THE EFFECT OF A COLD ENVIRONMENT ON HUMAN PERFORMANCE
Juha Oksa Ph.D. Finnish Institute of Occupational Health, Oulu, Centre of Expertise
for Health and Work Ability, Physical Work Capacity team
When humans are exposed to cold ambient temperatures cooling may occur, and even
while exercising, when body heat production is increased, this may result in subnormal
It is well verified that subnormal body and especially muscle
temperature has an adverse effect on neuromuscular and physical performance capacity
The following mini review will focus on the effects of cooling on dynamic
exercise, functional properties of the muscles and some neural aspects of muscle
In general, the ability to perform dynamic exercises is more readily disturbed by
cooling than isometric exercise. The decrement in performance is usually expressed
as absolute decrease (%) or related to decrease in muscle temperature (% • °C-1
decrease in muscle temperature).
Regardless of the exercise type, duration or component
of performance (endurance, velocity, force etc.) decrease in dynamic performance
after cooling is in the order of 2 - 10 % • °C-1 decrease in muscle temperature
(4, 19). However, even bigger values have been reported. Bergh and Ekblom (3) found
that cooling produced a 55 % decrement in maximal working time while muscle temperature
was decreased by 3.4 °C, corresponding to 16 % • °C-1 decrease in muscle temperature.
Also, Oksa et al. (15) found that during drop jump exercise the highest decrease
in performance was 17 % • °C-1. The latter implies that exercise type, which is
very fast and efficiently utilises the elastic properties of the working muscles
is espe¬cially susceptible for cooling.
Another important factor which needs to
be taken into account is that maximal performance capacity (e.g. force and endurance,
12, 13) decreases due to cooling but the energy cost and motor unit recruitment
during submaximal exercise is higher (13, 14).
This results in higher relative strain
of a given work in cold environment as compared with thermoneutral environment.
Dose – response relationship
A dose – response relationship between muscle temperature and performance can be
found as exemplified in Figure 1.
Whether the muscle is passively cooled or actively
rewarmed after cooling is of no importance; the predominant factor in determining
the outcome of physical performance is muscle temperature (15). Figure 1.
between muscle temperature and performance. Transversally within the muscle there
is a temperature gradient the steepness of which is dependent on severity of cold
For example, exposing the bare forearm to 5 °C still air for 120
minutes induces a gradient in m.
flexor carpi radialis where muscle temperature
from the warmer core decreases 0.5 °C for each 0.5 cm towards the shell of the muscle
There are individual differences in physical characteristics, which may modify the
thermal responses to cooling and protect against loss of performance. First, subcutaneous
fat acts as a thermal insulator slowing the rate of cooling (9).
Second, with increasing
body size the surface area - body mass ratio decreases thus decreasing the area
for heat loss and along with the increase in body size the body heat content also
increases. Due to these factors increased body size slows the rate of cooling (6).
Third, a fit person is able to produce more heat than unfit, therefore maintaining
thermal balance more effectively (10). All these factors may help to maintain performance
capacity in cold environment.
On the other hand, with subjects matched for fitness
level and amount of subcutaneous fat but differing with the amount of muscle mass
(normal vs. muscular subjects) it was observed that substantial amount of muscle
mass after passive cooling does not seem to protect against loss of performance
The functional properties of skeletal muscle
In addition to decreased physical performance cooling has also a profound effect
on func¬tional properties of skeletal muscle (8). It has been well verified that
the rate of tension development in the beginning of muscle contraction i.e. the
time to maximum force level (twitch or tetanic tension) is temperature dependent
The temperature sensitivity (Q10) of the rate of tension development
in humans has been shown to be approximately 1.5 (17). A similar temperature dependence
has been found also for the rate of relaxation at the end of muscle contraction
The Q10 of the rate of relaxation in humans has been reported to be approximately
between 1.7 - 2.3 (20) The velocity of muscle contraction itself, shortening and
lengthening, is also slower in a given time when muscle tissue is cooled (8). Therefore,
the power production of the muscle during shortening is less and power absorption
during lengthening is more thus leading to a less powerful contraction of a muscle.
Cooling also slows nerve and muscle conduction velocity, which may result in a slower
and weaker muscle contraction (5, 7). The decrease in conduction velocity has been
reported to have a Q10 of approximately 1.4 (11) and absolute decrease in nerve
conduction velocity has been reported to vary between 1.1 - 2.4 m • s-1/°C (7).
Force production is regulated peripherally and/or centrally. Peripheral regulation
is mainly conducted through reflex pathways, the stretch reflex (T-reflex) playing
a major role. Many studies concerning the effects of cooling on stretch reflex have
shown that cooling suppresses stretch reflex amplitude (e.g. 7).
There is evidence
that the suppressed T-reflex ampli¬tude is due to decreased activity of the muscle
spindles and thus decreased gammamotoneuron excitability (1) and these changes may
lead to a decreased force production of a muscle (16). On the other hand, it also
has been shown that during low-intensity repetitive work in cold. (when forearm
muscle strain is higher in relation to same work in thermoneutral condition), stretch
reflex responses are being enhanced in relation to thermoneutral responses.
probably indicates that the increased strain of the working muscles were met by
increas¬ing the reflex activity, therefore, in cold recruiting more muscle fibres
in order to maintain the given work level (14).
It is evident that cooling deteriorates physical performance, its components, functional
pro¬perties of the muscle and neural functioning. The amount of deterioration is
dependent on the amount of cooling i.e. how much muscle temperature is lowered.
There seems to be no "threshold" in muscle temperature after which performance starts
to decrease, after the decrement starts immediately when muscle temperature decreases.
While maximal working capacity is lowered and submaximal work requires increased
fibre recruitment the relative strain for a given athletic performance in cold weather
can be higher. Since already peripheral and very superficial cooling is sufficient
to decrease performance capacity this needs to be taken into account (e.g. to increase
heat loss during exercise: do not expose working muscles to cold air) while designing
exercise regimes in cold and especially when preparing for athletic competitions.
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