By Brad Schoenfeld, Ph.D., CSCS, FNSCA
Going back to the early days of fitness, competitors routinely trained using full-body routines. The idea was that frequently stimulating muscles throughout the week was the best way to increase lean muscle without overtraining.
By the 1960s, training philosophies began to change. Full-body routines gave way to training splits, where the goal is to work a muscle using multiple sets and exercises, and then afford the muscle with as much as a week’s recovery before it’s directly trained again.
More Training Volume Per Muscle Group
The theoretical benefit of a split routine is that it allows total weekly training volume per muscle group to be increased, while providing muscles greater recovery for growth. In addition, working a muscle with a high training volume in a given session heightens intramuscular metabolic stress, which in turn is believed to enhance the hypertrophic response. The combination of these factors are thought to ultimately lead to greater long-term lean muscular gains.
Although a case can be made for using either full- or split-body routines to increase lean muscle, an evidence-based opinion can only be formed by first evaluating the results of controlled research. Given that training frequency is one of the most important training variables, you’d think there’d be a ton of studies conducted on the topic, right?
Until recently, only one study actually compared the muscle-building effects of training muscles one versus three days per week. Subjects either performed three sets per exercise in a single weekly session, or one set per exercise spread out over three weekly sessions for 12 weeks. At the completion of the study period, results showed greater increases in lean body mass for the three-day-a-week group, indicating a benefit of training muscles more frequently. While the study is intriguing, there are some inherent limitations that hinder the ability to draw practical conclusions. For one, subjects performed only three sets per muscle group per week— far below what most serious fitness enthusiasts typically include in their training programs. For another, muscle mass measures were assessed by the skinfold technique, which lacks precision in determining true changes in hypertrophy over time. The applicability of the study to serious lifters seeking to maximize muscle building is therefore limited.
Splits vs. Full-Body Routines
To gain clarity on the topic, my lab recently carried out a controlled study that compared muscular adaptations in a typical split versus a full-body routine in well-trained lifters. Both routines comprised 21 different exercises that targeted the major muscle groups using multi-set routines. Those in the split routine performed chest and back on day one, lower body on day two and shoulders and arms on day three. Alternatively, the full-body routine consisted of performing one exercise for all the major muscle groups during each session. Training was carried out three days per week for eight weeks. Total volume was equated between routines so that any differences in muscle development could be attributed directly to the effects of training frequency. Changes in muscle size were assessed by ultrasound to provide direct hypertrophic measurements. Subjects had more than four years of lifting experience, thus ruling out any issues from the “newbie effect.”
The surprising results challenge current training practices.
Those performing the full-body routine experienced significantly greater increases in biceps growth compared to split-body training (6.5% versus 4.4%, respectively). Although differences in the other muscles analyzed were not statistically different, the increases favored the full-body routine for both the triceps (8.0 versus 5.0%, respectively) and the quads (6.7 versus 2.1%, respectively). Moreover, determination of effect size— a statistical gauge of the meaningfulness of results— showed a clear advantage for the full-body routine in all of the muscles we measured. These findings suggest a benefit to training a muscle more often over the course of a week.
Time to Ditch the Split?
There is a logical basis to training muscles more frequently each week. This is consistent with the fact that muscle size is regulated by the dynamic balance between muscle protein synthesis (MPS) and protein breakdown. Simply stated, when MPS is greater than breakdown, there is a net accumulation of skeletal muscle mass; the more you can maintain high levels of MPS over time, the greater your gains. Research shows that the time course of muscle protein synthesis (MPS) lasts about 48 hours or so following a lifting session. It’s therefore reasonable to conclude that training a muscle every few days would keep MPS consistently elevated, and thus have a positive effect on lean muscle development.
Before you ditch the split, however, it’s important to consider a couple of things. First and foremost is the novelty factor. Prior to training, we conducted pre-study interviews about training history. During these interviews, 16 of the 19 subjects reported regularly employing a split routine, with each muscle group trained once per week. Research indicates that simply changing program variables so that a new stimulus is provided can enhance muscular adaptations. This raises the possibility that those in the full-body training group benefited from the unaccustomed stimulus of training muscles with a greater weekly frequency.
Train Muscles More Frequently to Maximize Lean Muscle
Perhaps more importantly, the study needs to be taken in the context that volume was equated between groups. A primary benefit to training with a split routine is that it allows more volume to be packed into workouts over the course of a week. Assuming 48 hours is afforded between training a given muscle group— a generally accepted tenet— then full-body training limits you to three weekly sessions. Alternatively, splitting the routine lets you up the frequency of sessions per week, and thus allows you to achieve more volume per muscle, per session. Given that higher training volumes are strongly associated with greater lean muscle growth, the potential value of training splits should not be discounted.
Bottom line: Research shows a benefit to training muscles frequently throughout the course of a week. Although evidence is somewhat limited, it would appear that at least twice-weekly stimulation of a given muscle is beneficial to maximize lean muscle growth. This can be accomplished with an upper body/lower body split carried out four days per week (i.e., two days on/one day off, two days on/two days off) or a three-way split (i.e., push/pull/legs) performed six days per week (i.e., three days on/one day off). It’s also possible that periodizing training frequencies might provide a means to maintain the novelty of the training stimulus. Accordingly, consider integrating full-body workouts into your programming over the course of a training cycle to enhance the hypertrophic response.
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