Elsevier

Journal of Biomechanics

Volume 44, Issue 6, 7 April 2011, Pages 1104-1107
Journal of Biomechanics

Changes in running mechanics and spring–mass behavior induced by a mountain ultra-marathon race

https://doi.org/10.1016/j.jbiomech.2011.01.028Get rights and content

Abstract

Changes in running mechanics and spring–mass behavior due to fatigue induced by a mountain ultra-marathon race (MUM, 166 km, total positive and negative elevation of 9500 m) were studied in 18 ultra-marathon runners. Mechanical measurements were undertaken pre- and 3 h post-MUM at 12 km h−1 on a 7 m long pressure walkway: contact (tc), aerial (ta) times, step frequency (f), and running velocity (v) were sampled and averaged over 5–8 steps. From these variables, spring–mass parameters of peak vertical ground reaction force (Fmax), vertical downward displacement of the center of mass (Δz), leg length change (ΔL), vertical (kvert) and leg (kleg) stiffness were computed. After the MUM, there was a significant increase in f (5.9±5.5%; P<0.001) associated with reduced ta (−18.5±17.4%; P<0.001) with no change in tc, and a significant decrease in both Δz and Fmax (−11.6±10.5 and −6.3±7.3%, respectively; P<0.001). kvert increased by 5.6±11.7% (P=0.053), and kleg remained unchanged. These results show that 3 h post-MUM, subjects ran with a reduced vertical oscillation of their spring–mass system. This is consistent with (i) previous studies concerning muscular structure/function impairment in running and (ii) the hypothesis that these changes in the running pattern could be associated with lower overall impact (especially during the braking phase) supported by the locomotor system at each step, potentially leading to reduced pain during running.

Introduction

During running, the mechanical behavior of the musculoskeletal structures of the lower limbs is often described as that of a spring–mass system bouncing onto the ground (Blickhan, 1989, Dickinson et al., 2000, McMahon and Cheng, 1990). This model has been used to describe and study the mechanics and energetics of bouncing and running gaits (Ferris et al., 1998, He et al., 1991, Heise and Martin, 1998, Morin et al., 2007), and consists of a point mass supported by a single massless linear “leg spring”. Thus, the main mechanical parameter studied when using the spring–mass model is the stiffness of the leg spring, which is the ratio of the maximal force in the spring to the maximum leg compression at the middle of the stance phase. Moreover, the vertical stiffness is used to describe the vertical motion of the center of mass (COM) during contact (Farley and Gonzalez, 1996, McMahon and Cheng, 1990), and is defined as the ratio of the maximal force to the vertical displacement of the COM as it reaches its lowest point, i.e. at the middle of the stance phase.

The mechanical variables describing this spring–mass behavior are integrative and encompass numerous neuromuscular and mechanical phenomena simultaneously characterizing the running system (Farley and Ferris, 1998). They may be of interest when studying how extreme fatigue conditions and damage to the locomotor system may affect running mechanics during long or ultra-long distance running. In the past very few studies focused on running mechanics over long distance races (e.g. Kyrolainen et al., 2000, Nicol et al., 1991) but this is changing: studies on a 24-h treadmill run (24TR), recently focused on the physiological factors associated with performance (Millet, in press, Millet et al., 2011), neuromuscular fatigue (Martin et al., 2010) and changes in running mechanics and spring–mass characteristics (Morin et al., in press). We showed that the spring–mass behavior significantly changed after a 24TR, with ∼5% higher step frequency (caused by a decrease in contact time, with unchanged aerial time) and 4.4% lower peak ground reaction forces (GRF). Furthermore, the vertical displacement of the COM and the leg length change during contact were lower, which resulted in ∼10% higher vertical and leg stiffness values. While no comparable data exist for ultra-marathons, overall these results were very consistent with studies which observed an impairment of muscular function, i.e. after a 160-day running trip from Paris to Beijing (Millet, in press, Millet et al., 2009), a muscular biopsy of the vastus lateralis (Morin et al., 2009), or with ageing (Cavagna et al., 2007, Karamanidis and Arampatzis, 2005). One exception was that the higher step frequency observed in these protocols was caused by a lower aerial time, with no change in contact time, in opposition to the 24TR protocol (i.e. higher step frequency but lower contact time and no change in aerial time). Furthermore, the changes reported post-24TR were hypothesized to tend towards the same functional consequence: possibly contributing to an overall limitation of the potentially painful consequences of ultra-long distance runs on a subject's musculoskeletal system, mainly because running with a higher step frequency and thus a lower amplitude of oscillation of the COM could help lower the overall eccentric action of the lower limbs' extensor muscles at each step, these actions becoming painful with increasing run duration and fatigue.

