NATA Heat Stress Guidelines

The National Athletic Trainers’ Association (NATA) has played an active role in heat illness prevention. In June 2003 NATA published a Consensus Statement on Exertional Heat-Related Illnesses. This document and ancillary documents can be obtained at http://www.nata.org/pfiles/links/heatillness2.htm, or open the .pdf file.

Central to their recommendations were the American College of Sports Medicine guidelines for long distance running (available in Heat Stress Adviser on the Non-Football Guidelines page) and the work of Tasha Kulka and Larry Kenney. Kulka and Kenney's full-text article describing their environmental chamber testing of various football ensembles is available free online at http://www.physsportsmed.com/issues/2002/07_02/kenny.htm . The essence of the Kulka and Kenny football uniform study is outlined below.

Uncompensable heat stress is encountered in the following conditions:

Full football uniform:

For Dry Bulb (DB) temperatures>60°F, any relative humidity (RH)>52.9%; any Dry Bulb temperature>98°F. For Dry Bulb temperatures between 80°F and 98°F, there is a maximum relative humidity for each temperature, and a relative humidity above that level is uncompensable:

The threshold relative humidity at which heat stress becomes non-sustainable is described by this equation: RH=(-75620+(3455*(DB))+(59.15*(DB^2))+(0.45*(DB^3))+(0.001284*(DB^4)))+22.80698

For football uniform with shorts instead of padded pants, the Relative Humidity at which heat stress becomes uncompensable is: defined by this equation: RH=((-0.0523*(DB^2))+(7.2018*DB)-170.42

For T-shirt and shorts, the Relative Humidity at which heat stress becomes uncompensable is: defined by the equation: RH=(-3.9611*DB)+442.06

These standards were devised by observations of exercise in an environmental chamber, and do not include substantial radiant heat (sunlight) effects. For that reason, the author prefers use of the Tulsa Guidelines.

These standards apply for sustained exercise at 35% of MVO2max. For most football linemen, this is the equivalent of Bruce Protocol Stage 1 exercise, which is walking on a treadmill at 1.7mph at a 10% grade. This is the equivalent of 5 metabolic units (METS). 1 MET is equivalent to the amount of energy expended per minute at rest. Fit young adults can sustain 10 METS in a T-shirt and shorts in cool conditions. Top marathon runners routinely achieve close to 20 METS.