How A Sauna Can Boost Your Running Endurance

Are you looking for a way to boost your athletic performance and endurance without adding more mileage or difficulty to your workouts? Here, the scientific evidence that suggests sitting in a sauna, as well as alternative forms of heat training, can boost your endurance and running capability will be reviewed.

What is a Sauna?

Saunas have long been popular in many European and Asian cultures for their numerous health benefits¹, such as increased circulation and reduced pain. But, for those unfamiliar with saunas, what are they? In general, a sauna is a small room that is designed for wet or dry heat, up to 110^o C (230^o F). Through control of additional parameters such as humidity, the conditions are made more tolerable.

Evidence for Enhanced Endurance

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There are two important studies that have been performed which have provided evidence that saunas can improve athletic performance in athletes.
In the first study, titled Effect of post-exercise sauna bathing on the endurance performance of competitive male runners², physiological adaptations to sauna bathing were observed in six male endurance runners. Each runner underwent three separate, three week long periods of training. Prior to the study, participants were asked to perform a 15 minute treadmill test to exhaustion at the runners’ personal best 5k pace. For the three-week sauna period, the runners sat in a wet sauna at approximately 90^o C for 30 minutes, three times per week, immediately following exercise. In addition to three weeks of sauna sessions, runners completed three weeks of controlled training without the sauna, and a three-week washout period in between.
Following the three-week sauna and three-week control periods, additional treadmill tests were performed as well as plasma, red-cell, and total blood volume measurements. Relative to the control period, athletes were able to increase their time to exhaustion by an average of 32%, enhancing their endurance by approximately 1.9%.
Blood plasma and red-cell volumes showed significant improvements, as they increased an average of 7.1% and 3.5%, respectively, following the three-week sauna period. The scientists concluded that as little as 30 minutes, three times per week in a sauna following exercise can enhance performance, likely due to increased blood volumes.
In a second study, researchers found that athletes who underwent heat training sessions had improved exercise tolerance, particularly in hot conditions. For the study entitled Heat acclimation responses of an ultra-endurance running group preparing for hot desert-based competition³, scientists studied the effect of hyperthermic adaptations on a group of six male ultra-runners. This study was novel in that it specifically addressed sauna in addition to ultra-endurance training loads.
The study participants first completed a pre-acclimation period at 20^o C, followed by three, 2-hour running sessions at 60% VO2max at 30^o C on a treadmill. Those sessions were then followed by three, 2-hour running sessions at 60% VO2max at 35^oC on a treadmill. Additional data such as body mass and blood / urine samples were collected prior to exercise, while rectal temperature, heart rate, thermal comfort rating, and rating of perceived exertion were measured before and during exercise.
Ultimately, similar findings as the aforementioned sauna study were reported, where significant increases in plasma volume were observed following the heated exercise protocol (approximately 7.9% enhancement). While this value is slightly higher than what was observed in the sauna study (7.1% vs. 7.9%), this research suggests that sauna bathing can be nearly as effective as exercising in high temperatures for heat adaptation training.

Evidence for Enhanced Muscle Metabolism

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While sauna use has been shown to enhance overall endurance by improving blood plasma volumes, there is additional research which suggests that sitting in a sauna can provide other benefits as well. For instance, one study suggests that endurance is improved after heat acclimation thanks to enhanced muscle metabolism, which improves aerobic exercise tolerance.
In the study, Muscle metabolism during exercise in the heat in unacclimatized and acclimatized humans⁴, ten male runners were tested for the effect of heat acclimatization on aerobic exercise tolerance. The test subjects were subjected to 8 days of heat acclimatization. Before and after acclimatization of the study, participants performed a heat exercise test that consisted of 6 hours of intermittent submaximal exercises in conditions of 39.7^o C and 31% relative humidity. While the heat exercise test was performed at 50% of maximal oxygen uptake, 45 second cycling sprints at maximal effort were also performed before and after each heat exercise test.
The amount of muscle glycogen utilized during the heat exercise test was lower after heat acclimatization. However, no differences were observed before and after acclimatization for blood glucose, lactate, or respiratory exchange ratios.
Prior to heat acclimatization, which consisted of 90 minutes of daily cycling in the heat for 8 days, participants had a reduced total work output in the 45-second cycling sprint following the heat exercise test. This result was not observed after heat acclimatization. Scientists theorize that reduction in sprint performance following the heat exercise test in unacclimated athletes could be caused by a reduction in muscle pH due to decreased accumulation of lactic acid in the blood.
Therefore, heat acclimatization resulted in a shift in fuel selection during submaximal heat exercise that caused a sparing of muscle glycogen. Ultimately, the less use of muscle glycogen at submaximal effort is associated with the improved ability to perform intense exercise following prolonged heat exertion, which provides evidence for the utility of heat training, such as sauna bathing.
In a second similar study, the ability of athletes to utilize muscle glycogen after heat acclimation was also tested. In Substrate utilization in leg muscle of men after heat acclimation⁵, the effects of heat acclimation on substrate utilization were studied in eight men. As in the previous study, participants were heat acclimated for 8 days via 90-minute cycling sessions in a room heated to 39.6^o C and 29.2% relative humidity. A heat exercise test that comprised 60 minutes of cycling at 50% maximal oxygen consumption was performed before and after the heat acclimation period.
Measurements such as muscle glycogen utilization, respiratory exchange ratio, and calculated rate of carbohydrate oxidation were obtained. In all instances, these measurements were significantly lower during the heat exercise test performed after heat acclimation. Additionally, femoral venous glucose and lactate levels were also lower as a result of heat acclimation.
No changes were observed in plasma free fatty acid, glycerol concentrations, or glucose / lactate / glycerol arteriovenous uptake and release in the heat exercise tests. Free fatty acid uptake increased slightly above resting levels following heat acclimation, and blood flow in the legs was slightly – but significantly – greater following this portion of the study as well. Ultimately, these findings led researchers to conclude that athletes utilize less muscle glycogen following heat acclimation.
For athletes, this result can prolong endurance. Glycogen is the simplest form of energy for an endurance athlete, and sparing its use until the later stages of an event can keep an athlete from hitting the proverbial wall. Although the two studies cited here did not utilize a sauna, the principles of heat acclimation are similar regardless of mode. In fact, a sauna might be a safer option, because it reduces the risk of dangerous dehydration that can occur when exercising in extreme temperatures.

