International Journal of Sports Physiology and Performance, 2015, 10, 381-387 http://dx.doi.org/10.1123/ijspp.2014-0179 © 2015 Human Kinetics, Inc.
www.IJSPP-Journal.com ORIGINAL INVESTIGATION
Gait-Cycle Characteristics and Running Economy in Elite Eritrean and European Runners Jordan Santos-Concejero, Jesús Oliván, José L. Maté-Muñoz, Carlos Muniesa, Marta Montil, Ross Tucker, and Alejandro Lucia Purpose: This study aimed to determine whether biomechanical characteristics such as ground-contact time, swing time, and stride length and frequency contribute to the exceptional running economy of East African runners. Methods: Seventeen elite long-distance runners (9 Eritrean, 8 European) performed an incremental maximal running test and 3 submaximal running bouts at 17, 19, and 21 km/h. During the tests, gas-exchange parameters were measured to determine maximal oxygen uptake (VO2max) and running economy (RE). In addition, ground-contact time, swing time, stride length, and stride frequency were measured. Results: The European runners had higher VO2max values than the Eritrean runners (77.2 ± 5.2 vs 73.5 ± 6.0 mL · kg–1 · min–1, P = .011, effect sizes [ES] = 0.65), although Eritrean runners were more economical at 19 km/h (191.4 ± 10.4 vs 205.9 ± 13.3 mL · kg–1 · min–1, P = .026, ES = 1.21). There were no differences between groups for ground-contact time, swing time, stride length, or stride frequency at any speed. Swing time was associated with running economy at 21 km/h in the Eritrean runners (r = .71, P = .033), but no other significant association was found between RE and biomechanical variables. Finally, best 10-km performance was significantly correlated with RE (r = –.57; P = .013). Conclusions: Eritrean runners have superior RE compared with elite European runners. This appears to offset their inferior VO2max. However, the current data suggest that their better RE does not have a biomechanical basis. Other factors, not measured in the current study, may contribute to this RE advantage. Keywords: performance, ground contact, stride length, stride frequency, African runners Among the factors that may explain the remarkable longdistance running success of East African athletes, running economy (RE), commonly defined as the steady-state oxygen uptake (VO2) required at a given submaximal speed, has garnered the most attention over the last 2 decades.1–3 In this regard, the RE values reported by Lucia et al3 in Eritrean runners (average of ~190 mL · kg–1 · min–1) are among the lowest reported in the literature. A favorable RE is the result of a complex interaction of factors that lead to efficient muscle work and a fast and effective running gait.4 In the case of East African runners, exceptional RE has been attributed to structural and anthropometric characteristics including smaller calf circumference1,3 and optimized gastro-Achilles-tendon characteristics that allow an improved use of the recoil elastic energy.5 However, RE can be also largely influenced by biomechanical variables related to ground-contact and stride characteristics.6,7 Small vertical oscillations,8 longer strides and higher frequencies,7,9 shorter ground-contact and longer swing times,10 and lower groundreaction forces11 have been related to an improved RE. East African runners have been reported to have relatively short ground-contact times compared with elite European runners.12 They have also been found to have faster leg swing through a greater range than performance matched Japanese elite runners.13 Santos-Concejero and Tucker are with the Dept of Human Biology, University of Cape Town, Cape Town, South Africa. Oliván, Muniesa, Montil, and Lucia are with the Dept of Morphological Sciences, European University of Madrid, Madrid, Spain. Maté-Muñoz is with the Dept of Sport Sciences, Alfonso X El Sabio University, Villanueva de la Cañada, Spain. Address author correspondence to Jordan Santos-Concejero at jordan. [email protected].
