Page 59 - JSOM Fall 2021

TABLE 2 Baseline Values and Percent Changes at 0 Hours and 24 Hours Compared to Baseline in Performance Variables During the Study
Pre-Test Post 0 Hours (%) Post 24 Hours (%)
Variable (Mean ± SD) (Δ Mean ± SD; CI) Inference (Δ Mean ± SD; CI) Inference
STROOP, s 107 ± 9 7.1 ± 14.0; 11.1 M ↓ –2.6 ± 12.5; 9.1 S uncl ↑
††
Dexterity, s 27.3 ± 6.3 249 ± 83; 173 EL †††† ↓ –4.5 ± 20.3; 14.0 S uncl ↑
PRS 4.2 ± 1.2 0.0 ± 0.0; 0.0 (CI) T 14.4 ± 8.8; 6.9 S**↑
††
Grip right, kg 58 ± 8 –34.1 ± 15.9; 7.7 VL †††† ↓ –6.1 ± 3.2; 2.3 S ↓
Grip left, kg 55 ± 6 –40.6 ± 47.1; 18.3 VL ↓ –4.4 ± 8.6; 6.2 S ↓
††
†
CMJ height, cm 33.2 ± 5.4 –14.4 ± 11.0; 7.1 M ↓ 0.0 ± 6.7; 5.1 T ‡‡
†††
CMJ power, W 3,743 ± 392 –10.9 ± 6.1; 4.1 M ††† –5.7 ± 4.3; 3.1 S ↓
†††
PRS = perceived recovery status, CMJ = counter movement jump.
Trivial (T): < 0.2, small (S): 0.2–0.6; moderate (M): 0.6–1.2; large (L): 1.2–2.0; very large (VL): 2.0–4.0; extremely large (EL): < 4.0.
*Possibly beneficial, **likely beneficial, ***very likely beneficial.
††
†††
† Possibly harmful, likely harmful, very likely harmful, †††† most likely harmful.
‡ Possibly trivial, likely trivial, very likely trivial, ‡‡‡‡ most likely trivial.
‡‡
‡‡‡
uncl Unclear (need more data).
↑ = Better; ↓ = Worse.
TABLE 3 Pre-test, 0 Hours, and 24 Hours Absolute Values in Blood Biomarkers During the Study
Pre-Test Post 0 Hours Post 24 Hours
Variable (Median ± IQR) (Median ± IQR) Inference (Median ± IQR) Inference
CK, U/L 284 ± 132 322 ± 210 M ↑ 314 ± 307 M ↑
†††
†††
Cortisol, nmol/L 659 ± 117 846 ± 120 L †††† ↑ 675 ± 140 T ↓
uncl
CRP, mg/L 5 ± 5 4 ± 5 T ‡‡‡‡ 17 ± 11 M ↑
†††
†
Testosterone, nmol/L 18 ± 6 7 ± 4 VL †††† ↓ 16 ± 4 T ↓
CK = creatine kinase, CRP = C-reactive protein.
Trivial (T): < 0.2, small (S): 0.2–0.6; moderate (M): 0.6–1.2; large (L): 1.2–2.0; very large (VL): 2.0–4.0; extremely large (EL): < 4.0.
*Possibly beneficial, **likely beneficial, ***very likely beneficial.
††
† Possibly harmful, likely harmful, very likely harmful, †††† most likely harmful.
†††
‡‡‡
‡ Possibly trivial, likely trivial, very likely trivial, ‡‡‡‡ most likely trivial.
‡‡
uncl Unclear (need more data).
↑ = Better; ↓ = Worse.
Core and Skin Temperature During the first 15 minutes of the swim, core temperature
The mean core temperature decreased from 37.4 ± 0.3°C to increased in all recruits, indicating elevated heat production
37.0 ± 0.9°C during the swim. When including the after-drop, compared to heat loss. After the initial 15 minutes, the core
core temperature dropped 1.5 ± 0.8°C. An after-drop was temperature was remarkably stable until 150 minutes, when
observed in all test subjects after the swim (green dotted line some recruits started to decline (Figure 2). This finding in-
in Figure 2), with an average drop at –1.1 ± 0.3°C measured dicated well-functioning and properly insulated dry suits,
from the point when the subjects exited the water until the as long as the recruits were able to maintain normal swim-
core temperature was at the lowest after the swim. ming. The drop in core temperature was probably caused by
reduced heat production due to exhaustion. Furthermore,
Figure 2 shows the change in core temperature. During the after the swim, an after-drop was observed in all recruits, al-
exercise, one of the recruits reached a core temperature of though they doffed in heated shelters (Figure 2, green, dotted
34.4°C, which is below the threshold of hypothermia (35°C). lines). This physiological response is important to be aware
Five of the recruits had a core temperature below 36°C during of among operations in cold water. Reductions in skin tem-
the exercise. All lowest core temperature readings were mea- peratures of a similar magnitude have been associated with
sured after the recruits had exited the water. decreased internal muscle temperature, which in turn leads
to decreased muscle force. In our study, lower body power
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The skin temperature increased the first 20 minutes of the was reduced after the swim but normalized at 24 hours. The
swim before it gradually dropped during the last part of the swim was rated moderate (RPE) by the recruits and may in-
swim. The drop in T skin was on average –9.8 ± 3.3°C during dicate that the energy cost was not considerable during the
the exercise (Figure 3). swim.

Maximum voluntary contraction grip strength has been shown
Discussion
to decrease after cold water immersion. One interesting ques-
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The main findings in the present study were the reductions in tion is how much time it takes before grip strength returns
lower body power, reaction time, grip strength, and dexterity to normal. Our study revealed that grip strength was back to
immediately after the swim. After 24 hours, most effects of the near pre-test levels after 24 hours. Therefore, with these novel
swim were small or returned close to the baseline. After the findings, one can speculate that a decrease in skin temperature
swim, CK and cortisol were elevated compared to baseline, may affect performance and could be an essential variable to
while CRP was not changed compared to baseline. consider in addition to core temperature.

Impact of a 10,000-m Cold-Water Swim | 57