3 research outputs found
The influence of training and athletic performance on the neural and mechanical determinants of muscular rate of force development
Neuromuscular explosive strength (defined as rate of force development; RFD) is
considered important during explosive functional human movements; however this
association has been poorly documented. It is also unclear how different variants of
strength training may influence RFD and its neuromuscular determinants. Furthermore,
RFD has typically been measured in isometric situations, but how it is influenced by the
types of contraction (isometric, concentric, eccentric) is unknown. This thesis compared
neuromuscular function in explosive power athletes (athletes) and untrained controls,
and assessed the relationship between RFD in isometric squats with sprint and jump
performance. The athletes achieved a greater RFD normalised to maximum strength
(+74%) during the initial phase of explosive contractions, due to greater agonist
activation (+71%) in this time. Furthermore, there were strong correlations (r2 = 0.39)
between normalised RFD in the initial phase of explosive squats and sprint
performance, and between later phase absolute explosive force and jump height (r2 =
0.37), confirming an association between explosive athletic performance and RFD. This
thesis also assessed the differential effects of short-term (4 weeks) training for
maximum vs. explosive strength, and whilst the former increased maximum strength
(+20%) it had no effect on RFD. In contrast explosive strength training improved
explosive force production over short (first 50 ms; +70%) and long (>50 ms; +15%)
time periods, due to improved agonist activation (+65%) and maximum strength
(+11%), respectively. Explosive strength training therefore appears to have greater
functional benefits than maximum strength training. Finally, the influence of
contraction type on RFD was assessed, and the results provided unique evidence that
explosive concentric contractions are 60% more effective at utilising the available force
capacity of the muscle, that was explained by superior agonist activation. This work
provides a comprehensive analysis of the association between athletic performance and
RFD, the differential effects of maximum vs. explosive strength training, and the
influence of contraction type on the capacity for RFD
Neuromuscular performance of explosive power athletes versus untrained individuals
Electromechanical delay (EMD) and rate of force development (RFD) are determinants
of explosive neuromuscular performance. We may expect a contrast in EMD and RFD between
explosive power athletes, who have a demonstrable ability for explosive contractions, and
untrained individuals. However, this comparison, and the neuromuscular mechanisms for any
differences, has not been studied. The neuromuscular performance of explosive power
athletes (n = 9) and untrained controls (n = 10) was assessed during a series of twitch, tetanic,
explosive and maximum voluntary, isometric knee extensions. Knee extension force and EMG of
the superficial quadriceps was measured in three 50 ms time windows from their onset, and
normalised to strength and maximal M-wave (Mmax), respectively. Involuntary and voluntary EMD
were determined from twitch and explosive voluntary contractions, respectively, and were similar
for both groups. The athletes were 28% stronger and their absolute RFD in the first 50 ms
was 2-fold that of controls. Athletes had greater normalised RFD (4.86 ± 1.46 vs. 2.81 ± 1.20
MVC.s-1) and neural activation (mean quadriceps, 0.26 ± 0.07 vs. 0.15 ± 0.06 Mmax) during the
first 50 ms of explosive voluntary contractions. Surprisingly the controls had a greater normalised
RFD in the second 50 ms (6.68 ± 0.92 vs. 7.93 ± 1.11 MVC.s-1) and a greater change in EMG
preceding this period. However, there were no differences in the twitch response or normalised
tetanic RFD between groups. The differences in voluntary normalised RFD between
athletes and controls were explained by agonist muscle neural activation, and not the similar
intrinsic contractile properties of the groups
Tendinous tissue adaptation to explosive- vs. sustained-contraction strength training
© 2018 Massey, Balshaw, Maden-Wilkinson, Tillin and Folland. The effect of different strength training regimes, and in particular training utilizing brief explosive contractions, on tendinous tissue properties is poorly understood. This study compared the efficacy of 12 weeks of knee extensor explosive-contraction (ECT; n = 14) vs. sustained-contraction (SCT; n = 15) strength training vs. a non-training control (n = 13) to induce changes in patellar tendon and knee extensor tendon-aponeurosis stiffness and size (patellar tendon, vastus-lateralis aponeurosis, quadriceps femoris muscle) in healthy young men. Training involved 40 isometric knee extension contractions (three times/week): gradually increasing to 75% of maximum voluntary torque (MVT) before holding for 3 s (SCT), or briefly contracting as fast as possible to ~80% MVT (ECT). Changes in patellar tendon stiffness and Young's modulus, tendon-aponeurosis complex stiffness, as well as quadriceps femoris muscle volume, vastus-lateralis aponeurosis area and patellar tendon cross-sectional area were quantified with ultrasonography, dynamometry, and magnetic resonance imaging. ECT and SCT similarly increased patellar tendon stiffness (20% vs. 16%, both p < 0.05 vs. control) and Young's modulus (22% vs. 16%, both p < 0.05 vs. control). Tendon-aponeurosis complex high-force stiffness increased only after SCT (21%; p < 0.02), while ECT resulted in greater overall elongation of the tendon-aponeurosis complex. Quadriceps muscle volume only increased after sustained-contraction training (8%; p = 0.001), with unclear effects of strength training on aponeurosis area. The changes in patellar tendon cross-sectional area after strength training were not appreciably different to control. Our results suggest brief high force muscle contractions can induce increased free tendon stiffness, though SCT is needed to increase tendon-aponeurosis complex stiffness and muscle hypertrophy