These observations suggest that biomechanical factors may contribute to the superior RE and, therefore, the success of East African runners. However, no study has analyzed the influence of biomechanical variables on RE in runners of East African origin. Thus, this study aimed to determine whether biomechanical characteristics such as ground-contact time, swing time, stride length, and stride frequency contribute to exceptional East African running economy, thus advancing the theories for their distance-running success. We studied this question in Eritrean runners, who have been reported to be among the most economical runners worldwide.3
Methods Subjects Seventeen elite long-distance runners (9 Eritrean, 8 European) with a 10-km race-time range of 26 minutes 36 seconds to 29 minutes 48 seconds participated in the study. Mean ± SD ages were 23.3 ± 4.8 years for the Eritreans and 28.0 ± 4.2 years for the Europeans. The local institutional review board approved this study, which was performed in accordance with the principles of the Declaration of Helsinki 2013. All athletes were informed about all the tests and possible risks involved and provided a written informed consent before testing. All participants were currently competing and were tested in February to March while they were in their peak condition for the target competitions of the cross-country season. Before being tested in our laboratory (~600 m altitude), the Eritreans lived and trained in Europe for 1 week (at sea level) and in Madrid (~600 m altitude) for another week. Athletes were excluded if they were not actively participating in races, had a recent 10-km best performance slower than 30 minutes, or suffered any illness or injury within 381
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382 Santos-Concejero et al
the 3 months before testing. Athletes reported their recent 10-km best performance and a detailed training history, the latter being confirmed by their respective coaches. All Eritrean athletes belonged to the Eritrea’s main ethnic group, the Tigrigna, which forms about half of the population of the country, and are descendants of parents of the same ethnic group. All of them were moderate-altitude natives born and raised in the high central plateau of the country (altitude varying from 1800 to 3000 m), and they were all descendants of moderate-altitude natives. European runners were all Spaniards of the same ethnic and geographic origin (mainly from Castile, the main, central plateau of Spain, altitude ~600 m). They have always lived and trained in Castile and have only occasionally attended altitudetraining camps. None of them had trained or lived at moderate or high altitude in the months before the study, and none of them had previously used a hypoxic tent to simulate altitude exposure during sleeping hours. Twenty-four hours before testing, athletes were encouraged to abstain from hard training sessions and competition to be well rested. They were also asked to maintain their precompetition diets throughout the test procedures and to refrain from alcohol and caffeine ingestion for at least 24 hours before testing. All athletes had previous experience with treadmill running, including a thorough familiarization session with the treadmill used in this study.
Design The design of the study was that of observational research.
Methodology Anthropometry. For descriptive purposes, height (cm) and body mass (kg) were recorded and body-mass index (in kg/m2) was calculated. Six skinfold sites (triceps, subscapular, suprailiac, abdominal, front thigh, and median calf) were measured in triplicate with skinfold calipers (Holtain, Crymych, UK) by the same researcher to the nearest millimeter. Total-leg, thigh, and shank length, as well as maximal thigh and calf circumferences, were measured. All measurements were taken as detailed elsewhere.14 Exercise Tests. All participants completed 2 tests on 2 consecutive
days: a maximal incremental test for VO2max determination and constant-speed bouts for RE and biomechanical-characteristics determination. The maximal incremental running test was performed at 1% slope on a treadmill (Technogym Run Race 1400 HC, Gambettola, Italy) and began at 11 km/h after a self-selected general previous warm-up. The speed was increased by 0.5 km/h every 30 seconds until volitional exhaustion. The treadmill was calibrated using a measuring wheel (Trumeter Measure Meter, Manchester, UK) with a measurement error 0.2 and
www.IJSPP-Journal.com ORIGINAL INVESTIGATION
Gait-Cycle Characteristics and Running Economy in Elite Eritrean and European Runners Jordan Santos-Concejero, Jesús Oliván, José L. Maté-Muñoz, Carlos Muniesa, Marta Montil, Ross Tucker, and Alejandro Lucia Purpose: This study aimed to determine whether biomechanical characteristics such as ground-contact time, swing time, and stride length and frequency contribute to the exceptional running economy of East African runners. Methods: Seventeen elite long-distance runners (9 Eritrean, 8 European) performed an incremental maximal running test and 3 submaximal running bouts at 17, 19, and 21 km/h. During the tests, gas-exchange parameters were measured to determine maximal oxygen uptake (VO2max) and running economy (RE). In addition, ground-contact time, swing time, stride length, and stride frequency were measured. Results: The European runners had higher VO2max values than the Eritrean runners (77.2 ± 5.2 vs 73.5 ± 6.0 mL · kg–1 · min–1, P = .011, effect sizes [ES] = 0.65), although Eritrean runners were more economical at 19 km/h (191.4 ± 10.4 vs 205.9 ± 13.3 mL · kg–1 · min–1, P = .026, ES = 1.21). There were no differences between groups for ground-contact time, swing time, stride length, or stride frequency at any speed. Swing time was associated with running economy at 21 km/h in the Eritrean runners (r = .71, P = .033), but no other significant association was found between RE and biomechanical variables. Finally, best 10-km performance was significantly correlated with RE (r = –.57; P = .013). Conclusions: Eritrean runners have superior RE compared with elite European runners. This appears to offset their inferior VO2max. However, the current data suggest that their better RE does not have a biomechanical basis. Other factors, not measured in the current study, may contribute to this RE advantage. Keywords: performance, ground contact, stride length, stride frequency, African runners Among the factors that may explain the remarkable longdistance running success of East African athletes, running economy (RE), commonly defined as the steady-state oxygen uptake (VO2) required at a given submaximal speed, has garnered the most attention over the last 2 decades.1–3 In this regard, the RE values reported by Lucia et al3 in Eritrean runners (average of ~190 mL · kg–1 · min–1) are among the lowest reported in the literature. A favorable RE is the result of a complex interaction of factors that lead to efficient muscle work and a fast and effective running gait.4 In the case of East African runners, exceptional RE has been attributed to structural and anthropometric characteristics including smaller calf circumference1,3 and optimized gastro-Achilles-tendon characteristics that allow an improved use of the recoil elastic energy.5 However, RE can be also largely influenced by biomechanical variables related to ground-contact and stride characteristics.6,7 Small vertical oscillations,8 longer strides and higher frequencies,7,9 shorter ground-contact and longer swing times,10 and lower groundreaction forces11 have been related to an improved RE. East African runners have been reported to have relatively short ground-contact times compared with elite European runners.12 They have also been found to have faster leg swing through a greater range than performance matched Japanese elite runners.13 Santos-Concejero and Tucker are with the Dept of Human Biology, University of Cape Town, Cape Town, South Africa. Oliván, Muniesa, Montil, and Lucia are with the Dept of Morphological Sciences, European University of Madrid, Madrid, Spain. Maté-Muñoz is with the Dept of Sport Sciences, Alfonso X El Sabio University, Villanueva de la Cañada, Spain. Address author correspondence to Jordan Santos-Concejero at jordan. [email protected].
