Muscle Oxygen Delivery in the Forearm and in the Vastus Lateralis Muscles in Response to Resistance Exercise: A Comparison Between Nepalese Porters and Italian Trekkers

Abstract

Altitude ascending represents an intriguing experimental model reproducing physiological and pathophysiological conditions sharing hypoxemia as the denominator. The aim of the present study was to investigate fractional oxygen extraction and blood dynamics in response to hypobaric hypoxia and to acute resistance exercises, taking into account several factors including different ethnic origin and muscle groups. As part of the "Kanchenjunga Exploration & Physiology" project, six Italian trekkers and six Nepalese porters took part in a high altitude trek in the Himalayas. The measurements were carried out at low (1,450 m) and high altitude (HA; 4,780 m). Near-infrared spectroscopy (NIRS)-derived parameters, i.e., Tot-Hb and tissue saturation index (TSI), were gathered at rest and after bouts of 3-min resistive exercise, both in the quadriceps and in the forearm muscles. TSI decreased with altitude, particularly in forearm muscles (from 66.9 to 57.3%), whereas the decrement was less in the quadriceps (from 62.5 to 57.2%); Nepalese porters were characterized by greater values in thigh TSI than Italian trekkers. Tot-Hb was increased after exercise. At altitude, such increase appeared to be higher in the quadriceps. This effect might be a consequence of the long-term adaptive memory due to the frequent exposures to altitude. Although speculative, we suggest a long-term adaptation of the Nepalese porters due to improved oxygenation of muscles frequently undergoing hypoxic exercise. Muscle structure, individual factors, and altitude exposure time should be taken into account to move on the knowledge of oxygen delivery and utilization at altitude.

Keywords: Himalayas; hemodynamic response; hypobaric hypoxia; near-infrared spectroscopy; resistance exercise.

Figure 1

Altimetric plan of the “Kanchenjunga Exploration & Physiology” project. Measurements refer to near-infrared spectroscopy (NIRS) assessment, both on forearm (handgrip task) and anterior thigh (leg extension task).

Figure 2

Tissue saturation index (TSI) of participants during “Kanchenjunga Exploration & Physiology” project. Measurements were done with a NIRS device on forearm (upper panels) and anterior thigh (lower panels), 3 min before (rest) and 3 min after (recovery) a 3-min-lasting exercise. EX represents the 3-min time spot of resistance exercise, constituted by 18 submaximal contractions. Both groups (Italians and Nepalese) were measured at low (1,450 m, left panels) and high (4,750 m, right panels) altitude. Data represent single values with mean ± SD, averaged by 1-min recording.

Figure 3

Total hemoglobin (tot-HB) of participants during “Kanchenjunga Exploration & Physiology” project. Measurements were done with a NIRS device on forearm (upper panels) and anterior thigh (lower panels), 3 min before (rest) and 3 min after (recovery) a 3-min-lasting exercise. Exercise (EX) represents the 3-min time spot of resistance exercise, constituted by 18 submaximal contractions. Both groups (Italians and Nepalese) were measured at low (1,450 m, left panels) and high (4,750 m, right panels) altitude. Data represent single values with mean ± SD, averaged by 1-min recording.