Abstract
PurposeTo investigate the time-course of changes in knee-extensors muscle mass, architecture and function in response to plyometric training (PLT) performed on a novel training device, the Tramp-Trainer. This machine consists in a trampoline connected to an inclined sledge which allows the performance of repeated jumps while the subject is sitting on a chair.MethodsEight healthy males (173.6 ± 4.7 cm, 69.7 ± 13.5 kg, 25.3 ± 4.6 years) underwent 6 weeks of bilateral PLT on the tramp-trainer machine. Training was performed three times per week (between 120 and 150 bounces per session). Knee-extensor maximum voluntary torque (MVT) and power, quadriceps femoris (QF) volume (VOL), cross-sectional area from the 20% to the 60% of femur length and CSAmean, together with vastus lateralis (VL) architecture (fascicle length, Lf, and pennation angle, PA) were assessed after 2, 4, and 6 weeks of PLT.ResultsAll results are presented as changes versus baseline values. MVT increased by 17.8% (week 2, p < 0.001) and 22.2% (week 4, p < 0.01), respectively, and declined to 13.3% (p < 0.05) at week 6 of PLT. Power increased by 18.2% (week 4, p < 0.05) and 19.7% (week 6, p < 0.05). QF VOL increased by 4.7% (week 4, p < 0.05) and 5.8% (week 6, p < 0.01); VL VOL increased by 5.2%, (p < 0.05), 8.2%, (p < 0.01), and 9.6% (p < 0.05) at weeks 2, 4, and 6, respectively. An increase in Lf was detected already at wk 2 (2.2%, p < 0.05), with further increase at 4 and 6 weeks of PLT (4 and 4.4%, respectively, p < 0.01). PA increased by 5.8% (p < 0.05) at week 6. Significant positive correlations were found between CSAmean and Power (R2 = 0.46, p < 0.001) and between QF VOL and Power (R2 = 0.44, p < 0.024).ConclusionsPLT induced rapid increases in muscle volume, fascicle length, pennation angle, torque and power in healthy younger adults. Notably, changes in VL VOL and Lf were detectable already after 2 weeks, followed by increases in knee extensors VOL and power from week 4 of PLT. Since the increase in CSAmean and QF VOL cannot fully explain the increment in muscle power, it is likely that other factors (such as adaptations in neural drive or tendon mechanical properties) may have contributed to such fucntional changes.
Highlights
Muscle power is a major contributor of performance both in sports and in daily life activities, and several studies have been carried out in order to understand how power could be improved in young, older, and clinical populations (Harries et al, 2012; Cook et al, 2013; Reid et al, 2015)
The average values for functional and morphological adaptations at each time point are presented in Tables 1, 2, while the percentage changes of the same parameters during the time-course -compared to baseline- are shown in Figures 3, 4
Mean maximum voluntary contraction torque (MVT) values increased by 17.8 ± 7.4% (p < 0.001) after only 2 weeks of plyometric training (PLT)
Summary
Muscle power is a major contributor of performance both in sports and in daily life activities, and several studies have been carried out in order to understand how power could be improved in young, older, and clinical populations (Harries et al, 2012; Cook et al, 2013; Reid et al, 2015). In this regard, plyometric exercise has been shown to be effective for improving muscular performance both in young athletes (Ramìrez-Campillo et al, 2014) and recreationally active people (Makaruk et al, 2011). The contributing factors to such increases can be found in (i) muscle morphological adaptations (i.e., architectural, whole muscle and muscle fibers size changes) (Pottiger Jeffrey et al, 1999; Blazevich et al, 2003; Malisoux et al, 2006b; McKinlay et al, 2012), (ii) tendon and joint stiffness properties (Hirayama et al, 2017), and (iii) modifications of neural activation (Behrens et al, 2014, 2016; Hirayama et al, 2017)
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