We introduced KB’s a while back, indicating their effectiveness in non-specific (pre-season / general prep phase) aerobic conditioning. Similarly, when we talked about KB training and spinal loading, we mentioned that the KB swing compliments the squat by providing a balance to the spinal loading pattern as well as activating the spinal extensors and gluteal muscles at 50% and 80% of their respective MVC. Therefore kettlebells have a role to play in muscular endurance & strength training.

For kettlebell advocates, a niche electrophysiology research is starting to validate kettlebell training paralleling anecdotal evidence for the past 50 years that the method works.

The latest study advocating KB training comes from The British Journal of Sports Medicine. They examined 14 different leg flexion and balance/coordination exercises and found that KB swings specifically target the semitendinosus muscle (medial hamstring muscle) significantly more then the biceps femoris (lateral hamstring muscle). In fact, the activation level between both muscles during the KB swing were significantly different (p<0.05). In contrast, lying leg curls significantly activated the biceps femoris muscle to a greater degree than the semitendinosus (p<0.05).

Physiologically, the semitendinosus muscle undergoes both eccentric loading upon ground contact & high-velocity concentric contraction following mid-flight in sprinting. Owing to its’ physiology, the semitendinosus is likely to fatigue quickly during sprinting activities.

Research implications

Adding kettlebell swings to a strength training routine will specifically and eccentrically load the semitendinosus, leading to a greater specific strength in the muscle.