Another controversial topic when it comes to building muscle is the use of unstable exercises; movements performed where the base of support is unstable would theoretically have the potential to increase muscle activation in an attempt to achieve proper joint and movement stability (Lehman et al. 2006). So in theory, it would seem that unstable training could increase muscle activation due to an increased demand on the neuromuscular system in order to stabilize the articulation joints rendered unstable by the surface used as a base of support. Still in theory that could mean that unstable exercise could improve the capacity of the nervous system to activate certain muscles. Performing a push-up movement with the hands on a swiss ball increases triceps activation significantly compared to a regular push-up (22% activation for stable, 43% for unstable). Changes in pectoral activation were positive with the unstable push-up, but didn't reach statistical significance (21% activation for stable, 26.6% for unstable) this still shows a tendency towards greater activation of the pectorals with this exercise (Lehman et al. 2006). However, when the push ups were performed with the feet on the ball instead of the hands, there was no difference in muscle activation. This would seem to indicate that to increase upper body muscle activation, the unstable surface should be under the hands and not the feet. It would also seem that the closer a muscle is to the source of instability, the more activation potentiation there is while muscles far away from the the source of instability are not affected as much.
However, an argument against the use of unstable movements is that force production during these exercises is lower compared to similar exercises performed on a stable surface (Anderson and Behm, 2001). As we saw earlier, force production is one of the most important factors governing the recruitment of the HTMUs. So it's possible that a technique leading to lesser force production could decrease the efficiency of an exercise.
Unstable training has been widely used for rehabilitation and injury prevention purposes with a considerable amount of success. Naughton et al. (2005) found unstable upper body exercise effective at improving proprioception at the shoulder joint. However, the application of this type of training is not well understood when it comes to mass building purposes. There seems to be two distinct camps in the regard to unstable exercises utilization: those who do almost everything on an unstable surface and those who never use this method. Very few are in the middle and even fewer make a logical utilisation of this technique.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.