These observations suggest that biomechanical factors may contribute to the superior RE and, therefore, the success of East African runners. However, no study has analyzed the influence of biomechanical variables on RE in runners of East African origin. Thus, this study aimed to determine whether biomechanical characteristics such as ground-contact time, swing time, stride length, and stride frequency contribute to exceptional East African running economy, thus advancing the theories for their distance-running success. We studied this question in Eritrean runners, who have been reported to be among the most economical runners worldwide.3
Methods Subjects Seventeen elite long-distance runners (9 Eritrean, 8 European) with a 10-km race-time range of 26 minutes 36 seconds to 29 minutes 48 seconds participated in the study. Mean ± SD ages were 23.3 ± 4.8 years for the Eritreans and 28.0 ± 4.2 years for the Europeans. The local institutional review board approved this study, which was performed in accordance with the principles of the Declaration of Helsinki 2013. All athletes were informed about all the tests and possible risks involved and provided a written informed consent before testing. All participants were currently competing and were tested in February to March while they were in their peak condition for the target competitions of the cross-country season. Before being tested in our laboratory (~600 m altitude), the Eritreans lived and trained in Europe for 1 week (at sea level) and in Madrid (~600 m altitude) for another week. Athletes were excluded if they were not actively participating in races, had a recent 10-km best performance slower than 30 minutes, or suffered any illness or injury within 381
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382 Santos-Concejero et al
the 3 months before testing. Athletes reported their recent 10-km best performance and a detailed training history, the latter being confirmed by their respective coaches. All Eritrean athletes belonged to the Eritrea’s main ethnic group, the Tigrigna, which forms about half of the population of the country, and are descendants of parents of the same ethnic group. All of them were moderate-altitude natives born and raised in the high central plateau of the country (altitude varying from 1800 to 3000 m), and they were all descendants of moderate-altitude natives. European runners were all Spaniards of the same ethnic and geographic origin (mainly from Castile, the main, central plateau of Spain, altitude ~600 m). They have always lived and trained in Castile and have only occasionally attended altitudetraining camps. None of them had trained or lived at moderate or high altitude in the months before the study, and none of them had previously used a hypoxic tent to simulate altitude exposure during sleeping hours. Twenty-four hours before testing, athletes were encouraged to abstain from hard training sessions and competition to be well rested. They were also asked to maintain their precompetition diets throughout the test procedures and to refrain from alcohol and caffeine ingestion for at least 24 hours before testing. All athletes had previous experience with treadmill running, including a thorough familiarization session with the treadmill used in this study.
Design The design of the study was that of observational research.
Methodology Anthropometry. For descriptive purposes, height (cm) and body mass (kg) were recorded and body-mass index (in kg/m2) was calculated. Six skinfold sites (triceps, subscapular, suprailiac, abdominal, front thigh, and median calf) were measured in triplicate with skinfold calipers (Holtain, Crymych, UK) by the same researcher to the nearest millimeter. Total-leg, thigh, and shank length, as well as maximal thigh and calf circumferences, were measured. All measurements were taken as detailed elsewhere.14 Exercise Tests. All participants completed 2 tests on 2 consecutive
days: a maximal incremental test for VO2max determination and constant-speed bouts for RE and biomechanical-characteristics determination. The maximal incremental running test was performed at 1% slope on a treadmill (Technogym Run Race 1400 HC, Gambettola, Italy) and began at 11 km/h after a self-selected general previous warm-up. The speed was increased by 0.5 km/h every 30 seconds until volitional exhaustion. The treadmill was calibrated using a measuring wheel (Trumeter Measure Meter, Manchester, UK) with a measurement error 0.2 and
