Sprinting is one of the fastest events in the Olympic Games, the world record for the 100 m sprint is 9.58 s created in 2009 (Haugen et al., 2019; Kawama et al., 2024). The sprinters need to start rapidly and accelerate to maximal velocity (Donaldson et al., 2022). Acceleration is one of the main phases in the 100 m or 200 m race, which is critical to increasing maximal horizontal velocity and sprint performance (Healy et al., 2022; Nagahara et al., 2014). A 30-m (30 m) sprint test is a classical method of assessing acceleration, which requires sprinters to accelerate rapidly from zero to a high horizontal velocity, with a strong correlation with 100 m performances (Bezodis et al., 2015; Bezodis et al., 2019; van den Tillaar et al., 2023). The best sprinters have a higher level of acceleration and require a high level of lower limb explosive strength (Slawinski et al., 2017).

Lower limb explosive strength refers to sprinters’ ability to generate maximum force in a very short time, helping them achieve good acceleration (Samozino et al., 2022; Watanabe, 2018). Studies have demonstrated that elite sprinters have greater lower limb explosive strength, with a higher rate of force development (RFD) than sub-elite sprinters (Crotty et al., 2024; Slawinski et al., 2010). Lower limb explosive strength is regulated by the central nervous system, where neural impulses are transmitted through nerve fibers to the anterior horn α-motor neurons of the spinal cord. This process excites α-motor neurons, rapidly recruiting their associated muscle fibers for explosive contraction. Therefore, it is speculated that lower limb explosive strength is affected by neural factors and muscular factors, such as rapid recruitment speed of α-motor neurons, high motor unit discharge rates, and fast muscle fiber contractions (Dideriksen et al., 2020; Del, 2023). A study found that RFD increased after 4 weeks of strength training can be attributed to the enhanced recruitment speed of α-motor neurons (Del et al., 2022).

Previous studies have predominantly used reaction time to assess the neural function of sprinters (Tonnessen et al., 2013). However, the neural function of sprinters can be explored using more detailed methods. H reflex and M wave were the effective and non-invasive methods to reflect the spinal neural function, induced by electrically stimulating the peripheral nerve (mixed nerve), founded by German physiologist Paul Hoffmann in 1918 (Magladery and Mcdougal, 1950). The reflex arc of the H-reflex is similar to the muscle stretch reflex. H reflex was evoked by the electrical stimulation of Ia afferent nerves (bypassing the muscle spindle), which activates spinal motor neurons and recruits motor units, resulting in muscle contraction (Wolpaw, 2010). M wave was the compound muscle action potential, indicating the direct response of the muscle to electrical stimulation of the motor nerve (bypassing the reflex pathway) in H reflex tests (McNeil et al., 2013). The action potentials of the H reflex and M wave can be recorded via surface electromyography (EMG). Therefore, H-reflex and M wave were used to assess the excitability of the spinal α-motor neurons and the synaptic transmission efficiency of the Ia afferent, which also reflected the plasticity of the spinal cord (Aagaard et al., 2002; Theodosiadou et al., 2023). In recent studies, the H reflex was widely to assess spinal cord function across various populations, such as patients with spinal cord injury, healthy people, and athletes (Guan and Koceja, 2011; Raffalt et al., 2015; Sun et al., 2022; Vila-Chã et al., 2012).

Animal experiments identified that the plasticity of the spinal cord is primarily trained through the corticospinal tract (de Leon et al., 1998). The spinal cord is the final common pathway of the motor pathway, receiving sensory and motor signals from the central and peripheral nervous systems. V wave is an electrophysiological variant of the H-reflex, which reflects the excitability of descending corticospinal pathways, and the supraspinal input to the spinal motoneuron pool (Aagaard et al., 2002). H reflex and M wave were evoked by submaximal electrical stimulation of the peripheral nerves in rest, and V wave was evoked by supramaximal electrical stimulation of the peripheral nerves during maximal voluntary contractions (MVC) (McNeil et al., 2013). V wave was the action potentials recorded after orthodromic impulses from descending voluntary drive collided with antidromic impulses evoked by supramaximal stimulation of motor axons. Studies have shown that strength-trained athletes have lower H-reflex excitability thresholds and higher V-wave responses than untrained individuals (Grosprêtre et al., 2018; Tøien et al., 2023; Vila-Chã et al., 2012). Changes in the H-reflex and V-wave were observed after resistance training, accompanied by enhanced sports performance (Aagaard, 2018; Holtermann et al., 2007; Kinnunen et al., 2019a).

