This post is on moving our COM (centre of mass) during training and assessment.

During sport and many functional activities such as walking we are constantly moving our COM. Walking is about controlling the change in position of our COM that comes about from the bodies momentum carrying it forward once it gets moving! Try and throw a ball without shifting you COM from the back to the front. The same is true of throwing a punch or hitting a tennis shot. By transferring our COM we are putting the M (mass) in F=MA, Newtons second law of motion that deals with acceleration and ultimately force production. The more mass we can accelerate the more force we can produce. If we threw with just our arm that mass would be small. By moving our entire COM that mass becomes much larger and so does the force we can generate.

The question is do we use transfer of COM in our training and assessment??? A step beyond that is do we displace our mass in the horizontal e.g forward and back, rather than just in the vertical e.g up and down.

How many traditional gym exercises move COM. Well quite a few. Deadlifts and squats both do in the vertical (up and down). How many in the horizontal (forward and back) erm....not so many!! How many of the movements discussed above use forward and back COM transfer for power...all!!! So when we are training for sport really we should be looking to train COM movement away from just the vertical. Does that mean the clean and press is not going to help us punch harder or throw better??, I think that's exactly what it means! We have to examine the functional crossover of our exercises rather than just apply gym based exercises to any sport or function feeling they will have crossover to generic 'strength'

What is described as timing in sport such as when we hit a great shot in cricket or tennis is being able to move our COM at the perfect time in the right direction to impart the most force on the ball!!

Many times during assessment our clients will be able to translate their COM forward effectively on one side but use rotation on the opposite side as they are unable to decelerate the COM transfer in the hip or ankle joint. It is much easier to rotate in the sagittal plane into flexion using gravity and keep the COM central rather than moving the COM forward through translation. A simple test is to see whether a client can lunge forward effectively in the horizontal vector without sinking downwards towards the floor. This would show effective transfer of COM. If we do not look to move COM in assessment we cannot tell if the joints and muscles in question can decelerate our mass and resultant momentum vital to functional success.This deceleration will lead to effective acceleration as we eccentrically load the muscle for concentric force production.

In fact effective horizontal translation in the sagittal plane will increase motion in the transverse plane at the hips and therefore the feet and spine too!

Using 3 dimensional space will force our bodies to shift COM, decelerate and harness momentum for force production. Most traditional exercises keep us rooted to the floor!!

Think outside the box for functional success!!!

This blog comes courtesy of a conversation I had with my good friend Mike. Its all about optimum range of a muscle. It kind of followed on from this piece of info…

The eccentrically-loaded muscle will start its contraction weak and then get stronger; the concentrically-loaded muscle will initiate strong, but get weaker as the contraction continues.

 I had never given this much thought before but this makes a lot of sense when we think of length tension relationships. A muscle will struggle to produce force when both too long and too short.  Being weak in both positions. Cross bridge attachment has an optimal range.  This will be true of both force production and conservation of energy. Too much cross bridge detachment will also cause a more thermodynamically expensive scenario as we split ATP and dissipate energy as heat.

Elastic energy will also I believe have an optimal range. Studies have shown that spring stiffness (ability to return energy) comes from optimal joint angles or ranges. Going beyond this range means that we dampen or absorb energy, again dissipating as heat through visceoelasticity of tissue. Different tissues have varying levels of stiffness and compliance, different ranges will bring into play these different characteristics as will our neurological intention (land or jump again) to move control stiffness through efferent spindle stiffness regulation.

If we look at the way we jump when we want to jump again, we can see that we use a shorter joint range than when we land for the final time.  When we finish we have a large bend of the knee to absorb ground reaction forces rather than reuse them. This has implications for our understanding of height, range and repetition programming for our training me thinks!!

Ecconcentric (both eccentric and concentric muscle contractions occurring in different planes) muscle action may also play a role in optimal cross bridge attachment. If a muscle was to lengthen in all three planes this may cause a scenario where we are going beyond the optimal range for the muscle in terms of force production and elastic energy recoil. By mitigating elongation of the tissue in a plane of motion through concentric shortening we may also keep an optimal range. It maybe this would happen in a more sub maximal scenario where energy return and energy conservation are more important than maximal force production. I feel that gait is a great example of this. Although maximal force production may also be mitigated by creating too much loading through joint range that is hard to transform.

This then got me thinking about how we train. Many times we are looking for maximal ranges in our training. Maybe we should be looking more at optimal ranges. This may have more implications for sports where we can control the range through skill however. Running is a great example. Controlling stride length will keep us within optimal joint ranges. We must also remember that optimal will be governed by the individual. This will be affected by tissue ability, limb length, speed ability and event. I expect it will be that different events within running e.g. 400 metres will need different joint ranges from a marathon as we balance need for all out power, power-endurance and endurance. Going beyond optimal means our ability to start the next phase of movement, either eccentric to concentric or vice versa, will be compromised. I think that deceleration and acceleration are part of running (unlike the pose method ideology!) However we can mitigate excessive amounts of both having to occur, increasing energy conservation.

If we look at a game of tennis it is much easier to hit a powerful shot when we can manoeuvre our bodies into position. When we are out of position our range of movement may have to be extended to reach the ball. The transformation from eccentric to concentric is sub optimal and affects the power of the shot. The tennis player many times at end range will hit a defensive shot back, aiming to get it in the court rather than a winner! Increases in amortisation from eccentric to concentric reduces cross bridge attachment also decreasing energy return. The closer we get to and stay at end range stretching for the ball the longer we have the amortisation phase reducing the energy gained in the loading motion.

This is a very theoretical piece and mainly my own thoughts (so blame me!!) but it may give us food for thought when we programme ranges/heights for our clients to move through when training.

More may not be better in all circumstances!!!