In contrast, Kohler et al. (2010) compared the triceps muscle activity during seated barbell and
dumbbell shoulder press on a
stable bench or swiss ball reporting that the
stable bench in both conditions produced superior levels of muscle activity
than performing the exercise on a swiss ball.
Training in more
stable environments (i.e. machines rather
than free weights, or barbells rather
than dumbbells) involves greater externally - applied forces.