PT on the Net Research

Repetitive Motion and Biomechanics


Question:

If a client performed 100 push-ups a day for 20 years, would this have a positive or negative impact on the mobility and strength of their shoulder joint?

Answer:

Repetitive movements are performed by us all during our everyday life. However, the movements we are required to perform now are quite different from those we were originally designed to perform several million years ago. What were once natural movements performed in a variety of environments for a number of different reasons, have become more static and repetitive in nature as we have changed from active hunter-gatherers to "office loungers." Over a period of only 100 years we have become inactive; going from active work to sedentary office jobs where the main activity is walking from the house to the car and then to the office. When we are active these days, it’s often only to perform small static movements such as typing, steering and pressing the remote for the TV.

It has been widely reported, in particular by University College London, that repetitive movements are responsible for many of our occupational health issues when it comes to musculoskeletal injuries. Much of this comes from the negative effects of repetitive movement on our soft tissues, including our nerves.

Let’s take a look at some of the effects of repetitive movements. They have a negative effect on joints because, when subjected to prolonged pressure, the cartilage begins to lose its elasticity and become vulnerable to damage (Henderson, Gregory & Swan, 2002). Tendons are visco-elastic and repetitive movements subject them to a mechanical phenomenon known as creep, which means they deform when subjected to prolonged stress (or repetitive movements). Nerves are also visco-elastic, so fast movements are difficult without the proper training, and repetitive movements cause them to resist elongation and so muscles have to go into a protective spasm to reduce the load through them (Cox, 2008). High repetition work can also lead to muscle fatigue and, in some cases, Delayed Onset Muscle Soreness (DOMS) and overuse syndromes. DOMS is associated with an increase in muscle tone and faulty excitation of muscle (Tarnopolsky, 2008). In this state, the muscle is no longer able to contract and relax properly, which means the muscle is in spasm.

There is some evidence to suggest that repetitive movements are not good for us, but exercise is repetitive; so is exercise actually good for us? As always, it depends upon how you do it. If we are to provide our clients with repetitive movements, then we had better make sure they are adequately prepared.

Adaptation is the whole purpose of exercise training. Adaptation requires a systematic application of exercise stress. The stress should be sufficient to stimulate adaptation, but not so severe that breakdown and injury occur (Clark, 2008). Using the principles of overload and specificity, researchers have shown that muscles will adapt to the stresses imposed upon them, but those loads have to be progressive. Progressive overload principles were pioneered by Thomas Delorme, MD, after World War II, and with time these principles allow the body to adapt. Ignoring these principles will likely result in poor results and, more often than not, injury.

So, having explored the background principles to the answer, let’s get back to the initial question. Put simply, if the client understood the principles of progressive overload and sensibly built up to those reps, using a technique that suited the biomechanics of his shoulders, the chances are his body would adapt to the stress and it would have a positive effect on his shoulder mobility and strength. But then there’s more to it isn’t there? A good PT and coach will recognize that working within a training system that develops the whole body as a unit is critical to avoid muscle imbalances.

They will also look to understand the reason for doing 100 push-ups a day and establish whether doing that is effective. Additionally, a biomechanics coach will look to understand the biomechanics of his shoulder; median nerve tension, spasm in Pec Minor, Subscapularis, Infraspinatus (and others). Any issues in these structures will compromise the function of the shoulder joint, and even if the progressive overload principles are adhered to, the muscle imbalances are minimized and the technique is excellent, if the joint is not functioning biomechanically correctly, the risk of injury is increased (Young & Pellett, 1994).

So, to reduce the negative effects of repetitive movements, it’s important to ensure the correct biomechanical function of the individual joints and systems of the body, then progressively work through a combination of training programs that suit the needs of the client. Those needs may include strength and conditioning, functional training, bodybuilding, sports-specific work, Pilates, etc., combined with the relevant cardio work and anything else that helps him achieve his goals. So would doing 100 push-ups per day for 20 years be good for a client? The answer is – only if it’s part of an overall conditioning program and if their biomechanics were suited to performing them.

References

  1. Clark, N. (2008). Protein to build and repair muscles. Nancy Clark’s Sports Nutrition Guidebook. Human Kinetics: Champaign, IL.
  2. Cox, G. (2008). Special needs: The vegetarian athlete. Clinical Sports Nutrition. ed. Burke and Deakin, McGraw-Hill, Sydney, Australia.
  3. Henderson, L., Gregory, J. & Swan, G. (2002). The National Diet and Nutrition Survey: Adults Aged 19 to 64 Years, Vol. 1: Types and Quantities of Foods Consumed. The Stationery Office, London, UK.
  4. Tarnopolsky. (2008). Protein and amino acid needs for training and bulking up. Clinical Sports Nutrition. ed. Burke and Deakin, McGraw-Hill, Sydney, Australia.
  5. Young, V.R. & Pellett P.L. (1994). Plant proteins in relation to human protein and amino acid nutrition, American Journal of Clinical Nutrition, 59: S1203-1212.

Source: Fitpro Network