(12) COMPARISON OF FORCE-TIME CHARACTERISTICS OF LOADED COUNTERMOVEMENT JUMPS USING WEIGHT-MATCHED RIGID AND FLEXIBLE BARBELLS

Purpose:

Loaded countermovement jumps (LCMJs) are frequently used as a tool to improve the triple extension abilities of strength/power athletes. Commonly, rigid barbells are chosen to overload the stretch-shortening cycle, however, anecdotal evidence has emerged suggesting that the use of weight-matched flexible barbells (Tsunami Bar L3, West Columbia, USA) could influence key phase characteristics of the LCMJ, further enhancing training effectiveness. 

Methods:  

Twelve NCAA Division I, male athletes performed 3 LCMJs with weight-matched rigid and flexible barbells. Force-time data were captured through the use of in-ground force plates recording at 1000hz (Kistler, Winterthur, Switzerland). A counterbalanced design resulted in two days of testing where athletes repeated the protocol using the opposing barbell 48 hours later. Each athlete was motivated to exert maximal effort being cued to ‘jump as high and as fast as you can.’ 

Results:  

Data were normalized to participant body mass prior to analysis. Data for each condition were then evaluated using a paired t-test with a confidence level of 0.95. Overall, 71 of 108 variables displayed a significant difference between conditions (α = 0.05). A selection of phase-specific variables are displayed in Table 1 below. 

Conclusions and Practical Applications: 

Jumping with a rigid barbell can be seen to elicit a, longer, slower and deeper eccentric phase with reduced force at the onset of the concentric phase (force at zero velocity). While the impulse-driven outcome variable of jump height was no different between conditions, spatiotemporal variables reveal that the time to achieve jump height (contraction time) and countermovement depth were significantly shorter with the flexible barbell (Table 1 below).

Interestingly, impulse derived in the first 50% of the concentric phase (P1 concentric impulse) was accentuated under the flexible condition. Thereafter, P2 concentric impulse was much reduced, potentially owing to the upward recoil of mass, the increased movement velocity and the lower affordance of the athlete to push forcefully into the ground. This ‘forceful to fast’ signature may have greater dynamic correspondence with the range of motion, magnitude and direction of movement commonly displayed during sporting actions that require explosive braking and redirection of the center of mass.

Despite these results pointing toward favorable force-time characteristics using this novel approach, further research is necessary to determine whether long-term implementation of this method would result in greater, generalizable training outcomes than when compared to a traditional approach using a rigid barbell. 

Acknowledgements: None