ABSTRACT
The deadlift exercise is one of the most effective exercises for developing lower-body strength; however, technique errors can lead to low back injuries. The use of a "walk-in" deadlift machine removes the weight bar by using a lever system with independent handles on either side of the body. Theoretically, this would allow alignment of the load with the center of gravity, encouraging a more upright torso and decreasing the involvement of the low back extensors. This study compared trunk angle, knee angle, and electrical activity of key muscles between the conventional deadlift (CDL) and 2 foot positions (ball of foot or toe alignment) with pronated grip (called BallPro and ToePro) of a walk-in deadlift machine among high-skilled and low-skilled lifters. Although there were no skill group differences, in the combined groups, the walk-in deadlift resulted in a significantly more upright trunk angle (p ≤ 0.05) for both the BallPro (29.9° ± 12.0 SD) and the ToePro (32.4° ± 10.4) compared with the CDL (23.7° ± 11.3) at the start of the lift. Similar results were noted in the midconcentric phase, with trunk angles for the ToePro (46.9° ± 6.8) significantly different from CDL (42.66° ± 3.7), and for the mideccentric phase of the lift, with ToePro (47.2° ± 7.0) significantly higher than CDL (42.9° ± 6.5). ToePro knee angle was significantly more flexed (101.6° ± 10.6) than CDL (110.8° ± 11.5) at the starting position, with both BallPro (135.7° ± 14.2) and ToePro (136.5° ± 8.8) significantly more flexed than CDL (159.3° ± 5.9) in both the midconcentric phase and the mideccentric phase (BallPro 129.2° ± 14.0, ToePro 127.7° ± 8.9, and CDL 150.5° ± 7.8). In the combined low- and high-skilled groups, electrical activity as a percent of maximum isometric root mean square activity of the erector spinae during the BallPro variation (53.1% ± 33.8) was significantly lower than CDL (73.19% ± 23.9), whereas vastus lateralis activity was significantly higher in both BallPro (79.9% ± 26.3) and ToePro (64.3 ± 22.4) compared with CDL (48.6% ± 13.0). Gluteus maximus (GM) activity was significantly lower for BallPro (30.1% ± 16.6) and ToePro (30.2% ± 15.0) than CDL (47.1% ± 27.6). Together, the results indicate that the walk-in deadlift machine has potential to reduce the stress on the low back during the deadlift activity, with subjects generally exhibiting a more upright posture and erector spinae muscle activity, depending on the foot position. However, there was also a shift in muscle activity away from the GM and towards the knee extensors, which may limit the machine's long-term usefulness as a deadlift replacement.
