Recent literature supports the importance of horizontal ground reaction force (GRF) production for sprint acceleration performance. Modeling and clinical studies have shown that the hip extensors are very likely contributors to sprint acceleration performance. We experimentally tested the role of the hip extensors in horizontal GRF production during short, maximal, treadmill sprint accelerations. Torque capabilities of the knee and hip extensors and flexors were assessed using an isokinetic dynamometer in 14 males familiar with sprint running. Then, during 6-s sprints on an instrumented motorized treadmill, horizontal and vertical GRF were synchronized with electromyographic (EMG) activity of the vastus lateralis, rectus femoris, biceps femoris and gluteus maximus averaged over the first half of support, entire support, entire swing and end-of-swing phases. No significant correlations were found between isokinetic or EMG variables and horizontal GRF. Multiple linear regression analysis showed a significant relationship (P = 0.024) between horizontal GRF and the combination of biceps femoris EMG activity during the end of the swing and the knee flexors eccentric peak torque. In conclusion, subjects who produced the greatest amount of horizontal force were both able to highly activate their hamstring muscles just before ground contact and present high eccentric hamstring peak torque capability.

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, comparison and the neuromuscular mechanisms for any differences have 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 were measured in three 50-ms time windows from their onset and were normalized 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 twofold that of controls. Athletes had greater normalized 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 normalized 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 normalized tetanic RFD between groups. The differences in voluntary normalized RFD between athletes and controls were explained by agonist muscle neural activation and not by the similar intrinsic contractile properties of the groups.

The purpose of this study was to investigate the relationship between movement velocity and relative load in three lower limbs exercises commonly used to develop strength: leg press, full squat and half squat. The percentage of one repetition maximum (%1RM) has typically been used as the main parameter to control resistance training; however, more recent research has proposed movement velocity as an alternative. Fifteen participants performed a load progression with a range of loads until they reached their 1RM. Maximum instantaneous velocity (V_max) and mean propulsive velocity (MPV) of the knee extension phase of each exercise were assessed. For all exercises, a strong relationship between V_max and the %1RM was found: leg press (r²_adj = 0.96; 95% CI for slope is [−0.0244, −0.0258], P < 0.0001), full squat (r²_adj = 0.94; 95% CI for slope is [−0.0144, −0.0139], P < 0.0001) and half squat (r²_adj = 0.97; 95% CI for slope is [−0.0135, −0.00143], P < 0.0001); for MPV, leg press (r²_adj = 0.96; 95% CI for slope is [−0.0169, −0.0175], P < 0.0001, full squat (r²_adj = 0.95; 95% CI for slope is [−0.0136, −0.0128], P < 0.0001) and half squat (r²_adj = 0.96; 95% CI for slope is [−0.0116, 0.0124], P < 0.0001). The 1RM was attained with a MPV and V_max of 0.21 ± 0.06 m s⁻¹ and 0.63 ± 0.15 m s⁻¹, 0.29 ± 0.05 m s⁻¹ and 0.89 ± 0.17 m s⁻¹, 0.33 ± 0.05 m s⁻¹ and 0.95 ± 0.13 m s⁻¹ for leg press, full squat and half squat, respectively. Results indicate that it is possible to determine an exercise-specific %1RM by measuring movement velocity for that exercise.

