PURPOSE: The vertical ground reaction force (VGRF) during a countermovement jump (CMJ) is classically described with a single peak force occurring at the low position of the countermovement. However, in practice, jumpers display a variety of CMJ VGRF profiles, including single and double peaks, and jumps where the peak force occurs at, or after, low position. The purpose of this study was to identify the optimal CMJ VGRF profile for maximizing jump height.
METHODS: The top 100 CMJs (based on jump height) from a database of over 2000 jumps, from 211 division one college athletes were analyzed. The 100 athletes (21±3 yr, 96 men) were from several different sports teams (hockey n=33, lacrosse n=25, soccer n=14, basketball n=14, other n=14). All jumps were performed with the hands on the hips. Jumps were categorized as having a single or a double peak in VGRF and whether the peak GRF occurred at, after, or before low position. Jump heights were categorized as above average (1SD>mean), average (within 1SD of mean), or below average (1SD<mean). The association between jump metrics and VGRF profiles was examined using chi square analyses and independent t-tests.
RESULTS: Of the 100 CMJs 22 had a single peak VGRF, of which 14 occurred at low position and 8 occurred after low position. Of the 78 CMJs with a double peak, the 1^st peak was higher in 47 jumps (30 at low position, 13 after low position, 4 before low position), the peaks were equal in 20 jumps (10 at low position, 10 after low position), and the 2^nd peak was higher in 11 (all after low position). Peak GRF occurred at the low point of the countermovement for 82% (14 of 17) of the above average jumps versus 52% (33 of 64) of the average jumps and only 37% (7 of 19) of the below average jumps (P=0.007). For the 78 jumps with two distinct VGRF peaks the 1^st peak was greater than the 2^nd for 77% (10 of 13) of above average jumps, 61% (30 of 49) of average jumps and only 44% (7 of 16) of below average jumps (P=0.033).
CONCLUSIONS: The optimal VGRF profile appeared to be peak force occurring at low position regardless of whether there was a single or double peak. The worst VGRF profile appeared to be jumps with two peaks where the 2nd peak was greater than the 1stpeak, or the 1st and 2nd peaks were equal, but the 1st peak occurred after low position. In conclusion, achieving peak VGRF at the low position of a CMJ appears to be optimal.