, and even endurance simultaneously. The total number of completed reps was 94 in group #3; 19 in #1; and 62 in #2. The greater number of reps in #3 appeared to promote a greater activity of several muscle protein synthesis signaling factors. Group#3 also showed higher indicators of signaling factors for stimulation of muscle satellite cell activity, which is important for promoting muscle size and strength gains.
The authors suggest this information could be useful for prescribing exercise for those who are injured or too old to lift heavy weights.They point out that people over age 70 show an anabolic resistance to weight-training, meaning that they don’t show any significant increases in muscle protein synthesis following weight-training. This resistance,however, can be overcome by increasing the volume of exercise in the aged. This jives with the findings of this new study, which suggests that lifting lighter, but doing reps to muscle failure, is capable of fully turning on the muscle protein synthesis machinery of the body. The key is to induce enough fatigue in the muscle to kick-start the muscle protein synthesis reactions. And according to this study, it can be done by using lighter weights that feature higher reps to failure (reps in the study averaged 34 reps per set in the light weight to failure sessions). I believe that a key element of these findings is that even in the light weight group, each set was done to muscular failure, no matter how many reps that took. Just lifting light weights and not training to failure won’t do diddly squat in promoting muscle gains, since it won’t activate the muscle protein synthesis signaling factors that play a central role in producing muscle gains.
Burd, M, et al. Low-load high volume resistance exercise stimulates muscle protein synthesis more than high-load low volume resistance exercise in young men.Plus One 2010;5:e12033.
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