Page 60 - JSOM Fall 2021

FIGURE 2 Change in core temperature
compared to baseline during the swim (full
purple line) and the first 45 minutes after
the swim (dotted green line).

FIGURE 3 Skin temperature plotted
individually for the swim (purple line),
and approximately 10 minutes after
exiting the water (dotted green line).

Although the recruits were swimming in a dry suit, and 5-mm elicited high cortisol and low testosterone levels in line with pre-
five-finger Neoprene gloves, manual dexterity declined by vious studies. 5,19 We also observed an increase in CK after stren-
nearly 250% during the swim. Studies have concluded that uous exercise, which is likewise in line with previous studies. 20,21
immersions of the hand in cold water for as short as 5 minutes Surprisingly, and of notable interest, was the clear increase in
results in impairment in both gross and fine manual dexter- CK despite the recruits not performing a typical weight-bearing
ity. It is worth noting that our study subjects were in the activity, as investigated in previous studies. It is possible that
16
water for an average of 258 minutes, and we observed a clear there is increased muscle damage in the legs due to the recruits
gradual reduction in T skin on the forearm (Figure 2). The blood propelling their motion with the use of fins. To our knowledge,
flow to the hands responds rapidly upon cold, inducing vaso- muscle cooling or decreased core temperature does not increase
constriction, which leads to decreased temperature in the fin- CK levels. Therefore, this finding should be investigated further.
gers and hands. Due to the nature of the exercise, we were not
able to measure skin temperature in the fingers of the recruits. The CRP levels were within normal ranges after the swim
but elevated at 24 hours. Similar results are observed after
The large decrease observed in manual dexterity may be detri- long-distance racing, in which the CRP plasma values were
mental for operators as their ability to perform mission tasks, elevated the day after. 21
such as using weapon or operating emergency equipment,
17
could be seriously impaired. Following the immediate im- The recruits used fins to propel their 10,000-m swim. In gen-
pairment, ongoing cold exposure and vasoconstriction have eral terms, large and stiff fins are more energy demanding but
several other adverse potential outcomes, such as non- freezing increase the maximal propulsion per kick. Smaller and more
cold injuries from decreased blood flow. These injuries can flexible fins improve the economy of swimming at more sub-
22
lead to necrosis, immersion foot or frostbite. Therefore pre- maximal speeds. Zamparo et al. showed that the use of fins
18
venting decreased T skin and dexterity are vital. decreases the energy cost by around 50% when compared to
flutter kick without fin. They further elucidated that kick fre-
In the present study, we induced two main stressors to the quency should be decreased as much as possible to reduce the
study subjects, cold water and demanding physical activity, that energy cost.

58 | JSOM Volume 21, Edition 3 / Fall 2021