Reductions in systemic and skeletal muscle blood flow and oxygen delivery limit maximal aerobic capacity in humans

[EN] BACKGROUND: A classic, unresolved physiological question is whether central cardiorespiratory and/or local skeletal muscle circulatory factors limit maximal aerobic capacity (VO2max) in humans. Severe heat stress drastically reduces VO2max, but the mechanisms have never been studied. METHODS AND RESULTS: To determine the main contributing factor that limits VO2max with and without heat stress, we measured hemodynamics in 8 healthy males performing intense upright cycling exercise until exhaustion starting with either high or normal skin and core temperatures (+10 degrees C and +1 degrees C). Heat stress reduced VO2max, 2-legged VO2, and time to fatigue by 0.4+/-0.1 L/min (8%), 0.5+/-0.2 L/min (11%), and 2.2+/-0.4 minutes (28%), respectively (all P<0.05), despite heart rate and core temperature reaching similar peak values. However, before exhaustion in both heat stress and normal conditions, cardiac output, leg blood flow, mean arterial pressure, and systemic and leg O2 delivery declined significantly (all 5% to 11%, P<0.05), yet arterial O2 content and leg vascular conductance remained unchanged. Despite increasing leg O2 extraction, leg VO2 declined 5% to 6% before exhaustion in both heat stress and normal conditions, accompanied by enhanced muscle lactate accumulation and ATP and creatine phosphate hydrolysis. CONCLUSIONS: These results demonstrate that in trained humans, severe heat stress reduces VO2max by accelerating the declines in cardiac output and mean arterial pressure that lead to decrements in exercising muscle blood flow, O2 delivery, and O2 uptake. Furthermore, the impaired systemic and skeletal muscle aerobic capacity that precedes fatigue with or without heat stress is largely related to the failure of the heart to maintain cardiac output and O2 delivery to locomotive muscle.

Percepción de los residentes de Las Palmas de Gran Canaria ante el turismo de cruceros

[ES] El turismo de cruceros ha reaparecido con fuerza desde los años ochenta, acelerándose su implantación en Europa -y en particular en Canarias-, desde la siguiente década. Gran parte de los estudios sobre el turismo de cruceros se han centrado en las características de la demanda (el perfil del turista, la capacidad de gasto, los impactos que causa, etc.). Sin embargo, la literatura sobre la percepción que tienen los residentes sobre este turismo es más bien escasa y donde se centra el actual estudio, en particular en el espacio más inmediato al Puerto de La Luz y de Las Palmas.[EN] Cruise tourism is a way of taking leisure time in our society. It is an activity that has become very popular since the eighties, accelerating its presence in Europe and, particularly,in the Canary Islands since the following decade. Many of the studies on cruise tourism have focused on the characteristics of the demand (including the profile of tourists, spending power, the impacts that this activity causes, etc.). However, the literature on the residents’ perception about this tourism where this study focuses on, is rather scarce is rather scarce, particularly in the space immediately to the Port of La Luz and Las Palmas.