The influence of patellar tendon and muscle-tendon unit stiffness on quadriceps explosive strength in man

The influence of musculotendinous tissue stiffness on contractile rate of torque development (RTD) remains opaque. This study examined the relationships between both patellar tendon (PT) and vastus lateralis (VL) muscle-tendon unit (MTU) stiffness, and voluntary and evoked knee extension RTD. Fifty-two healthy untrained males completed duplicate laboratory sessions. Absolute and relative RTD was measured at 50 Nm/25%MVT increments from onset and sequentially during explosive voluntary and evoked octet (supramaximal stimulation: [8 pulses at 300 Hz]) isometric contractions. Isometric maximum voluntary torque (MVT) was also assessed. PT and MTU stiffness were derived from simultaneous force and ultrasound recordings of the PT and VL aponeurosis during constant RTD ramp contractions. Absolute and relative (to MVT and resting tissue length) stiffness (k) was measured over identical torque increments as RTD. Pearson's correlations tested relationships between stiffness and RTD measurements over matching absolute/relative torque increments. Absolute and relative PT k was unrelated to equivalent voluntary or evoked RTD (r = 0.020.255, P = 0.069-0.891). Absolute MTU k was unrelated to voluntary or evoked RTD (r ≤ 0.191, P ≥ 0.184), however some measures of relative MTU k were related to relative voluntary/evoked RTD (e.g. RTD25-50%MVT r = 0.374/0.353, P = 0.007/0.014). In conclusion, relative MTU k explained a small proportion of the variance in relative voluntary and evoked RTD (both ≤19%), despite no association of absolute MTU k or absolute/relative PT k with equivalent RTD measures. Therefore the muscle-aponeurosis component, but not free tendon was associated with relative RTD, although it seems an overriding influence of MVT negated any relationship of absolute MTU k and absolute RTD. This article is protected by copyright. All rights reserved.