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LOAD CARRYING IN NEPALESE PORTERS AND IN CAUCASIAN MOUNTAINEERS
Presentation 0739, Locomotion. 11:00, Room 101B
S380
LOAD CARRYING IN NEPALESE PORTERS AND IN CAUCASIAN MOUNTAINEERS A.E. Minetti1, L.P. Ardigò2, F. Formenti3, L.A. Peyrè-Tartaruga1 and D. Susta4 1 Institute of Human Physiology, University of Milano, Italy 2 Faculty of Exercise and Sport Science, University of Verona, Italy 3 Department of Physiology, Oxford, UK 4 CEBISM, University of Trento, Italy email: [email protected] INTRODUCTION During our first expedition to the Himalayan region [1], we found that Nepalese porters carry huge loads uphill in hypoxia at a much higher (60%) speed than Caucasian mountaineers, with a lower mass specific cost of transport. We concluded that their performance was partially explained by a better cardiorespiratory conditioning related to an improved abituation to high altitude. Nepalese porters’ heart beat frequency was higher than in Caucasian at all the investigated altitudes. While this finding explained the higher metabolic and mechanical power, the much better economy of transport was more difficult to justify. By measuring at 100 Hz the tilt of the trunk+load segment during the ascending and descending portions of the path, we noticed that a more ample and variable oscillation was associated to the Caucasian load carrying. Thus we inferred that the Nepalese porters’ skill could consist in a smaller coactivation of muscles involved in balancing the most loaded segment of the body. On September 2006 we repeated our expedition to Nepal to extend our study. The idea was to check a sort of ‘EMGcost’ of locomotion and to compare muscular activity within subjects (at different imposed loads) and between Napalese and Caucasian subjects. METHODS Five Nepalese porters and 5 Caucasian Mountaineers have been tested in the field experiments. They were asked to walk uphill and downhill along a monotonic path (gradient 22%) without any extra load and while carrying 40 kg of stones in their doko/rucksack, in Namche-Bazar at 3500 m asl. Subjects were instrumented with a portable EMG recording device (PocketEMG, BTS, Milano, Italy) and 14 electrodes located both on postural and propulsive muscles of one side of the body. They also carried a GPS (Edge, Garmin, USA) and a portable metabograph (k4b2, COSMED, Rome, Italy) equipped with a heart monitor. The mean EMG activity was obtained by integrating the signal over the entire test, then by adjusting for skin thickness and for individual muscle volume.
Journal of Biomechanics 40(S2)
RESULTS AND DISCUSSION The ascension speed and the cost of transport in the loaded condition confirmed our original data [1]. The same variables reported no difference between Nepalese porters and Caucasian mountaineer when the subjects walked uphill and downhill unloaded. In the loaded condition, mean EMG amplitude (summation/duration) of individual muscles was similar in Nepalese and Caucasian subject, but when expressed per unit distance the average value is much higher in Caucasian mountaineers. No clear trend was found in the comparison of individual muscle activity in the loaded/unloaded condition (no difference also between postural and propulsive muscles). CONCLUSIONS From these results we can say that when unloaded there is no difference between Caucasian mountaineers and Nepalese porters. While loaded, a higher overall muscle activation is needed by Caucasian to carry 40 kg load. It is possible that the much lower walking speed of Caucasian subjects, imposed by a worse cardio-respiratory adaptation, also causes impaired efficiency and economy due to intrinsic muscle characteristics (i.e. a very low contraction speed in the efficiency/speed diagram). REFERENCES 1. Minetti AE, et al. Proceedings of Royal Society B, 273: 2791- 2797, 2006. ACKNOWLEDGEMENTS This study was carried out within the framework of the EvK2-CNR “Scientific and Technological Research in Himalaya and Karakorum” Project, in collaboration with the Royal Nepal Academy of Science and Technology (RONAST) as foreseen by the Memorandum of Understanding between the Government of the Kingdom of Nepal and the Government of the Republic of Italy. We are also grateful to Cosmed S.r.l. (Rome, Italy) and BTS (Milano) for supporting logistic and instrumentation aspects.