This study aimed (i) to explore the relationship between vertical (jumping) and horizontal (sprinting) force–velocity–power (FVP) mechanical profiles in a large range of sports and levels of practice, and (ii) to provide a large database to serve as a reference of the FVP profile for all sports and levels tested. A total of 553 participants (333 men, 220 women) from 14 sport disciplines and all levels of practice participated in this study. Participants performed squat jumps (SJ) against multiple external loads (vertical) and linear 30–40 m sprints (horizontal). The vertical and horizontal FVP profile (i.e., theoretical maximal values of force (F₀), velocity (v₀), and power (P_max)) as well as main performance variables (unloaded SJ height in jumping and 20-m sprint time) were measured. Correlations coefficient between the same mechanical variables obtained from the vertical and horizontal modalities ranged from −0.12 to 0.58 for F₀, −0.31 to 0.71 for v₀, −0.10 to 0.67 for P_max, and −0.92 to −0.23 for the performance variables (i.e, SJ height and sprint time). Overall, results showed a decrease in the magnitude of the correlations for higher-level athletes. The low correlations generally observed between jumping and sprinting mechanical outputs suggest that both tasks provide distinctive information regarding the FVP profile of lower-body muscles. Therefore, we recommend the assessment of the FVP profile both in jumping and sprinting to gain a deeper insight into the maximal mechanical capacities of lower-body muscles, especially at high and elite levels.

Purpose:: To analyze the reliability and validity of a simple computation method to evaluate force (F), velocity (v), and power (P) output during a countermovement jump (CMJ) suitable for use in field conditions and to verify the validity of this computation method to compute the CMJ force–velocity (F–v) profile (including unloaded and loaded jumps) in trained athletes.Methods:: Sixteen high-level male sprinters and jumpers performed maximal CMJs under 6 different load conditions (0–87 kg). A force plate sampling at 1000 Hz was used to record vertical ground-reaction force and derive vertical-displacement data during CMJ trials. For each condition, mean F, v, and P of the push-off phase were determined from both force-plate data (reference method) and simple computation measures based on body mass, jump height (from flight time), and push-off distance and used to establish the linear F–v relationship for each individual.Results:: Mean absolute bias values were 0.9% (± 1.6%), 4.7% (± 6.2%), 3.7% (± 4.8%), and 5% (± 6.8%) for F, v, P, and slope of the F–v relationship (S_Fv), respectively. Both methods showed high correlations for F–v-profile-related variables (r = .985–.991). Finally, all variables computed from the simple method showed high reliability, with ICC >.980 and CV <1.0%.Conclusions:: These results suggest that the simple method presented here is valid and reliable for computing CMJ force, velocity, power, and F–v profiles in athletes and could be used in practice under field conditions when body mass, push-off distance, and jump height are known.

We analysed the changes in force-velocity-power variables and jump performance in response to an individualized training program based on the force-velocity imbalance (FV_imb). In particular, we investigated (i) the individual adaptation kinetics to reach the optimal profile and (ii) de-training kinetics over the three weeks following the end of the training program. Sixty subjects were assigned to four sub-groups according to their initial FV_imb: high or low force-deficit (FD) and high or low velocity-deficit (VD). The duration of training intervention was set so that each individual reached their “Optimal force-velocity (F-v) profile”. Mechanical and performance variables were measured every 3 weeks during the program, and every week after the end of the individualized program. All subjects in the FD sub-groups showed extremely large increases in maximal theoretical force output (+30±16.6% Mean±SD; ES = 2.23±0.28), FV_imb reduction (-74.3±54.7%; ES = 2.17±0.27) and large increases in jump height (+12.4±7.6%; ES = 1.45±0.23). For the VD sub-groups, we observed moderate to extremely large increases in maximal theoretical velocity (+15.8±5.1%; ES = 2.72±0.29), FV_imb reduction (-19.2±6.9%; ES = 2.36±0.35) and increases in jump height (+10.1±2.7%; ES = 0.93±0.09). The number of weeks needed to reach the optimal F-v profile (12.6 ± 4.6) was correlated to the magnitude of initial FV_imb (r = 0.82, p<0.01) for all participants regardless of their initial subgroup. No significant change in mechanical variables or jump performance was observed over the 3-week de-training period. Collectively, these results provide useful insights into a more specific, individualized (i.e. based on the type and magnitude of FV_imb) and accurate training prescription for jumping performance. Considering both training content and training duration together with FV_imb may enable more individualized, specific and effective training monitoring and periodization.