Does the weight on the bar change which muscles work hardest?

Chris Beardsley

Strength coaches spend a lot of time thinking about which exercises they should be using with their athletes, to help them improve sprinting, jumping, and change of direction ability.

When going through this process, they usually compare the movement patterns (and muscle contributions) of the athletic ability that they are trying to improve, with those of the exercise that they are planning to program.

Very rarely do they also consider how the load on the bar affects the movement pattern (and muscle contributions) of the exercise they are thinking about using.

Yet, that is also a key factor.


How does the weight on the bar affect movement patterns and muscle contributions?

The weight on the bar has profound effects on which muscles contribute to multi-joint exercises, both in the lower body and also in the upper body.

In the lower body, there is a fairly common pattern.

For squats, deadlifts, and lunges, movement is produced by a combined effort from the hip muscles (the gluteus maximus, adductor magnus, and hamstrings), and the knee muscles (the quadriceps).

Yet, as we add weight to the bar in each of these exercises, all of the muscles have to work harder, but the hip muscles increase their contribution more than the knee muscles.

So heavy squats, deadlifts, and lunges train the hip muscles more effectively than the same exercises performed with lighter loads.

Similarly, in the bench press, which is a key exercise for the upper body, the movement is coordinated by the pectoralis major (chest), the anterior deltoids (shoulders), and the triceps brachii (arms).

With lighter loads, the anterior deltoids and triceps brachii contribute proportionally less to the movement than the pectoralis major. With heavier loads, the proportional contribution of the anterior deltoids and triceps brachii increases.

So heavy bench presses are more effective for focusing on the anterior deltoids and triceps brachii, while bench presses with lighter weights are more effective for focusing on the pectoralis major.


What does this mean for your training program?

Although this might all sound like a minor detail, this change in movement patterns (and muscle contributions) of key exercises can really cause some headaches when we are planning strength training.

Let’s say we want to develop change of direction ability in an athlete.

Change of direction ability is primarily determined by the ability to decelerate quickly. Deceleration is achieved first and foremost by the quadriceps (with the hip muscles playing a secondary role). When decelerating, the quadriceps lengthen and exert high forces from short to moderate muscle lengths, and this forces is directed horizontally.

Whenever we have an athletic movement that requires coordinated hip and knee extension, the squat is the first exercise that we go to. And indeed, we can see that the squat movement pattern is quite similar to the decelerating phase of a change of direction maneuver, especially if we overload the lowering (eccentric) phase with weight releasers.

Frustratingly, however, we want to use *heavy* squats to correspond optimally to the high forces that are produced during deceleration. But the squat becomes more and more a hip-dominant exercise as we add load, and it shifts the load away from the quadriceps, where we want it to be. And while switching to front squats might help with this problem slightly, it has less of an effect than you might expect.

So we really need another exercise as well as the squat to challenge the quadriceps with extremely high forces while they are lengthening. And while it may upset some traditionalists, this is probably a single-joint exercise like the reverse Nordic curl, or the flywheel knee extension. And this is simply because multi-joint, lower body exercises shift the system load onto the hips every time we increase the weight.


What is the takeaway?

The weight on the bar has profound effects on which muscles contribute to multi-joint exercises, both in the lower body and also in the upper body.

When programming exercises to transfer to a sporting movement, we need to take a moment to consider whether adding weight is going to improve the focus on the muscle we are trying to develop in the context of the movement pattern, or if it is going to shift that focus somewhere else. If we identify that the focus is being shifted somewhere else, then we can address that with a supplemental exercise.

Chris Beardsley

Written by

Figuring out how strength training works. See more of what I do: https://www.patreon.com/join/SandCResearch

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