One limitation of the 24TR study was that it was not a typical overground race; neither did it account for the effect of negative elevation and the corresponding eccentric load. Thus, our aim was to study the changes in the main running mechanics and spring–mass variables after a mountain ultra-marathon race (MUM) performed in actual race conditions. We hypothesized that larger changes than those reported after the 24TR would be observed given (i) the longer duration of the run and (ii) the tougher running conditions especially with the higher eccentric load induced by downhill running. The originality of this study is that it was performed during an international MUM, one of the hardest exercises performed by humans in race conditions.

Section snippets

Subjects and protocol overview

Thirty-four subjects initially volunteered for this study after complete medical examination, but only 22 were able to complete the MUM. All the subjects were experienced ultra-marathon runners with 13 years of running and 5 years of ultra-endurance training. Among these 22 subjects, 4 were unable to complete all the mechanical measurements at the imposed running velocity. Therefore, only the data of the remaining 18 subjects were analyzed in the present pre-/3 h post-MUM comparison. Their main

Results

The subjects studied ran the MUM in 37.9±6.2 h (range 23.5–46 h, data from the race organizers). The changes in the main running mechanics are reported in Table 1. Subjects ran 3 h post-MUM with significantly (P<0.001) reduced ta, increased f and reduced Fmax and Δz. These changes were accompanied by a nearly significant (P=0.053) change in kvert, which increased by 6.01% on average for the group. No change was observed in tc or kleg.

The sub-groups comparison showed that none of the tested

Discussion

The main result of this study was that after a MUM run over 166 km and with more than 9000 m of altitude change – which represented ∼23–46 h of running/walking – subjects modified their running pattern towards a significantly higher step frequency by reducing their aerial time. This was associated with a lower vertical GRF, a reduced vertical oscillation of the COM, and a strong tendency (P=0.053) towards a higher vertical stiffness. All these significant changes were of large magnitude (absolute

Conflict of interest statement

The authors do not have any conflict of interest or personal relationships with other people or organizations that could inappropriately influence this work.

Acknowledgements

The authors warmly thank the subjects of the present study for their willingness to participate and their cheerfulness before, during and especially after the race. We would also like to thank the organizers of ‘The North-Face® Ultra-Trail du Mont-Blanc®’ and the ‘Ecole Nationale de Ski et d'Alpinisme’ in Chamonix, France, for their help in data collection and the magazine ‘Ultrafondus’ for their help in recruiting subjects. Katja Tomazin is financially supported by Saint-Etienne Métropole.

References (25)

  • C.T. Farley et al.

    Biomechanics of walking and running: center of mass movements to muscle action

    Exerc. Sport Sci. Rev.

    (1998)
  • D.P. Ferris et al.

    Running in the real world: adjusting leg stiffness for different surfaces

    Proc. R. Soc. B

    (1998)
  • Cited by (91)

    • Effect of heat pre-conditioning on recovery following exercise-induced muscle damage

      2021, Current Research in Physiology
      Citation Excerpt :

      A possible explanation would be that the extent of muscle damage experienced by our participants may not have been severe enough to result in sustained decrease in running economy, or appreciably alter stride kinematics, given that such mechanical changes (and associated changes in VO2) are adopted to minimize pain during the eccentric phase and overall load experienced by locomotor system (Morin et al., 2011). Additionally, spring mass characteristics in the aforementioned studies were examined 0–3 ​h following prolonged running (Morin et al., 2011; Degache et al., 2013), which would have been influenced by both EIMD and fatigue. As such, further studies employing more aggressive muscle damage protocols are warranted to understand and profile the mechanical changes following EIMD.

    View all citing articles on Scopus
    View full text