Elsevier

Journal of Biomechanics

Volume 48, Issue 12, 18 September 2015, Pages 3149-3154
Journal of Biomechanics

Acceleration capability in elite sprinters and ground impulse: Push more, brake less?

https://doi.org/10.1016/j.jbiomech.2015.07.009Get rights and content

Abstract

Overground sprint studies have shown the importance of net horizontal ground reaction force impulse (IMPH) for acceleration performance, but only investigated one or two steps over the acceleration phase, and not in elite sprinters. The main aim of this study was to distinguish between propulsive (IMPH+) and braking (IMPH) components of the IMPH and seek whether, for an expected higher IMPH, faster elite sprinters produce greater IMPH+, smaller IMPH, or both.

Nine high-level sprinters (100-m best times range: 9.95–10.60 s) performed 7 sprints (2×10 m, 2×15 m, 20 m, 30 m and 40 m) during which ground reaction force was measured by a 6.60 m force platform system. By placing the starting-blocks further from the force plates at each trial, and pooling the data, we could assess the mechanics of an entire “virtual” 40-m acceleration.

IMPH and IMPH+ were significantly correlated with 40-m mean speed (r=0.868 and 0.802, respectively; P<0.01), whereas vertical impulse and IMPH were not. Multiple regression analyses confirmed the significantly higher importance of IMPH+ for sprint acceleration performance. Similar results were obtained when considering these mechanical data averaged over the first half of the sprint, but not over the second half. In conclusion, faster sprinters were those who produced the highest amounts of horizontal net impulse per unit body mass, and those who “pushed more” (higher IMPH+), but not necessarily those who also “braked less” (lower IMPH) in the horizontal direction.

Introduction

Accelerating ones own body mass is a key determinant of performance in many sports such as soccer or rugby, but first and foremost in the sprint events. In the 100-m dash, the full acceleration phase (i.e. from the start to the maximal running velocity reached after about 40–70 m) has been shown to be directly related to performance (Delecluse, 1997, Delecluse et al., 1995, Mero, 1988, Mero et al., 1992). Basic laws of dynamics and experimental data explain that acceleration in the forward direction is related to the amount of net horizontal force and impulse produced and applied onto the ground, which will be returned through the ground reaction force (GRF) impulse, thereafter referred to as impulse (Hunter et al., 2005, Kawamori et al., 2012, Mero, 1988).

In the sagittal plane of motion, vertical (FV) and horizontal (FH) components of the resultant GRF, and the corresponding impulses (IMPV and IMPH, respectively) are the main determinants of the running motion and center of mass displacement. However, although FV production has been related to the ability to achieve high maximal running speeds in humans (Weyand et al., 2010, Weyand et al., 2000), FH and the associated forward orientation of resultant GRF vector have recently been clearly put forward as a major determinant of acceleration and 100-m performance (Kugler and Janshen, 2010, Morin et al., 2011, Morin et al., 2012, Rabita et al., 2015). Furthermore, previously mentioned studies found that vertical impulse was either very poorly (Hunter et al., 2005) or not significantly correlated (Kawamori et al., 2012) with acceleration performance.

Since a typical running support phase may be divided into a braking phase (backward orientation of the FH vector; braking impulse IMPH−) and a propulsive phase (forward orientation of the FH vector; propulsive impulse IMPH+), the net horizontal impulse IMPH is the sum of IMPH and IMPH+. Consequently, a given amount of IMPH could result from many combinations of IMPH and IMPH+ values. Therefore, in practical terms, to accelerate well (i.e. produce a high IMPH), a sprinter could push more (i.e. increase IMPH+) and/or brake less (i.e. decrease IMPH), and the sprint training process could be related to these possibilities. In addition, previous studies on accelerated walking in humans (Orendurff et al., 2008, Peterson et al., 2011) and accelerated locomotion in animals (McGowan et al., 2005, Roberts and Scales, 2002, Walter and Carrier, 2009) have shown that forward acceleration of the body could be achieved by modulating IMPH and IMPH+, provided that IMPH increased.

In the area of sprint running performance, it is interesting to note that few studies have specifically addressed the issue of the relative importance of IMPH and its braking and propulsive components for acceleration performance. Hunter et al. (2005) measured GRF impulses for one single step at the 16-m mark of a typical 25-m sprint in 36 non-specialist athletes. These authors showed that relative (i.e. normalized to body mass) IMPH and IMPH+ were the strongest predictors of sprint velocity. Using simple linear regression, IMPH− was not related to sprint velocity (r2=0.04). When entering both IMPH and IMPH+ in a multiple regression model, these two variables explained significant parts of the variance in running velocity: 7% and 57%, respectively. These authors highlighted the importance of the multiple regression approach to test the relationship between acceleration performance and both IMPH− and IMPH+, independently from one another. Furthermore, they commented on the fact that although relative IMPH− accounted for a small proportion (7%) of the variance in sprint velocity, further studies were needed to find out whether “faster athletes actually minimized their magnitude of braking”. Using a very similar protocol (30 team sport players performed 10-m sprints, and impulses were computed from GRF recorded over one single step for the first contact, and the contact at 8 m after the start), Kawamori et al. (2012) showed that relative IMPH and IMPH+ measured at 8 m were significantly correlated with 10-m time, but relative IMPV and IMPH were not. The authors therefore discussed the “lack of evidence that smaller braking impulse was associated with better sprint acceleration performance”. Finally, Mero (1988) studied the first contact following the starting-blocks push-off in 4 sprinters and showed that IMPV was not significantly correlated to running velocity, whereas IMPH+ was. However, they did not detail the correlations with IMPH and IMPH.

