JOURNAL OF SPORTS SCIENCES, 2017 VOL. 35, NO. 6, 531–538 http://dx.doi.org/10.1080/02640414.2016.1175655
Are gait characteristics and ground reaction forces related to energy cost of running in elite Kenyan runners? J. Santos-Concejeroa,b, N. Tamb, D. R. Coetzeeb, J. Olivánc, T. D. Noakesb and R. Tuckerb,d a Department of Physical Education and Sport, University of the Basque Country UPV/EHU, Vitoria-Gasteiz, Spain; bDivision for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Cape Town, South Africa; cDepartment of Physiology, European University of Madrid, Madrid, Spain; dSchool of Medicine, University of the Free State, Bloemfontein, South Africa
ABSTRACT
ARTICLE HISTORY
The aim of this study was to determine whether gait cycle characteristics are associated with running economy in elite Kenyan runners. Fifteen elite Kenyan male runners completed two constant-speed running sets on a treadmill (12 km ·h−1 and 20 km ·h−1). VO2 and respiratory exchange ratio values were measured to calculate steady-state oxygen and energy cost of running. Gait cycle characteristics and ground contact forces were measured at each speed. Oxygen cost of running at different velocities was 192.2 ± 14.7 ml· kg−1· km−1 at 12 km· h−1 and 184.8 ± 9.9 ml· kg−1· km−1 at 20 km· h−1, which corresponded to a caloric cost of running of 0.94 ± 0.07 kcal ·kg−1·km−1 and 0.93 ± 0.07 kcal· kg−1· km−1. We found no significant correlations between oxygen and energy cost of running and biomechanical variables and ground reaction forces at either 12 or 20 km· h−1. However, ground contact times were ~10.0% shorter (very large effect) than in previously published literature in elite runners at similar speeds, alongside an 8.9% lower oxygen cost (very large effect). These results provide evidence to hypothesise that the short ground contact times may contribute to the exceptional running economy of Kenyan runners.
Accepted 1 April 2016
Introduction Since the 1970s, running economy has been recognised as a crucial determinant of distance running performance, though it has also been referred to as “relatively ignored in the scientific literature” (Foster & Lucia, 2007). This highlights how poorly the relationships between running economy, training and biomechanical and gait characteristics are understood (Santos-Concejero, Oliván, et al., 2015). Running economy is defined as the steady-state oxygen uptake (VO2) required at a given submaximal velocity (Nummela, Keränen, & Mikkelsson, 2007) or as the energy requirement per unit of distance run (Fletcher, Esau, & Macintosh, 2009). It is influenced by muscle fibre distribution (Bosco et al., 1987), age (Krahenbuhl & Pangrazi, 1983), sex (Bransford, & Howley, 1977) and anthropometric factors (Lucia et al., 2006). Running economy is also influenced by biomechanical variables, largely attributed to gait cycle and ground contact characteristics (Kyröläinen, Belli, & Komi, 2001; Santos-Concejero et al., 2014). Shorter ground contact times (Nummela et al., 2007; SantosConcejero et al., 2013, 2014), lower stride frequencies (Tartaruga et al., 2012), longer swing times, greater stride angles (SantosConcejero et al., 2014) and longer strides (Santos-Concejero et al., 2013, 2014; Tartaruga et al., 2012) have all been related to improved economy in runners ranging in ability from elite to recreational. Ground reaction forces (GRFs) have also been shown to influence economy, with lower peak GRFs associated with improved running economy biomechanical variables, largely
KEYWORDS
Energy cost of running; ground contact; stride length; stride frequency; African runners
attributed to gait cycle and ground contact characteristics (Anderson, 1996; Kyröläinen et al., 2001). Kenyan runners are among the most economical runners in the world (Santos-Concejero, Billaut, et al., 2015), and as a result, numerous researchers have studied whether this factor may enable Kenyan runners’ outstanding performance (Larsen, 2003; Saltin et al., 1995; Tam et al., 2012). Although a dissociation between running economy and performance in Kenyan runners could exist (Mooses, Mooses, et al., 2015), a deep analysis of the running kinematics and energy cost of running in Kenyan runners may provide important insights into the biomechanical determinants of their energy cost of running and thus, performance. One hypothesis is that the exceptional running economy of Kenyan runners may be the result of