Altered countermovement jump force profile and muscle-tendon unit kinematics following combined ballistic training

Abstract

Combined heavy- and light-load ballistic training is often employed in high-performance sport to improve athletic performance and is accompanied by adaptations in muscle architecture. However, little is known about how training affects muscle-tendon unit (MTU) kinematics during the execution of a sport-specific skill (e.g., jumping), which could improve our understanding of how training improves athletic performance. The aim of this study was to investigate vastus lateralis (VL) MTU kinematics during a countermovement jump (CMJ) following combined ballistic training. Eighteen young, healthy males completed a 10-week program consisting of weightlifting derivatives, plyometrics, and ballistic tasks under a range of loads. Ultrasonography of VL and force plate measurements during a CMJ were taken at baseline, mid-test, and post-test. The training program improved CMJ height by 11 ± 13%. During the CMJ, VL's MTU and series elastic element (SEE) length changes and velocities increased from baseline to post-test, but VL's fascicle length change and velocity did not significantly change. It is speculated that altered lower limb coordination and increased force output of the lower limb muscles during the CMJ allowed more energy to be stored within VL's SEE. This may have contributed to enhanced VL MTU work during the propulsion phase and an improved CMJ performance following combined ballistic training.

Keywords: Ultrasonography; muscle mechanics; performance; resistance exercise; weightlifting.

FIGURE 1

(A) Individual vertical jump heights (open circles, n = 18) and B) mean paired differences (point estimate ±95% confidence interval [CI]) between countermovement jumps performed at baseline, mid‐test (Mid), and post‐test (Post) of the 10‐week combined ballistic training program. Solid lines link the same participant. * and a 95% CI that does not cross zero indicates a significant difference between baseline and post‐test (p = 0.011), whereas “ns” and an overlapping 95% CI with zero indicates no significant difference between baseline and mid‐test (p = 0.442) and mid‐test and post‐test (p = 0.066). Tukey post hoc comparisons controlled the family‐wise error rate at 5% and were computed with individual variances.

FIGURE 2

Mean (solid lines) ± standard deviation (shaded areas with dotted lines) vertical ground reaction force during the countermovement jumps (CMJs) performed at baseline (black), mid‐test (red), and post‐test (blue) of the 10‐week ballistic training program. As the duration of the CMJ varied between participants, group traces were constructed by time normalizing the data to 100 points using linear interpolation over a period corresponding to 20 frames before the initiation of the countermovement (0%) to take‐off (100%). Vertical lines (left to right) represent the start of the unloading, braking, and propulsion phases, respectively.

FIGURE 3

Mean (solid lines) ± standard deviation (shaded areas with dotted lines) vastus lateralis (TOP) muscle‐tendon unit (MTU), (MIDDLE) series elastic element (SEE), and (BOTTOM) vastus lateralis fascicle lengths during the countermovement jumps (CMJs) performed at baseline (black), mid‐test (red), and post‐test (blue) of the 10‐week ballistic training program. As the duration of the CMJ varied between participants, group traces were constructed by time normalizing the data to 100 points using linear interpolation over a period corresponding to 20 frames before the initiation of the countermovement (0%) to take‐off (100%). Vertical lines (left to right) represent the start of the unloading, braking, and propulsion phases, respectively.

FIGURE 4

Mean paired differences (point estimate ±95% confidence interval [CI]) in vastus lateralis' (A) muscle‐tendon unit (MTU), (B) series elastic element (SEE), and (C) fascicle length changes between unloading, braking, and propulsion phases during countermovement jumps performed at baseline, mid‐test (Mid), and post‐test (Post) of the 10‐week combined ballistic training program. As the propulsion phase specifically resulted in shortening (i.e., a negative length change), negative differences indicate more shortening in the first listed testing session, whereas negative differences in the unloading and braking phases indicate less lengthening. A 95% CI that does not cross zero indicates a significant difference between testing sessions, and descriptive results are reported in the text. Tukey post hoc comparisons controlled the family‐wise error rate at 5% and were computed with individual variances.

FIGURE 5

Mean paired differences (point estimate ±95% confidence interval [CI]) in vastus lateralis' (A) muscle‐tendon unit (MTU), (B) series elastic element (SEE), and (C) fascicle velocity changes between unloading, braking, and propulsion phases during countermovement jumps performed at baseline, mid‐test (Mid), and post‐test (Post) of the 10‐week combined ballistic training program. As the propulsion phase specifically resulted in shortening (i.e., a negative velocity), negative differences indicate a higher shortening velocities in the first listed testing session, whereas negative differences in the unloading and braking phases indicate lower lengthening velocities. A 95% CI that does not cross zero indicates a significant difference between testing sessions, and descriptive results are reported in the text. Tukey post hoc comparisons controlled the family‐wise error rate at 5% and were computed with individual variances.