The main limitation of these studies is that impulses were only measured for one to five steps over an entire acceleration, and/or included non-specialist sprinters of heterogeneous levels of performance, and/or data of IMPH+ and IMPH were not analyzed using a multiple regression model. This statistical approach makes possible to investigate the complementary effects of several independent variables together. In the present study, we had the unique opportunity to measure GRF impulses for almost all steps of 40-m sprints in elite and sub-elite sprinters, and thus to experimentally address the question of whether elite sprint acceleration performance depends on “pushing more” and/or on “braking less” in the horizontal direction.

The first aim of this study was to investigate the relationships between GRF impulses produced over a 40-m sprint and overall acceleration performance in elite sprinters. Our hypothesis was that relative IMPV would not be significantly correlated with performance, but relative IMPH would. The second aim was to investigate the independent relative importance of horizontal braking and propulsive impulses.

Section snippets

Subjects and experimental protocol

Nine male elite (international level) or sub-elite (French national level) sprinters (mean±SD: age=23.9±3.4 years; body mass=76.4±7.1 kg; height=1.82±0.07 m) gave their written informed consent to participate in this study, conducted according to the declaration of Helsinki II, and approved by the local ethical committee. Their personal 100-m best times at the moment of the study were 10.37±0.27 s (range: 9.95–10.60 s).

The sprinters were tested on the indoor track of the French Institute of Sport

Results

40-m times were 5.10±0.24 s (ranging from 4.81 to 5.58 s). This corresponded to V40 of 7.86±0.36 m s−1 (ranging from 7.17 to 8.32 m s−1). Table1 shows the main mechanical variables, and Fig. 1 shows the values of IMPH, IMPH− and IMPH+ for all the running steps analyzed over the 40-m.

Fig. 1 shows that step after step during the sprint acceleration, IMPH decreased first due to the decrease in IMPH+ (first 6–7 steps), and then due to the higher IMPH−. This detailed analysis of IMPH+ is further shown in

Discussion

The main results of this study of high-level sprinters were that:

  • (1)

    In accordance with our hypothesis, relative vertical GRF impulse averaged over the entire 40-m was not correlated to sprint acceleration performance, whereas relative horizontal net impulse was;

  • (2)

    Within this horizontal net impulse, propulsive impulse explained an important part (about 75%) of the performance variability between athletes (i.e. faster sprinters were those who showed the highest values of propulsive impulse), whereas

Conflict of interest

We declare that we have no conflict of interest.

Acknowledgements

The authors are grateful to Dr Pascal Edouard for his valuable input in the discussion of the present data. We also thank Guy Ontanon, Dimitri Demonière, Michel Gilot and the athletes of the National Institute of Sport (INSEP) who voluntarily gave their best performance and patience for this protocol. We are grateful to Gaël Guilhem, Caroline Giroux, Stevy Farcy, and Virha Despotova for their collaboration during the experimentations.

References (19)

  • F. Kugler et al.

    Body position determines propulsive forces in accelerated running

    J. Biomech.

    (2010)
  • M.S. Orendurff et al.

    Kinetic mechanisms to alter walking speed

    Gait Posture

    (2008)
  • C.L. Peterson et al.

    Braking and propulsive impulses increase with speed during accelerated and decelerated walking

    Gait Posture

    (2011)
  • C. Delecluse

    Influence of strength training on sprint running performance. Current findings and implications for training

    Sports Med.

    (1997)
  • C. Delecluse et al.

    Analysis of 100 m sprint performance as a multidimensional skill

    J. Hum. Mov. Stud.

    (1995)
  • J.P. Hunter et al.

    Relationships between ground reaction force impulse and kinematics of sprint-running acceleration

    J. Appl. Biomech.

    (2005)
  • N. Kawamori et al.

    Relationships between ground reaction impulse and sprint acceleration performance in team-sport athletes

    J. Strength Cond. Res.

    (2012)
  • C. McGowan et al.

    Joint work and power associated with acceleration and deceleration in tammar wallabies (Macropus eugenii)

    J. Exp. Biol.

    (2005)
  • A. Mero

    Force-time characteristics and running velocity of male sprinters during the acceleration phase of sprinting

    Res. Q. Exerc. Sport

    (1988)
There are more references available in the full text version of this article.

Cited by (95)

  • Prediction of ground reaction forces using the artificial neural network from capacitive self-sensing values of composite ankle springs for exo-robots

    2022, Composite Structures
    Citation Excerpt :

    The ground reaction force (GRF), one of the most significant running kinetic parameters, is used as an indicator to analyze human running locomotion and prevent injury [1–3]. Some studies have shown that the GRF is related to sprint-running acceleration and running speed, and an excessive GRF is related to the risk of running injury [4–6]. Generally, the GRF is measured through a force plate embedded in a treadmill; however, this method has restricted usability and is inferior in terms of equipment cost and spatial requirements [7].

  • Kinematic factors associated with start performance in World-class male sprinters

    2021, Journal of Biomechanics
    Citation Excerpt :

    This is supported by data from the block phase in 103 male and 51 female trained sprinters, presented by Willwacher et al. (2016), which showed r values across all 154 participants of 0.91 and 0.52 respectively for change in horizontal velocity and block time in relation to NAHEP. The importance of horizontal impulse to sprint acceleration performance is well established (Hunter et al., 2005; Morin et al., 2015). Impulse is the product of the force produced and the time taken to produce it and, when divided by body mass, equates to the change in velocity of the athlete.

View all citing articles on Scopus
View full text