Plyometric Exercise Improves Skeletal Muscle Contractile Properties and Jumping Performance in the Aging Population

Background: There is a large body of evidence to suggest that aging, alongside muscle disuse negatively affects neuromuscular system functioning in humans (Aagaard et al., 2010). Different resistance training (RT) strategies are commonly prescribed as a viable tool to counter the above-mentioned age-related degenerative changes in muscle function. The underlying, widely accepted assumption is that the classical RT would lead to a greater muscle power output and consequently lower the risk of frailty in elderly. However, there has been a growing debate in the literature regarding the insufficient intensity of classical RT in efficiently preventing age-related atrophy and muscle fiber loss. Recently, Zubac and Šimunič (2017) showed that 8-week plyometric training (PT) in the adult population increased lower-limb explosive power for 12.2%, decreased tensiomyography (TMG) derived skeletal muscle contraction time in four (out of five) lower-limb muscles, 8.2% decrease in vastus lateralis MHC-1.

Aim: We tested the hypothesis whether PT can be used as a means to enhance muscle power output and contractile velocity (contraction time) in elderly.

Methods: All data were collected before and after an 8-week PT (3 weekly sessions), with one-week rest after the fourth week of training. Using noninvasive TMG we assessed contraction time (Tc) and the maximal amplitude of radial displacement (Dm) in 23 participants (66.7±5.2 years), randomly allocated in the PLYO group (n=11) or control group (n=12). TMG was measured in five lower-limb muscles of the dominant leg: vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), gastrocnemius medialis (GM) and lateralis (GL). The electro-mechanical efficiency (EME) of the GM was evaluated and calculated as a ratio between Dm and peak-to-peak M-wave amplitude (Paravlic et al., 2017). In addition, we measured muscle power output improvement via counter movement jump (C_MJ) and take-off velocity (V_V) on a ground force plate.

Results: C_MJ height and V_V increased by 14.2% and 8.2% only in the PLYO group (p=0.01). Tc decreased in the BF (-5.9%; p=0.028), GM (-9.6%; p=0.075). In the GL a non-significant decrease in Tc was observed (-28.9%, p=0.858), and there were no changes in Tc of the VL (p=0.233) and TA (p=0.360), and estimated VL MHC-1 proportion after PT (p=0.579). Dm decreased only in BF (-20.8%; p=0.031), while the EME index of the GM muscle improved by 23% (p=0.095).

Discussion and Conclusions: The present study supports the benefits of high-velocity PT training for improving explosive effort in the aged population. Lower limb explosive power, muscle contractility mechanics and EME efficiency markedly improved in response to PT. This bears strong implications in terms of quality of life improvements throughout aging. The present findings may aid to develop countermeasures to attenuate the effects of aging on muscle function by designing novel exercise interventions for the elderly.