The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0–200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow (“neural drive”) during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 ± 9.8 to 339.0 ± 10.2 N · m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 ± 117 to 2,020 ± 119 ( P < 0.05), 1,802 ± 121 to 2,201 ± 106 ( P < 0.01), 1,543 ± 83 to 1,806 ± 69 ( P < 0.01), and 1,141 ± 45 to 1,363 ± 44 N · m · s⁻¹( P < 0.01), respectively. Corresponding increases were observed in contractile impulse ( P < 0.01–0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased ( P < 0.01–0.05) 22–143% (mean average voltage) and 41–106% (rate of EMG rise) in the early contraction phase (0–200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.

The evaluation of rate of force development during rapid contractions has recently become quite popular for characterising explosive strength of athletes, elderly individuals and patients. The main aims of this narrative review are to describe the neuromuscular determinants of rate of force development and to discuss various methodological considerations inherent to its evaluation for research and clinical purposes. Rate of force development (1) seems to be mainly determined by the capacity to produce maximal voluntary activation in the early phase of an explosive contraction (first 50–75 ms), particularly as a result of increased motor unit discharge rate; (2) can be improved by both explosive-type and heavy-resistance strength training in different subject populations, mainly through an improvement in rapid muscle activation; (3) is quite difficult to evaluate in a valid and reliable way. Therefore, we provide evidence-based practical recommendations for rational quantification of rate of force development in both laboratory and clinical settings.

Combined V-wave and Hoffmann (H) reflex measurements were performed during maximal muscle contraction to examine the neural adaptation mechanisms induced by resistance training. The H-reflex can be used to assess the excitability of spinal α-motoneurons, while also reflecting transmission efficiency (i.e., presynaptic inhibition) in Ia afferent synapses. Furthermore, the V-wave reflects the overall magnitude of efferent motor output from the α-motoneuron pool because of activation from descending central pathways. Fourteen male subjects participated in 14 wk of resistance training that involved heavy weight-lifting exercises for the muscles of the leg. Evoked V-wave, H-reflex, and maximal M-wave (M_max) responses were recorded before and after training in the soleus muscle during maximal isometric ramp contractions. Maximal isometric, concentric, and eccentric muscle strength was measured by use of isokinetic dynamometry. V-wave amplitude increased ∼50% with training ( P < 0.01) from 3.19 ± 0.43 to 4.86 ± 0.43 mV, or from 0.308 ± 0.048 to 0.478 ± 0.034 when expressed relative to M_max (± SE). H-reflex amplitude increased ∼20% ( P < 0.05) from 5.37 ± 0.41 to 6.24 ± 0.49 mV, or from 0.514 ± 0.032 to 0.609 ± 0.025 when normalized to M_max. In contrast, resting H-reflex amplitude remained unchanged with training (0.503 ± 0.059 vs. 0.499 ± 0.063). Likewise, no change occurred in M_max (10.78 ± 0.86 vs. 10.21 ± 0.66 mV). Maximal muscle strength increased 23–30% ( P < 0.05). In conclusion, increases in evoked V-wave and H-reflex responses were observed during maximal muscle contraction after resistance training. Collectively, the present data suggest that the increase in motoneuronal output induced by resistance training may comprise both supraspinal and spinal adaptation mechanisms (i.e., increased central motor drive, elevated motoneuron excitability, reduced presynaptic inhibition).