Evidence for Improved Endurance Recovery

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While it might be difficult for people to wrap their heads around sauna – a passive exercise – as a method for improving performance, it certainly isn’t a stretch to say that this favorite Finnish activity is good for recovery. Now, scientists have evidence to support this assertion.
In Effects of far-infrared sauna bathing on recovery from strength and endurance training sessions in men⁶, the effects of far-infrared sauna on exercise recovery were studied. Additionally, the far-infrared sauna was compared to the traditional Finnish sauna. For reference, a far-infrared sauna utilizes a heater to emit light in the far-infrared wavelength to produce radiant heat that is absorbed 3 – 4 cm by skin and fat tissues. A traditional Finnish sauna, on the other hand, is the type of sauna most frequently found in health clubs. This type of sauna is a dry sauna heated by a wood or electric stove.
For this study, ten physically active men participated in either a 60-minute hypertrophic strength training session or a 30 – 40-minute maximal effort endurance training session. Following each type of training, participants spent 30 minutes in a far-infrared sauna at a temperature of 35 – 50^o C with humidity of 25 – 35% or a traditional Finnish sauna of 35 – 50^o C and 60 – 70% humidity. Performance tests were also administered throughout the study which included maximal isometric bench press and leg press, counter movement jump, and a VO2 max test on a treadmill.
Following the strength training sessions, participants displayed decreased maximal isometric strength in bench press, leg press, counter movement jump, and pH. However, heart rate and lactate concentration increased, as expected. During the recovery period no significant differences were observed between participants who sat in a far-infrared sauna and those that did not participate in sauna bathing (the control group).
Additionally, maximal endurance training sessions increased oxygen uptake, heart rate, lactate concentration, and decreased pH, all of which was expected. During recovery, counter movement jump performance was significantly higher after far-infrared sauna bathing than when no sauna was incorporated during recovery. When traditional Finnish sauna and far-infrared sauna were compared, heart rate was higher in traditional Finnish sauna participants (92 + 13 beats/min) than in far-infrared sauna bathers (71 + 7 beats/min).
Ultimately, the researchers concluded that the deep penetration of infrared heat in conjunction with milder temperatures and lower humidity is ideal for promoting the neuromuscular system to recover from maximal endurance activity.

How Should Sauna Bathing be Incorporated into Endurance Training?

The benefits of sauna for endurance athletes are vast. To get the most out of this experience, athletes should utilize the sauna post-workout. While research has suggested that heat training (i.e. exercising in temperatures above 30^o C for extended periods of time) can provide a more significant boost to endurance, doing so can be dangerous for athletes that are pre-disposed to heat stroke, heat intolerance, dehydration, heart disease, or have high blood pressure.
The studies described here indicate that 30-minute sauna sessions can nearly replicate the benefits achieved during heat training, without the potential drawbacks. While a traditional Finnish sauna such as the kind found at health clubs and hotels are beneficial for athletes is most commonly utilized by athletes, infrared saunas are able to more deeply penetrate skin and tissues for enhanced neuromuscular benefits.
To experience the full performance enhancing benefit of heat acclimation, athletes should allow for at least 8 days of continuous sessions, or 2 – 3 weeks of intermittent sessions.

References
1. Hannuksela ML, Ellahham S. Benefits and risks of sauna bathing. Am J Med. 2001;110(2):118-26. Link
2. Scoon GS, Hopkins WG, Mayhew S, Cotter JD. Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. J Sci Med Sport. 2007;10(4):259-62. Link
3. Costa RJ, Crockford MJ, Moore JP, Walsh NP. Heat acclimation responses of an ultra-endurance running group preparing for hot desert-based competition. Eur J Sport Sci. 2014;14 Suppl 1:S131-41. Link
4. King DS, Costill DL, Fink WJ, Hargreaves M, Fielding RA. Muscle metabolism during exercise in the heat in unacclimatized and acclimatized humans. J Appl Physiol. 1985;59(5):1350-4. Link
5. Kirwan JP, Costill DL, Kuipers H, et al. Substrate utilization in leg muscle of men after heat acclimation. J Appl Physiol. 1987;63(1):31-5. Link
6. Mero A, Tornberg J, Mäntykoski M, Puurtinen R. Effects of far-infrared sauna bathing on recovery from strength and endurance training sessions in men. Springerplus. 2015;4:321. Link

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