With unilateral training you work one limb at a time, doing an exercise that involves one arm or one leg, then exercising the other arm or leg. Just about every bodybuilding training system or routine features at least a few unilateral exercises. A common system is to train a muscle using mostly bilateral (two limbs at a time) exercises, then finish off that muscle group with a unilateral exercise.During his bodybuilding heyday, Arnold Schwarzenegger often ended his workouts with unilateral exercises, particularly when training his arms, his most impressive muscle group. Since Arnold always preferred to train with someone rather than alone, I trained with him several times. In those days he liked to finish his triceps routine with one-arm overhead dumbbell triceps extensions, which he did slowly and with intense concentration. For biceps bent-over dumbbell concentration curls were usually the choice. Arnold performed them using perfect form, full reps with a tight squeeze at the top, or contracted, position of the curl.
Arnold felt that such unilateral exercises had a more concentrated effect on his muscles. The net effect was to instill a huge, satisfying muscle pump that he notoriously compared to an orgasm in the film “Pumping Iron.” While Arnold may have been joking in the analogy, the engorgement of blood that occurred when he did his one-arm curls and triceps extensions wasn’t so far removed from the engorgement that occurs in the so-called love muscle.
Training dogma has it that you can obtain a harder muscle contraction with a unilateral movement than you can by training both limbs simultaneously. From a pragmatic point of view, the brain supplies the neural power to work both limbs for just one limb, making for a tighter muscle contraction.
The effect of training one limb at a time is so potent that some studies have shown a crossover effect in the untrained limb; that is, training one arm or leg at a time makes the other leg or arm stronger even if it doesn’t get direct exercise. Arthur Jones, inventor of Nautilus exercise machines in the 1970s, recognized that and termed it the “indirect effect.”
In one study the untrained arm showed an 8 percent strength increase. Several other studies that examined the training effect found that the amount of strength the untrained limb gains depends on how much stronger the trained limb gets. A recent study, however, noted that those studies were often flawed, and the new study sought to determine whether the crossover strength effect of unilateral exercises was genuine.1
Twenty-one men and 94 women, all untrained, average age 20, engaged in three sets of one-arm curls while not training the other arm. After six weeks the subjects experienced a strength increase of 7 percent in their untrained arms, although those arms got no direct exercise over the course of the study. During a follow-up study, 10 subjects showed a decrease of strength in the untrained arm. The same subjects, however, had the least strength gain in the trained arm, underscoring the results of past studies in which the magnitude of strength gains in the untrained limb depended on how much strength increased in the trained limb.
Interestingly, training faster led to an 11 percent greater strength gain in the trained arm than training at a slower pace did. Despite the gains, no changes occurred in the size of the trained arm, indicating that the strength gains were more related to a greater neural input into muscle than to muscle hypertrophy. What happens is that with increased training, especially with one-limbed exercises, the activation of the muscle motor unit increases, as does the neural firing rate, inducing a more potent muscular contraction. The theory is that one-limbed exercises somehow activate the brain/muscle connection in a manner different from what occurs with two-limbed movements.
Clearly it makes sense to include a few one-limbed exercises in your training routines. Although nearly everyone has one side of the body that’s stronger than the other, the research involving the crossover strength effect induced by unilateral training may compensate for that imbalance.
1 Munn, J., et al. (2005). Training with unilateral resistance exercise increases contralateral strength. J Appl Physiol. In press.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