Muscle-tendon function is fundamental to the development of lower limb explosive strength in sprinters (Cavedon et al., 2023). One hundred-meter (100 m) sprinters with more lean body mass and strength significantly have better sprint performance (Barbieri et al., 2017). The biomechanics data from a full-body musculoskeletal model for predicting sprint performance showed that sprint was most sensitive to changes in muscle (Lin and Pandy, 2022). An investigation revealed that the muscle group sprint coaches considered to be the most important for enhancing lower limb explosive strength are quadriceps, hamstrings and gastrocnemius (Healy et al., 2021). Sprint mechanical parameters changed after 5 months of training in national-level sprinters, accompanied by increments of muscle volumes in the lower limb (Nuell et al., 2020). Tendon also plays an important role in sprint, the ankle and plantar flexor muscle-tendon units rapidly apply force to the ground by storing and releasing elastic energy, shortening the contact time to maintain high velocity (Crotty et al., 2024; Yamazaki et al., 2022). Sprinters are characterized by higher active tendon stiffness during high-speed movements after training (Kubo et al., 2020).

Most studies have researched the effects of neural and muscular factors on lower limb explosive strength in sprinters, but determining which factor plays a more critical role still requires further investigation. In addition, studies investigating neural function in sprinters through H-reflex and V-wave analysis are relatively limited. Thus, this study aimed to explore the key neuromuscular factors predicting lower limb explosive strength, focus on assessing the neural function from spinal and supraspinal in sprinters through the H reflex and V-wave, and hypothesized that neural factors have a greater influence on lower-limb explosive strength.

The descriptive values of the H-reflex and V-wave, skeletal muscle function, and lower limb explosive strength are shown in Table 1.

Table 2 shows the correlation between the H-reflex and V-wave, skeletal muscle function, and lower limb explosive strength. 30 m sprint time significantly positively correlated with Achilles tendon stiffness (r = 0.50, p = 0.05, 95%CI: 0.01–0.81). H-index (r = −0.54, p = 0.04, 95%CI: 0.82 to −0.03), V/MmaxA (r = −0.59, p = 0.02, 95%CI: 0.85 to −0.11), and HECC60 (r = −0.53, p = 0.04, 95%CI: 0.82 to −0.03) showed significant negative correlations with 30 m sprint time, indicating that higher values of these indicators are associated with shorter 30 m sprint time. There was no significant correlation between the 30 m sprint time and concentric isokinetic knee flexion and extension (p > 0.05). RFD had a significant positive correlation with Hmax/Mmax (r = 0.57, p = 0.03, 95%CI:0.08–0.84) and QECC60 (r = 0.53, p = 0.04, 95%CI: 0.02–0.82).

Table 3 shows the results of the stepwise multiple regression analysis of predictors determining 30 m sprint time. V/MmaxA and HECC60 were identified as predictors of 30 m sprint time, and the R ² explained 57.5% of the variance. The multivariate formula was: 30 m sprint time = 4.713–0.448*V/MmaxA −0.264*HECC60. Vertical stiffness and QECC60 explained 82.7% of the variation in RFD.

The primary findings of this study indicated that V/MmaxA and HECC were predictive factors of 30 m sprint time and vertical stiffness and QECC was the predictive factor of RFD. Consistent with this study’s hypothesis, neural factors have a greater impact on lower limb explosive strength, V/MmaxA, Hmax/Mmax, and NCV were significantly correlated with 30 m sprint time and RFD.

