How does exercise order in a workout affect hypertrophy?
Except in certain rare cases, each workout in a training program includes a number of exercises. When writing the training program, we must therefore decide the order in which to perform the exercises in each workout.
Instinctively, we tend to prioritize exercises, placing the ones we consider to be most important at the start of the workout, and the others later on. Currently, some researchers agree with that approach, while others recommend always performing multi-joint exercises first.
So who is right?
What do experts currently recommend?
There are two common recommendations regarding exercise order.
The traditional recommendation is to perform multi-joint exercises first, and single-joint exercises that train the same muscle group afterward. How to order several multi-joint or single-joint exercises (or exercises that work different muscle groups) is not specified in this framework.
More recently, it has become popular to recommend performing exercises that work the muscle groups that are the main priority first, regardless of whether training those muscle groups involves multi-joint or single-joint exercises.
So what is the logic behind these recommendations?
#1. Multi-joint exercises first
Multi-joint exercises involve prime mover muscles working at two or more joints. For example, the bench press involves prime mover muscles working at the shoulder and the elbow, while the squat involves prime mover muscles working at the hip, knee, and ankle.
When we perform a single-joint exercise first in a workout, this can limit the number of reps that are achieved in a multi-joint exercise that is performed afterward, by fatiguing one of the prime mover muscle groups that is used.
Some researchers have suggested that this reduction in exercise performance causes the other (not fatigued) prime mover muscle groups to experience lower levels of motor unit recruitment in the multi-joint exercise, than they would if the single-joint exercise had not been performed beforehand. In this model, the ability of the fatigued muscles to produce force is assumed to limit the ability of the non-fatigued muscles to reach muscular failure, which stops them from achieving full motor unit recruitment.
In contrast, this problem is supposedly not experienced when the multi-joint exercise is done first in a workout. Fatiguing the prime mover muscle group of a single-joint exercise by working it beforehand in a multi-joint exercise will not affect the ability of that muscle group to reach muscular failure, since it alone is the limiting factor for the performance of the exercise.
The key limitation with this model is that it ignores the fact that fatigue can occur in the central nervous system and also inside the muscle, and the origin of the fatigue affects the level of motor unit recruitment that is reached when training to muscular failure.
Indeed, we know that during strength training, fatigue arises both within the central nervous system and also within the muscle. When fatigue arises in the central nervous system, this prevents full motor unit recruitment from being reached. Consequently, exercises that are performed later in a workout are less likely to experience full motor unit recruitment than those that are performed earlier (regardless of whether they are single-joint or multi-joint exercises), since more central nervous system fatigue will be present.
#2. Exercises that work priority muscle groups first
More recently, researchers have recommended performing exercises that work those muscle groups that are the lifter’s main priority first, regardless of whether training those muscle groups involves using multi-joint or single-joint exercises.
This recommendation is based on some studies reporting that performing triceps extensions earlier in a workout leads to greater triceps brachii muscle growth, compared to when performing the bench press first. Moreover, other studies have reported greater maximum strength and repetition strength gains in those exercises that are performed first in a workout, compared to when they are performed later.
At face value, this recommendation overcomes the key limitation in the traditional model, which is that central nervous system fatigue can occur in those exercises that are performed later in a workout, and this will reduce the level of motor unit recruitment that is reached by those exercises in the worked muscle groups when training to muscular failure.
However, the alternative model does not recognize the fact that there is still a difference in the contributions of each type of fatigue to task failure between multi-joint and single-joint exercises.
In any exercise, task failure is reached when we are unable to produce the required level of force to complete the next rep of the movement. The level of force we can exert is determined by the amount of fatigue that is present, and this fatigue is made up of multiple components, including processes within the central nervous system and inside the muscle.
In general, the less muscle mass that is worked by a movement, the greater the local muscular fatigue.
Indeed, single-joint exercises involve greater local muscular fatigue than multi-joint exercises, one-limb exercises involve greater local muscular fatigue than two-limb exercises, and upper body exercises involve involve greater local muscular fatigue than lower body exercises. This suggests that multi-joint exercises may be limited more quickly by central nervous system fatigue, possibly due to the greater aerobic demand (aerobic exercise seems to cause central nervous system fatigue more readily than strength training) or greater degree of blood lactate accumulation. However, the practical implications of this difference between exercise types are unclear.
N.B. Research limitations
To date, few long-term studies have been performed that have measured the effects of training with different exercise orders. Moreover, these studies have either only measured those muscle groups primarily targeted by single-joint exercises, or they have not been clear about which muscle group is being measured (multi-joint leg extension exercises such as squats and leg presses primarily target the single-joint quadriceps, while the knee extension exercise primarily targets the rectus femoris).
What does this mean in practice?
The key factor that determines whether a multi-joint exercise should be placed first in a workout is likely the ability of that exercise to cause full motor unit recruitment in the muscle being targeted.
For example, the squat and leg press seem to be more effective for developing the quadriceps than the hip extensors, which likely means that the quadriceps achieve full motor unit recruitment during these exercises, while the hip extensors may not. Conversely, the bench press seems either similarly effective for the pectoralis, shoulder, and triceps muscles, or superior for the pectoralis and shoulder muscles than for the triceps muscles. On balance, it seems likely that the pectoralis major (and anterior deltoid) achieve full motor unit recruitment during this exercise, while the triceps does not, except perhaps when very heavy loads are used.
When performing the squat or leg press first in a workout, the quadriceps are loaded maximally. In contrast, when performing the bench press first in a workout, the triceps brachii are not loaded maximally, since they are not the limiting factor for the exercise. In both cases, the quadriceps and triceps brachii experience central nervous system fatigue in the subsequent single-joint exercises (the knee extension and triceps extension), and therefore may not reach full motor unit recruitment in that single-joint exercise. And this means that the quadriceps reach full motor unit recruitment in the workout, while the triceps do not.
Consequently, performing the squat or leg press first in a workout (and the knee extension second) might develop the quadriceps more effectively than the opposite order, while performing the bench press first in a workout (and a triceps extension second) might not develop the triceps as effectively as the reverse order, but it might lead to greater pectoralis major development. And this is broadly what the research shows.
What is the takeaway?
Central nervous system fatigue accumulates over the course of a strength training workout, and this reduces our ability to recruit high-threshold motor units when training to failure. Consequently, muscles that are loaded by exercises performed last in sequence will likely grow less than those that are loaded by exercises done first. To ensure optimal results for those muscle groups that are the main priority, exercises that target those muscles should be performed first in a workout, and care should be given to understand the role of each muscle in multi-joint exercises, when they are placed first.