Study under review: Cross Acclimation between Heat and Hypoxia: Heat Acclimation Improves Cellular Tolerance and Exercise Performance in Acute Normobaric Hypoxia
All exercise causes stress, which is followed by adaptations that allow the body to better handle that stress in the future. Environmental conditions, such as extreme temperatures or changes in altitude, or even humidity, can also cause stress and adaptation. Recent research has shown that adaptation to one type of stressor can induce protective responses upon exposure to a different stressor, presuming they share common adaptive responses. When improved cellular protection or reduced physiological strain is observed in an organism in response to a different type of stressor, it is referred to as cross-tolerance. Some examples of possible cross-tolerance from rat experiments are shown in Figure 1.
Adapted from: Fregly MJ.Compr Physiol. 2011.
Changes associated with heat acclimation include an increased cardiac output and plasma volume, an earlier onset of sweating with an increased sweat rate (and more diluted sweat), lower core temperature at rest and during exercise (reduced thermoregulatory strain) and a lower heart rate for a given workload during exercise (reduced cardiovascular strain). Hypoxic exposure refers to a state of reduced oxygen availability, experienced when traveling to high altitudes or simulated in a lab. Responses to hypoxia include an increase in red blood cells and oxygen-carrying capacity, as well as adaptations for improving carbohydrate metabolism.
At the cellular level, both heat and hypoxic stress stimulate the heat shock response. Heat shock proteins (HSPs) refer to a large family of proteins that aid in a cell’s response to physical stress. These proteins are important because they are observed in species across the animal kingdom. The most commonly studied HSPs expressed in response to heat or hypoxia are the HSP70 and HSP90 families, which are named after their molecular weight. In addition to HSPs, increases in hypoxia-inducible factor 1-α (HIF1-α), the master regulator of oxygen-regulated genes, have also been observed in animals after heat stress and heat acclimation. This suggests an association, and potential interaction, between HIF-1α and HSPs during heat acclimation.
Previous research using exposure to heat and hypoxia (alone and in combination) has shown reductions in physiological strain (measured by the heat shock response) during subsequent hypoxic exercise. Human studies have yet to examine the HIF-1α response to heat acclimation, which may play a role in the improved performance seen during hypoxic exercise after heat acclimation. Accordingly, the goal of this new study was to examine the effects of heat or hypoxic acclimation on physiological, cellular, and performance responses to hypoxic exercise in humans.
Other Articles in Issue #19 (May 2016)
The art & science of evidence-based practice and elite performance By Craig Pickering
As one of the rare athletes to participate in both the Summer and Winter Olympic Games, Craig has a unique perspective on the intersection of optimal performance and evidence-based practice.
Relaxing arteries with magnesium
To stave off cardiovascular disease, we want our arteries to be more pliable than stiff. This trial tested six months of magnesium supplementation for the purpose of reducing arterial stiffness.
Beating “the burn” with baking soda
Can you believe that something as simple as baking soda may boost performance? While this fact has been known for a while, researchers didn’t know that people’s responses to different doses can vary quite a bit
A compound from beer may help fat loss
Bitter, hop-derived compounds found in beer may actually reduce body fat levels. Previously only shown in mice, this study tested the theory in humans
Sugar is the ultimate antioxidant and insulin will make you younger: Appreciating a few poorly recognized but critical contributions of carbohydrate
By Chris Masterjohn, PhD: Sugar is widely demonized in the media and medical establishment. Professor Masterjohn provides an eye-opening and detailed view on some potential protective roles of glucose.
Milk gone bad: A1 beta-casein and GI distress
Casein isn’t just the slowly digesting protein that helps prevent muscle breakdown. This study looked at possible negative effects of the most common type of casein in milk
Arsenic in rice: big trouble for little infants?
Depending on where it’s grown, rice can have rather high levels of arsenic. Especially brown rice. This may be important for developing infants
How much protein does grandpa really need?
One of the many downsides to aging is altered protein mechanics. Based on the theory that protein requirements for seniors may be pegged too low, this study quantified protein needs in older males.
Is resistance exercise the next frontier for nitrates?
Nitrate use for athletics has exploded in the past few years, but research typically focuses on aerobic activities like longer-distance cycling or swimming. Could nitrates also show benefit for weightlifting?