Identifying Consistent Metrics from the Force-Time Curve of the Countermovement Jump in Combat Fighters and Physically Active Men

We investigated the consistency of metrics obtained from the unweighting, braking, propulsive, and landing phases of the countermovement (CMJ) force-time curve in combat fighters and physically active men. Combat fighters (n=21) and physically actives (n=21) were tested for three days (2-7 days apart). Participants performed four maximal CMJ separated by 1-min for between-day comparisons. From force-time recording, the consistency of 16 CMJ metrics (peak and mean ground reaction forces (GRF), net impulse, and duration from each phase) was investigated using the intraclass correlation coefficient (ICC) and typical error (CV_TE). We considered as "consistent" those metrics showing no systematic differences, ICC ≥ 0.75, and CV_TE ≤ 10%. We further compared the CV_TE between groups and pairs of trials (days). Participants demonstrated more consistency in the braking and propulsive phases, while the unweighting phase did not show any consistent metric. There was no evidence of a learning effect (systematic changes), but analysis appointed more consistency on days 2-3 than on days 1-2 (18 metrics presented lower CV_TE while 11 presented higher). We identified braking and propulsive GRF (peak and mean) and propulsive impulse as consistent metrics for combat fighters, while only propulsive impulse for physically actives. The between-group analyses showed that 24 comparisons favored the combat fighters against only five favoring the physically actives. In conclusion, force-time metrics related to jumping strategy, like phase duration, are less consistent than those related to driven forces and jump output, probably because participants changed their jump strategy during testing days.