relatively short ground contact times (Kong & de Heer, 2008). This may be a consequence of a high efficacy in the use of the recoil of elastic energy from the tendinous structures accompanied by shorter stretching and higher stretching to preactivation ratio than has been measured in lesser performers (Sano et al., 2013). This hypothesis has yet to be tested as the exceptional running economy of Kenyan runners has not been explored as an outcome of specific gait cycle and ground contact characteristics in previous studies analysing these parameters (Kong & de Heer, 2008; Sano et al., 2015). Thus, the present study aimed to determine whether spatio-temporal parameters and biomechanical variables of the gait cycle may be associated with running economy in a group
CONTACT J. Santos-Concejero
[email protected] Department of Physical Education and Sport, Faculty of Physical Activity and Sport Sciences, University of the Basque Country UPV/EHU. Portal de Lasarte 71, 01007 Vitoria-Gasteiz, Spain © 2016 Informa UK Limited, trading as Taylor & Francis Group
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of elite Kenyan runners. We hypothesised that East African runners’ exceptional running economy would be associated with shorter ground contact times, lower stride frequencies, longer swing times, longer strides and lower GRFs, in support of previously published literature.
Methods Fifteen elite Kenyan male runners from the Kalenjin tribe (age: 23.7 ± 4.2 years) with mean 10 and 21 km race times of 28.7 ± 0.4 min and 62.2 ± 1.0 min, respectively, were recruited for the study. Of the 25 athletes initially contacted, 10 declined the invitation to participate due to injuries or being focused on main competitions in Europe and America. The Research Ethics Committee of the University of Cape Town approved this study (HREC ref 151/2013), which was conducted post hoc in accordance with the principles of the Declaration of Helsinki (October 2013, Fortaleza). Informed consent was obtained from all individual participants included in the study. All participants were seasoned competitors and were tested between November and May. During this period, they were in peak condition for target competitions of the road season (fall and spring). Forty-eight hours prior to the first test, athletes abstained from hard training sessions and competition. They refrained from alcohol and caffeine ingestion for at least 24 h before testing. All athletes completed a familiarisation session on the treadmill prior to the experimental sessions.
Anthropometry For descriptive purposes, height (cm) and body mass (kg) were recorded using a high precision balance (Seca 899, Seca, Germany) and a stadiometer (Charder HM200P, Charder Electronic Co, Taiwan) and the body mass index (BMI) was calculated. Eight skinfold sites (triceps, biceps, subscapular, supra-iliac, supraspinale, abdominal, front thigh and median calf) were measured in duplicate with skinfold calipers (Holtain Tanner-Whitehouse, Crymych, UK) by the same researcher to the nearest millimetre and body fat percentage was calculated (Yuhasz, 1974). All measurements were taken following the guidelines outlined by the International Society for the Advancement of Kinanthropometry.
Running economy assessment All athletes completed two constant-speed running sets of 6 min each, separated by 5 min recovery periods on a treadmill (H/P/Cosmos Saturn, Nussdorf-Traunstein, Germany) at a gradient of 1%. A slow increase in VO2 during a constant-workrate exercise performed above the lactate threshold has been described, also known as the slow component of the VO2. Thus, to ensure steady-state measurements, the speeds selected, 12 km·h−1, which was tested first (warm-up pace), and 20 km·h−1 (~half-marathon pace), were slower than the individual lactate threshold of each athlete [further confirmed during the test by the respiratory exchange ratio (RER) being below 1.0 during the whole running bout for all athletes]. RER
maximum, minimum and mean values were 0.81, 0.75 and 0.78 at 12 km·h−1 and 0.99, 0.96 and 0.98 at 20 km· h−1. Gas exchange data were collected using an automated breath-by-breath system (COSMED Quark CPET, Rome, Italy), which was calibrated before each session according to the instructions of the manufacturers. Volume calibration was performed at different flow rates with a 3-L calibration syringe (Cosmed, Rome, Italy) allowing an error 0.2 and
