Because load theoretically increases as mechanical advantage increases, the addition of chains or elastic bands to conventional barbell squats had been thought to boost the loading during the ascent phase, but no research had confirmed this notion. A study published in the November 2002 issue of the Journal of Strength and Conditioning Research shows that such a modification is essentially pointless.
Researchers from Marquette University assessed the motor unit activation, rate of force development and peak force development of squats done with only a barbell and weight plates; squats done with a barbell, weight plates and chains hung on each end of the barbell; and squats done with a barbell, weight plates and elastic bands. (In the latter two variations, the chains or elastic bands replaced weight plates of the same total load.) The researchers recorded the mean and peak vertical ground reaction forces (GRFs) and the integrated electromyography (I-EMG) for the quadriceps and hamstring muscle groups of the 11 Division I athletes who participated in the study.
Although statistical analysis found significant differences in mean GRF and I-EMG between the eccentric phase and the concentric phase for the three squat variations, it found no differences in GRF and I-EMG among the three variations during either the eccentric phase or the concentric phase. The researchers concluded, “The results question the usefulness of performing squats combining barbell and weight plates with chain and elastic resistance.”