Sprinters need to react rapidly and accelerate to a high horizontal speed from a stationary position after receiving an external order, which requires a high-level neuromuscular function ability (Bezodis et al., 2019). 30 m test is commonly used to assess acceleration and lower limb explosive strength, and this study found that neural and muscular factors were both associated with 30 m sprint time (Healy et al., 2022; Samozino et al., 2022). Recent studies have revealed that lower limb explosive strength is determined by the ability of the neural drive to the muscle, especially driven by the cortex (Del et al., 2019; Grospretre et al., 2018). Rapid contractions of muscles depend on motor units that are highly synchronized to activate and a high initial discharge rate at the onset of activation (Maffiuletti et al., 2016; Del, 2023). V-wave was considered an indicator evaluating the neural drive in descending corticospinal pathways, reflecting the change of motoneuron excitability and neural adaptation to training (Aagaard et al., 2002; Nevanpera et al., 2023; Tomazin et al., 2022). This study found that the V-wave was a key determinant of 30 m, demonstrating that a large magnitude of descending central drive from supraspinal centers may enhance sprint performance. Similar results have also been observed in female ice hockey players: V-wave amplitude increased significantly, accompanied by an increase in plantarflexion MVC force and RFD after around 2 weeks of HIIT training (Kinnunen et al., 2019b). Meanwhile, the results showed no significant correlation between the H-reflex and 30 m in sprinters. Compared to endurance athletes, a lower H-reflex was observed in sprinters (Maffiuletti et al., 2001; Ozmerdivenli et al., 2002; Tøien et al., 2023). After short-term endurance and strength training, V/MmaxA significantly increased in the strength group, with no changes in the endurance group, and H/M displayed reverse trends (Vila-Chã et al., 2012). This indicates that changes following training in the strength group depend on the increased descending neural drive instead of spinal α-motoneuron excitability, leading to increased MVC. Strength-trained athletes demonstrated a larger V-wave than healthy adults (Tøien et al., 2023). Therefore, V waves increased after training may be beneficial for improving lower limb explosive strength.

This study also showed a significant moderate negative correlation between H-index and 30 m sprint time. NCV reflects the velocity transmitted along a motoneuron of the impulse, while rapid NCV may accelerate muscle contraction, leading to a higher speed in 30 m (Domkundwar et al., 2017; Vonbank et al., 2023). Research investigating NCV in sprint performance is limited. A study of the posterior tibial NCV of athletes indicated that male sprinters have higher NCV than marathoners and lower NCV than distance runners and weight lifters (Kamen et al., 1984). In addition, one study found that the reaction time strongly correlated with 100 m running time, finalists’ reaction time were shorter significantly than semifinalists in athletic world championships (Tonnessen et al., 2013). Higher NCV may shorten the reaction time, potentially helping sprinters shorten the 100 m running time (Crotty et al., 2022). The central neurotransmissions in auditory and sensorimotor systems were found to correlate with 100 m performance, and existing significant differences between elite and sub-elite adolescent sprinters (Hsieh et al., 2024). Thus, the excitability of motor neurons and nerve conduction in the cerebral cortex has a significant impact on improving sprint performance.

High levels of eccentric strength of the hamstring were found to strongly correlate with 30 m performance in this study, also as a predictor of 30 m sprint time, consistent with previous research. Hamstrings contract eccentrically as knee flexors to decelerate the momentum of the tibia and prevent knee hyperextension during the terminal swing phase, which may contribute to increasing step length and energy efficiency (Guex and Millet, 2013; Guruhan et al., 2021). Previous studies also found a large correlation between maximum velocity (Vmax) and isoinertial eccentric force (r = 0.56) in sprinters. The eccentric force can help sprinters adjust lower limb stiffness to exhibit high levels of reactive strength and maintain higher speeds (Douglas et al., 2020). Brady et al. (2020) reported that peak force, RFD and impulse of Isometric mid-thigh pull and Isometric squat significantly correlate with 0–5 m performance in sprinters. Only the peak force of IMTP correlated with 0–30 m (r = −0.595). Greater sprinters were observed to have larger muscle volumes of hamstrings, which strongly correlated with 40 m sprint time (r = −0.670, p < 0.01) (Nuell et al., 2021). Meanwhile, eccentric strength deficits in the hamstrings are common factors causing injury to sprinters, and enhancing eccentric strength training of the hamstrings may reduce the incidence of injury (Alt et al., 2021; Rudisill et al., 2023). A rehabilitation protocol consisting of eccentric exercises is more effective for elite sprinters with acute hamstring injuries, helping them return to training or competition quickly (Askling et al., 2014; Hickey et al., 2022).

