Changes in sprint performance and sagittal plane kinematics after heavy resisted sprint training in professional soccer players

Abstract

Background: Sprint performance is an essential skill to target within soccer, which can be likely achieved with a variety of methods, including different on-field training options. One such method could be heavy resisted sprint training. However, the effects of such overload on sprint performance and the related kinetic changes are unknown in a professional setting. Another unknown factor is whether violating kinematic specificity via heavy resistance will lead to changes in unloaded sprinting kinematics. We investigated whether heavy resisted sled training (HS) affects sprint performance, kinetics, sagittal plane kinematics, and spatiotemporal parameters in professional male soccer players.

Methods: After familiarization, a nine-week training protocol and a two-week taper was completed with sprint performance and force-velocity (FV) profiles compared before and after. Out of the two recruited homogenous soccer teams (N = 32, age: 24.1 ± 5.1 years: height: 180 ± 10 cm; body-mass: 76.7 ± 7.7 kg, 30-m split-time: 4.63 ± 0.13 s), one was used as a control group continuing training as normal with no systematic acceleration training (CON, N = 13), while the intervention team was matched into two HS subgroups based on their sprint performance. Subgroup one trained with a resistance that induced a 60% velocity decrement from maximal velocity (N = 10, HS60%) and subgroup two used a 50% velocity decrement resistance (N = 9, HS50%) based on individual load-velocity profiles.

Results: Both heavy resistance subgroups improved significantly all 10-30-m split times (p < 0.05, d = - 1.25; -0.62). Post-hoc analysis showed that HS50% improved significantly more compared to CON in 0-10-m split-time (d = 1.03) and peak power (d = 1.16). Initial maximal theoretical horizontal force capacity (F0) and sprint FV-sprint profile properties showed a significant moderate relationship with F0 adaptation potential (p < 0.05). No significant differences in sprinting kinematics or spatiotemporal variables were observed that remained under the between-session minimal detectable change.

Conclusion: With appropriate coaching, heavy resisted sprint training could be one pragmatic option to assist improvements in sprint performance without adverse changes in sprinting kinematics in professional soccer players. Assessing each player's initial individual sprint FV-profile may assist in predicting adaptation potential. More studies are needed that compare heavy resisted sprinting in randomized conditions.

Keywords: Coordination; Professional sport; Resistance training; Sprinting; Strength training; Velocity-based training.

Conflict of interest statement

The authors declare there are no competing interests.

©2020 Lahti et al.

Figures

Figure 1. Training program design.

HS: Heavy Sled, *: sled velocity verification was completed on week 1, filming of sled technique on week 2, RECO: recovery time between sprints, m: meters, FV: Force-velocity, #: camp training included two sprints with rubber bands and 2×2 free sprints on separate days.

Figure 2. Sprint split-time changes.

Raw Changes in split time performance with MDC thresholds (A) and their corresponding effect sizes within each group with ES thresholds (B). The lines between the four split-time measurements (0-5, 0-10, 0-20, 0-30) have been smoothed. The error ribbons represent standard error via bias corrected and accelerated bootsrapping at 0.68 confidence intervals, corresponding to +/- 1 standard deviation. HS: Heavy sled, CON: control group, MDC: Minimal detectable change.

Figure 3. Mechanical variable correlations.

Correlation coefficients between initial values in (A) maximal theoretical horizontal force (F0) production, (B) initial Sprint FV-profile (-F0/v0), and respective changes post intervention. HS: Heavy sled, CON: control group, *: p < 0.05, **: p < 0.01.

Figure 4. Sprint kinematic and spatiotemporal changes, immediate effects of sled.

Immediate kinematic and spatiotemporal differences between early acceleration (black) and sled sprinting (gray). Touchdown (A, B) and toe –off (C, D) within HS60% and HS50% groups. HS: Heavy sled, CT: Contact time, SR: Step Rate, SL: Step Length relative to body height, CM: Center of Mass, IPSI: Ipsilateral (ground contact leg), m: meter, *: p < 0.05. No group differences were found (p < 0.05).

Figure 5. Pre-post intervention sprint kinematic changes in early acceleration and upright sprinting.

Touchdown (A, B, C, J, I, K) and toe –off (D, E, F, H, J, L) within HS60%, HS50%, and CON groups. In early acceleration, toe-off is based on the average of the first push toe-off from the sprint start and the first two steps toe-off. The touchdown is based on the first 3 steps. Upright sprinting toe-off and touchdown are analyzed from 2 steps during upright sprinting at our close to maximal velocity (∼22.5 m). No kinematic variables for within and between-group comparisons reached significance. HS: Heavy sled, CT: Contact time, SR: Step rate, SL: Step Length relative to body height, CM: Center of Mass. *: Significant within-group difference (p < 0.05).