XXI ISB Congress, Podium Sessions, Wednesday 4 July 2007
S380
LOAD CARRYING IN NEPALESE PORTERS AND IN CAUCASIAN MOUNTAINEERS A.E. Minetti1, L.P. Ardigò2, F. Formenti3, L.A. Peyrè-Tartaruga1 and D. Susta4 1 Institute of Human Physiology, University of Milano, Italy 2 Faculty of Exercise and Sport Science, University of Verona, Italy 3 Department of Physiology, Oxford, UK 4 CEBISM, University of Trento, Italy email: [email protected] INTRODUCTION During our first expedition to the Himalayan region [1], we found that Nepalese porters carry huge loads uphill in hypoxia at a much higher (60%) speed than Caucasian mountaineers, with a lower mass specific cost of transport. We concluded that their performance was partially explained by a better cardiorespiratory conditioning related to an improved abituation to high altitude. Nepalese porters’ heart beat frequency was higher than in Caucasian at all the investigated altitudes. While this finding explained the higher metabolic and mechanical power, the much better economy of transport was more difficult to justify. By measuring at 100 Hz the tilt of the trunk+load segment during the ascending and descending portions of the path, we noticed that a more ample and variable oscillation was associated to the Caucasian load carrying. Thus we inferred that the Nepalese porters’ skill could consist in a smaller coactivation of muscles involved in balancing the most loaded segment of the body. On September 2006 we repeated our expedition to Nepal to extend our study. The idea was to check a sort of ‘EMGcost’ of locomotion and to compare muscular activity within subjects (at different imposed loads) and between Napalese and Caucasian subjects. METHODS Five Nepalese porters and 5 Caucasian Mountaineers have been tested in the field experiments. They were asked to walk uphill and downhill along a monotonic path (gradient 22%) without any extra load and while carrying 40 kg of stones in their doko/rucksack, in Namche-Bazar at 3500 m asl. Subjects were instrumented with a portable EMG recording device (PocketEMG, BTS, Milano, Italy) and 14 electrodes located both on postural and propulsive muscles of one side of the body. They also carried a GPS (Edge, Garmin, USA) and a portable metabograph (k4b2, COSMED, Rome, Italy) equipped with a heart monitor. The mean EMG activity was obtained by integrating the signal over the entire test, then by adjusting for skin thickness and for individual muscle volume.
Journal of Biomechanics 40(S2)
RESULTS AND DISCUSSION The ascension speed and the cost of transport in the loaded condition confirmed our original data [1]. The same variables reported no difference between Nepalese porters and Caucasian mountaineer when the subjects walked uphill and downhill unloaded. In the loaded condition, mean EMG amplitude (summation/duration) of individual muscles was similar in Nepalese and Caucasian subject, but when expressed per unit distance the average value is much higher in Caucasian mountaineers. No clear trend was found in the comparison of individual muscle activity in the loaded/unloaded condition (no difference also between postural and propulsive muscles). CONCLUSIONS From these results we can say that when unloaded there is no difference between Caucasian mountaineers and Nepalese porters. While loaded, a higher overall muscle activation is needed by Caucasian to carry 40 kg load. It is possible that the much lower walking speed of Caucasian subjects, imposed by a worse cardio-respiratory adaptation, also causes impaired efficiency and economy due to intrinsic muscle characteristics (i.e. a very low contraction speed in the efficiency/speed diagram). REFERENCES 1. Minetti AE, et al. Proceedings of Royal Society B, 273: 2791- 2797, 2006. ACKNOWLEDGEMENTS This study was carried out within the framework of the EvK2-CNR “Scientific and Technological Research in Himalaya and Karakorum” Project, in collaboration with the Royal Nepal Academy of Science and Technology (RONAST) as foreseen by the Memorandum of Understanding between the Government of the Kingdom of Nepal and the Government of the Republic of Italy. We are also grateful to Cosmed S.r.l. (Rome, Italy) and BTS (Milano) for supporting logistic and instrumentation aspects.
XXI ISB Congress, Podium Sessions, Wednesday 4 July 2007