The current results also showed a positive correlation between active tendon stiffness in the ankle joint and 30 m sprint time, inferring that relatively compliant tendons are beneficial for utilizing elastic energy. Tendon stiffness of plantar flexors was considered important enough to probably affect the storage and release of elastic energy, contributing significantly to propulsive and upward impulses (Aeles et al., 2018; Crotty et al., 2024). No significant differences in the active tendon stiffness of the plantar flexors were observed between sprinters and untrained individuals (Kubo et al., 2011; Kubo et al., 2017). Previous studies have found the Achilles tendon stiffness of sprinters during ballistic contractions is lower than during ramp contractions, which means the Achilles tendon stiffness of sprinters is more compliant when sprinting and jumping, similar to the results of this study (Kubo et al., 2020). The data predicted by a full-body musculoskeletal model showed that tendon compliance has minimal effort in sprint performance, a 10% increase in tendon compliance results in a 0.3% increase in maximum sprinting speed (Lin and Pandy, 2022). This study also indicates that tendon stiffness may not be a predictor of sprint performance. However, plantar flexor passive stiffness was negatively correlated with 100 m performance (r = −0.334, p = 0.018) in well-trained male sprinters (Takahashi et al., 2018). In addition, studies reported the correlation between other muscle-tendon parameters and sprint performance. The cross-sectional area and length of the Achilles tendon positively correlated with the running velocity and power of a 20 m sprint (Monte and Zamparo, 2019). The length of the Achilles tendon also has no correlation with 100 m performance (Tomita et al., 2021). The muscle volume of plantar flexors showed no differences between elite and sub-elite sprinters, but elite sprinters have higher muscle volume of hip extensors (Miller et al., 2022; Miller et al., 2021).

Sprinters need to apply vertical and horizontal forces to the ground rapidly to generate explosive contractions from a stationary position at the start; therefore, sprinters exhibit higher RFD and impulses (Slawinski et al., 2010). Previous studies found that vertical jump performance of top sprinters is correlated with top-speed phases, and the mean propulsive power in vertical jumps of elite sprinters is also correlated with sprint time (Loturco et al., 2018; Loturco et al., 2019). In this study, RFD correlated with Hmax/Mmax, eccentric strength of the quadriceps and vertical stiffness. Hmax/Mmax is an indicator of the α-motoneurons excitability from the Ia afferent and also reflects the stretch reflex, influencing the performance of the SSC (Leukel et al., 2008; Sun et al., 2022). CMJ requires the subject’s lower limb to start with an eccentric contraction, excited Ia afferent and increased spinal α-motoneurons excitability, leading to a large eccentric strength of the quadriceps. Eccentric contractions generate greater strength of the lower limb, making the subsequent concentric contraction faster and resulting in a higher RFD. Previous studies have shown that faster sprinters with higher vertical force achieve greater acceleration during the maximal speed phase (Nagahara et al., 2024; Nagahara et al., 2018). Sprinters reduce ground contact time by greater vertical stiffness, and their lower limbs are regularly subject to high-ground reaction forces (Maloney and Fletcher, 2021). A large difference between sprinters and untrained individuals in leg stiffness may be because the sprinter has a shorter ground contact time (Douglas et al., 2018). Greater vertical stiffness reflects improved neuromuscular control, helping sprinters move rapidly. Although the vertical stiffness significantly correlated with RFD in this study, RFD and vertical stiffness were both calculated by the peak force of the eccentric phase of the CMJ test. In the eccentric phase, shorter time leads to smaller ΔCOM, which may result in a spurious correlation and can be explored and validated further.

This study had several limitations. First, the sample size of this study is small because of limited access to elite male college sprinters, which limits statistical power and generalizability. Thus, these findings should be approached with caution. Further research is needed to increase the sample size and groups to explore the neuromuscular function of different-level sprinters. Second, the H reflex and M wave test in this study were in rest, the H-reflex and M-wave during muscle contraction could also be further explored, which better reflects neural modulation of actual movement. Third, this study only tested a 30 m sprint, without a 100 m test. Finally, the subjects were only male sprinters.

In summary, sprinters require strong neuromuscular control ability, and neural factors from the cortex are the primary determinants of lower limb explosiveness. H reflex and V-wave were sensitive to changes in neural function, which can be used to monitor changes in α-motoneurons excitability and assess the fatigue of the central and peripheral nervous system in a training period. In addition, NCV was found to correlate with a 30 m sprint performance, future research could explore the relationship between NCV and sports performance in higher-level sprinters.

This study found that V/MmaxA and HECC were predictive factors of 30 m sprint time, vertical stiffness and QECC were the predictive factors of RFD. Neural factors such as the α-motoneurons excitability of the spinal and supraspinal centers, have a greater influence on lower limb explosive strength in male college sprinters. Therefore, training related to the neural function of sprinters should be emphasized. In addition, H reflex and V wave can be used widely to assess and monitor the neural function of sprinters in future research. The impact of neural drive on muscles in different levels and sexes of sprinters, and the neuromuscular modulation during muscle contractions can be further explored.