This research aimed to assess differences and relationships between variables using conventional FVP with SB and TB, and to explore relationships between FVP variables and those from body weight jumps. Our results showed that, compared to SB, participants could generate greater force, velocity, and power with TB, while individualized FVP assessed strength characteristics as “force-dominant”. Moreover, FVimb evaluated by both TB and SB was significantly correlated, whereas only Sfv and CMJ/SJ in the TB condition were correlated with the body weight jump. Thus, FVP calculated by TB can be used as an alternative to that calculated by SB, although ESD calculated by body weight jump height may be partly used as a potential alternative to FVP.
The CV of jump height for both the SB and TB conditions ranged from 1.47–3.86%. For the ICC and weighted kappa coefficients between the two conditions of the unloaded jump, the ICCs for SJ and CMJ w/o AS were 0.968 and 0.945, respectively, and the kappa coefficient for CMJ w/o AS was 0.580. No differences were observed in the jump height or jump height ratio between the two conditions, and the unloaded and loaded jumps were considered reliable.
Jump height, mean velocity, and mean power values with 40%, 60%, and 80%+BW were significantly higher in the TB condition than in the SB condition. The mean force with 60% and 80%+BW were also significantly greater (Fig. 1c). Previous research by Camara et al. reported that deadlift exercise using a TB produced greater peak ground reaction force, power, and velocity than conventional deadlift using an SB at 65% and 85% repetition maxima (2). Suchomel et al. and Swinton et al. demonstrated similar results to our study(19, 20). Suchomel et al. reported that the hexagonal barbell jump produced greater peak power and peak velocity at peak power than the SB jump squat across loads (19). Swinton et al. reported that the hexagonal barbell jump produced a greater peak ground reaction force, peak velocity, and rate of force development than jump squats with SB bell in various load regimes(20). Swinton et al. explained these results as follows: the change in position of the external resistance from the shoulders to a closer location to the body's center of mass may have reduced the shear force and torque applied to the lumbar region and moved the torso independently (20). These attributes can be used to reproduce the unloaded jump technique. A review of the video footage revealed that the amount of forward lean of the trunk was similar to that of the unloaded jump (20). Thus, the load position and joint kinematics between the conditions can affect the kinetic variables.
Our results showed different theoretical values for the SB and TB conditions. F0 (theoretical maximum force) was significantly higher in the TB condition than in the SB condition, and V0 was significantly higher in the SB condition than in the TB condition. As Sfv is the slope of the straight line connecting F0 and V0 (i.e., the force-velocity linear relationship), it showed a significant between-condition. Furthermore, FVimb under TB condition was larger than that under SB condition because FVimb is calculated as the ratio between the calculated Sfv and theoretical Sfvopt. The Sfv and FVimb values calculated under TB conditions showed a more force-dominant FVP than those calculated under SB conditions. This is supported by previous studies(19, 20) and the present study, which showed that vertical jumps performed with a TB (hexagonal bar) resulted in higher jump heights and greater force production capacities than vertical jumps performed using an SB bell (19, 20). However, the relative reliability between the two conditions of body weight jump (Unloaded SJ) was ensured, and no differences were observed between the conditions or any variable, including jump height. Therefore, it should be noted that the use of a TB would result in a force-dominant FVP but not because of a lower jump ability.
The Pmax for the FVP variable was not significantly different between the conditions. This suggests that TB and SB can be used interchangeably to assess overall neuromuscular function. Furthermore, the FVimb values for both the conditions had a significant positive correlation. The application of FVP using TB could be an alternative method to SB for evaluating whole neuromuscular function and strength characteristics, although the tendency to assess force dominance must be considered. Alternative methods to traditional FVP calculations have several considerations. Notably, the calculated FVP may differ if different motor tasks are performed. Nishioka and Okada showed that the FVP variables in SJ and CMJ may be incompatible (14). Moreover, Samozino et al.'s equation was not formulated using a movement task such as a vertical jump, which considered redundancy and coordination (17, 18). Our proposal for the use of FVP is based on an understanding of these characteristics.
No significant correlation was observed between the CMJ/SJ in the SB and TB conditions. This suggests that body weight jump cannot be used as an alternative method to FVP calculated from loaded jump height. In a cross-sectional study examining jump data from different sporting events, the CMJ/SJ jump height ratio (known as the eccentric utilization ratio) ranged 4.00–18.63%(10). Another study reported that the eccentric utilization ratio was 1.02–1.17(12). Furthermore, smaller CMJ/SJ ratios have improved in recent years(15, 21). The lack of consensus on appropriate values for CMJ/SJ makes it challenging to set a threshold for CMJ/SJ to replace FVP. Therefore, it is necessary to consider other validated methods. Sfv and CMJ/SJ showed a significant positive correlation under TB conditions. This result can be interpreted as V0 increasing with increasing CMJ height relative to SJ (velocity-dominant). This may be partly because the TB jump has kinematics similar to those of the body-weighted jump. However, it does not indicate whether Sfv and CMJ/SJ deviate from the optimal threshold values. Our findings may provide a simple approach for determining the existence of a force or velocity deficit. However, they do not provide a threshold for identifying the FVP characteristics with the use of CMJ/SJ.
This study has several limitations. First, athletes were not recruited. Students are more likely to have a velocity-dominant profile(8), while athletes have different profiles for different sporting events(8) that also depend on their respective positions in team sports (1). Second, this study did not focus on women. Sex differences may influence this profile(8) and require further study.