RTX cooling, or Rapid Thermal Exchange, started with two Stanford researchers in the 90s looking at rewarming patients after surgery. The basis is that mammals have arteriovenous anastamoses in the palms and soles, and this can be used to bring high volumes of blood in contact with a thermal plate. A small vacuum is created in the device to further increase blood flow. The inventors received a DARPA grant to study the device for possible military use. It came into vogue in the athletic and wilderness fields as an easy and effective way to decrease or increase core temperature. A secondary benefit of increased endurance was noticed in some trials, and this is being looked at by a few. Currently devices are in use by many sports teams, including the San Francisco 49ers.
The curious thing is, if you look through the 9 studies available on pubmed using palm cooling as the search, you’ll notice not all of them are positive.
The positive studies are authored by:
- Kwon, Robergs, Mermier, Schneider, Gurney, 2013 (Oddly positive for increased performance with cooling AND heating over neutral, n=8)
- Grahn, Cao, Nguyen, Liu, Heller, 2012 (core temperatures reduced and work volumes increased, n=8)
- Kwon, Roberts, Kravitz, Gurney, Mermier, Schnieder, 2010 (Cooling outperformed heating and neutral, core temperatures lower, n=16)
- Grahn, Cao, Heller, 2005 (Cooling increased exercise duration [n=18] and decreased core temp [n=8])
- Hsu, Hagioban, Jacobs, Attallah, Friedlander, 2005 (cooling decreased tympanic temp, lactate, and VO2 [n=8] as well as increased performance [n=8])
The negative studies are authored by:
- Scheadler, Saunders, Hanson, Devor, 2013 (Time to exhaustion reduced including warmup time, no significant core temp change, n=12)
- Amorim, Yamada, Robergs, Schneider, 2010 (no slowing of hyperthermia, outperformed by water perfusion vest, n=10)
- Walker, Zupan, McGregor, Cantwell, Norris, 2009 (no change in temp, heart rate, or VO2, n=10)
- Kuennen, Gillum, Amorim, Kwon, Schneider, 2009 (core temp decrease of 0.35 degrees C, less effective than cold water immersion of liquid cooling garments, n=10)
Certainly sample size in all of these is low, and perhaps the device is effective at cooling and/or endurance increase. However, based on the literature available, it is 5 in favor, 4 against. Then consider that 2 of the 5 positive papers are written by the owners of the patent for the device (Grahn and Heller). I would wait to purchase one of these devices for my personal gym.
Tech shirts. All of the major companies make them now. Mostly polyester, they were designed originally to increase evaporation to provide a “cool” feeling and decrease the amount of sweat present in the clothing after a workout. They were popular with military in the Middle East until they were banned due to the injuries they cause when burned. Living in south Texas, I’m infinitely familiar with clothing soaked with sweat.
This article took 3 different kinds of synthetic shirts and 1 ordinary cotton shirt (Fruit of the Loom!) and compared them. The methods section makes me never want to be friends with these guys, as they made them start at 7 kph, going up 1kph per minute up to 14 kph. Then inclination was increased by 1 degree per minute until exhaustion. This was to determine peak oxygen uptake. Then for each individual fabric test they made them perform at 70% of that maximum uptake for 30 minutes, then increased the inclination to exhaustion again. At least there was a fan blowing on them from the front. Temperature was controlled at 31.7C and relative humidity was kept at 42%.
During testing, they measured
- Temperatures (ambient, skin, body, and core)
- Relative humidity (ambient, chest, and back)
- Blood lactate (from the ear)
- Ratings of
- perceived exertion on a 6-20 scale
- thermal sensation on a 1-9 scale
- wettedness sensation on a 1-4 scale
- shivering and sweating sensation on a 1-7 scale
- Heart rate
- Respiratory exchange ratio
- Oxygen uptake
They found that 2 of the 3 synthetic shirts did lower body temperatures, decreased relative humidity, and made the runners “feel cooler” during exercise. They did not demonstrate any increase in performance ability. Thus, it is likely that this kind of shirt may make you feel less wet, but is unlikely to make you an Olympic athlete right out of the box. Certainly they aren’t worth a huge premium over regular shirts.
Exercising in a Hot Environment: Which T-shirt to Wear?