Introduction
With Exercise, we perform movements that engage and fatigue specific muscles. To choose the best exercise program, we must first test which actions engage the targeted muscles most efficiently and safely. That is why exercise selection is essential. Yet, we move one joint in some movements – single-joint, and in others, we move two or more joints – multi-joint. And it is this disparity in the number of joint rotations that is the focus of this post.
Muscle isolation
Exercise can be divided into single and multi-joint exercises. The main difference between the two is the precision of accumulating muscular fatigue. Single joint exercises involve one major muscle, while multi-joint involve two or more.
MORE MUSCLES INVOLVED, LESS SPECIFICITY
In general, the greater the number of muscles involved, the lower the specificity. That means that our energy and focus are spread over a larger area. The specificity of fatiguing targeted muscles is also called muscle isolation. Muscle isolation can only be an interval value due to interwoven muscles and related to joints. That means there is no exercise, which fatigues only one muscle group. Other muscles will always be involved; it is either to help the movement, stabilize the rotating joint or stabilize the required body posture.
The big difference between single-joint and multi-joint exercises
The number of joints being involved measures the complexity of Exercise. The more joints involved, the more muscles are engaged. This is great since we can fatigue more muscles at once, which increases our time efficiency. But, the more active muscles, the less specific the Exercise is to one area. As a result, choosing between single or multi-joint exercises is a matter of specificity against time efficiency.
SINGLE-JOINT EXERCISES ESTABLISH DEEP FATIGUE
When only one joint is moving, one muscle group is primarily fatigued. When we reach deep fatigue, the fatigue accumulated is mainly in this one muscle.
IN MULTI-JOINT EXERCISES, SOME MUSCLES FATIGUE LESS THAN OTHERS
On the other hand, a multi-joint exercise includes many joints and, as a result, fatigue more muscles at once. However, some muscles will fatigue faster than others if not using an appropriate form. This means that when we reach the point of momentary muscular failure, we will probably reach it on one muscle, but not all of them. Some muscles might not even get enough stress to make them adapt and improve.
For that reason, most of the exercises involve rotations at 1 to 3 joints. Everything else is probably not an appropriate exercise movement since the muscular fatigue is spread out too much [2].
Single-Joint Exercise
Single-joint exercises are known by two other names; simple or isolation exercises. In a single-joint exercise, movement happens around one joint. For that reason, one major muscle is active and tired. Single-joint exercises are ideal for rehab because they focus on one area while avoiding others. This is helpful when we have an injury or a lagging body part. There is a single-joint exercise for every major muscle. Certain muscles, particularly stability muscles, can however only be fatigued with a single-joint exercise.
The purest form of muscle isolation
As noted before, single-joint exercises primarily fatigue one muscle group. Because of that, it is much easier to keep the mental focus on that area while exercising. This also leads to the fact that we can establish an excellent mind-muscle connection much easier [3]. Because of fewer joints involved, it is also less likely to mess up the form and, in that regard, risk an injury. Thus, single-joint exercises are more effective in fatiguing specific muscles, and they are easier to learn and execute the correct movement.
Multi-joint exercises
Different than single-joint exercises, multi-joint exercises involve motion around many joints. As a result, a lot of muscles are activated and fatigued. Ideally, all the muscles involved are fatigued at the same rate. By doing so, we fatigue numerous muscles with only one exercise. This saves time over conducting separate exercises for each muscle group. Yet, it is essential to note that the rotations in multiple joints need to happen at once and not one after another.
COMBINING MULTIPLE EXERCISES IN ONE, REDUCES ITS EFFECTIVENESS
For instance, doing a movement where we first squat and then lift overhead is an activity combining two separate movements. While each Exercise is multi-joint and fatigues many muscles in the lower and upper body, the depletion does not build efficiently. We fatigue one set of muscles first and then another set. This makes it hard to accumulate deep muscular fatigue. Because of that, those types of activities are inappropriate for Exercise.
Multi-joint exercises are great for time efficiency
As noted in the previous sections, the main benefit of multi-joint exercises is time efficiency. With a handful of such exercises, we can fatigue and stimulate most of the muscles in our body. If we perform the exercises correctly, we can have an effective program with only 3 – 5 exercises and a total exercise time of 5 – 10 minutes. If we manage to fatigue muscles to a high level, we don’t need to repeat this workout for another week. That type of efficiency is hard to beat.
For best overload, limit the range of motion
Throughout the movement, muscles change their length. By this, muscles become more or less efficient at overcoming stress as their length changes. When we execute improper movements or use an extreme range of motion, the active muscles are unable to absorb the force demands. The resistance is moved to other areas, such as the deeper stabilizer muscles, tendons, and joints. This can shift the muscular tension, create impingement, spasms, and inflammation. The issue of overloading our muscles in extreme ranges of motion is troublesome for both muscle types. The danger is valid for both groups of muscles. However, it occurs with exercises for superficial muscles most of the time. The best antidote to this issue is to limit the range of motion [1].
Use active insufficiency to target the stabilizer muscles
While some single-joint exercises can isolate the stabilizer muscles, we can also use multi-joint exercises to achieve the same result. We can strategically use the technique mentioned in the previous paragraph. To fatigue stabilizer muscles in isolation, we need to prevent the stronger superficial muscles from engaging and helping with the load-bearing. To achieve this, the superficial muscles can be placed in a state of active insufficient. This is a position from which they cannot contract any further. Active insufficiency is most of the time reached at the end of the range of motion. If we move with control, the load is safely passed to the deep stabilizer muscles in that position. It is worth noting that in this case, we should keep the range of motion specific to the area of active insufficiency for the duration of the Exercise. By doing so, we keep the tension on the targeted stabilizer muscle [4]. This reduced the used resistance since stabilizer muscles are not meant for load-bearing.
Choosing your exercises
The motto of Exercise is brief, intense, and infrequent. We need to prefer specific exercises and use the correct exercise form to follow that. In the case of exercise selection, we first select the most productive exercises. These mainly come from the pool of multi-joint exercises listed above. With a handful of those exercises, we cover most of the major muscles of our body. If we notice that certain muscles are not fully fatigued by those actions, we add specific isolation or single-joint movements. Finally, if we have joint issues, we should include exercises that address those. This covers all the musculature, allowing us to improve our strength and joint stability.
Conclusions
We covered the contrast between single and multi-joint exercises. The primary distinction is that single-joint exercises are more specialized, while multi-joint exercises are more time-efficient. Single-joint exercises are also more beneficial when attention and focus are required on a specific muscle group, due to injury or purpose (sports). Yet, because of time efficiency, the bulk of our exercises should be multi-joint.
Finally, we have outlined how we can fatigue and improve our stabilizer muscles. Adding those is essential when we want to emphasize our joint stability.
