JC's Musings

Concentric Elastic Benefits

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So, what are the benefits of elastic based resistance (EBR)? As intimated previously, bands are used as a means of overcoming the mechanical disadvantages associated with specific joint angles during free weight resistance (FWR) and increasing the degree of sport specificity.

Let’s have a look at the difference between EBR and FWR in a little more detail in a concentric contraction. The acceleration of any object is proportional to the force being applied and inversely proportional to its mass or inertia (a = f/m). Therefore, using EBR, which has minimal mass (inertia), will allow for greater velocities and accelerations to be produced early in a contraction, compared with FWR movement with an equivalent load. However, it becomes increasingly difficult to maintain high-movement velocities and accelerations towards the end of the concentric phase with EBR, however, the decreases in velocity are less than FWR as you can see in the figure and tables.

How much greater? I looked at this with supine squats way back in 2003 and found significant differences as shown on the figure i.e. shorter contraction times (DOC) and time to peak velocity (TPV), and greater mean (MV) and peak velocities (PV). Of real interest was that time to PV occurred way later during the contraction with EBR compared to FWR (83 vs 57%).

What do you think the implications of this are for force and power, rehab and performance?

Reference: Cronin, J., McNair, P.J., Marshall, R.N. The effects of bungy weight training on muscle function and performance. Journal of Sports Sciences, (2003), 21, 59-71