Page 34 - JSOM Spring 2025

At time 4, the BD-control group (mean 38.56 [SD .39]) had group did not differ as a function of condition (Wilcoxon
higher core temperatures relative to the control-BD group signed rank tests, all Ps>.07). Thermal sensations were lower
(mean 37.95 [SD .41]; Welch’s t (15.63) =3.36, P=.004). At time 5, at time point 1 in the control condition (median –2 [IQR
the BD- control group (mean 38.5 [SD .35]) continued to have 1.25]) relative to the BD condition (median 1 [IQR 1.25]) for
higher temperatures temps relative to the control-BD group the control-BD group (P=.021). No other differences were sig-
(mean 37.93 [SD .49]; Welch’s t (17.85) =3.09, P=.006). For the nificant (all Ps>.07).
order × condition interaction, the BD-control group showed
similar core temperatures during the BD condition (mean 38.1 RPE
[SD .62]) relative to the control condition (mean 38.3 [SD The CLMM (random intercept only) showed no main effects
.47], t (19) =2.34, P=.03 corrected); in contrast, the control-BD or interaction effects for any term(s) (all Zs<1.53; Ps>.1); Fig-
group showed higher core temperatures in the BD condition ure 4.
(mean 37.9 [SD .46]) relative to the control condition (mean
37.7 [SD .47], t =2.79, P=.009). FIGURE 4 Mean (SD) rating of perceived exertion (RPE) responses
(29)
to ruck marching without (CON) and with blood donation (BD)
The LMM showed a significant effect of hand temperatures plotted over the route. Participants rated increased levels of exertion
(random intercepts and slopes of condition) increasing a func- from ruck marching, but RPE was not different between CON
and BD.
tion of time (b=1.86 [SE .39], P<.002) and significant with-
in-subject effect of condition with hand temperatures in the
control condition (mean 25.5 [SD 3.78) being overall higher
relative to the BD condition (mean 23.2 [SD 3.78]; t (49) =3.52,
P<.001). Like core temperatures, there were significant order
× time (P<.001) and order × condition (P=.006) interactions.
Hand temperatures collapsed across condition increased and
were similar across the order groups at times 1, 2, 3, and 4
(Welch’s ts<1.47, Ps>.1 corrected).

At time 5, the BD-control group (mean 26.15 [SD 2.82]) had
higher hand temperatures relative to the control-BD group
(mean 23.04 [SD 3.93]; Welch’s t (17.82) =2.07, P=.053) but the
difference was not significant after correction. For the order
× condition interaction, the BD-control group showed lower
hand temperatures during the BD condition (mean 21.9 [SD
3.91]) relative to the control condition (mean 27.5 [SD 2.58],
t (19) =6.7, P<.001), whereas the control-BD group showed sim- Discussion
ilar hand temperatures in the BD condition (mean 24.0 [SD
4.13]) relative to the control condition (mean 24.2 [SD 3.49], The aim of the present study was to evaluate the impact of com-
t =.21, P>.1). bined altitude exposure, blood donation, and ruck marching on
(29)
physical performance outcomes in acclimatized military person-
Respiration nel. Given the known acute changes in physiology associated
14
For respiration rate (random intercepts), no main effects or with ascending to higher elevations, we hypothesized that
interactions were significant (all Ps>.1). For minute ventila- compromising oxygen-carrying capacity through BD would
tion, the LMM (random intercepts and slopes of condition and limit donors’ military-specific physical performance. Specifi-
time) showed a significant effect of minute ventilation overall cally, we hypothesized that BD would exacerbate physiologi-
decreasing as a function of time (b=–9.17 [SE 6.27], P<.001). cal and perceptual responses, prolong participants’ ruck march
All other terms were not significant (all Ps>.1). time, and increase the magnitude of AMS symptoms during
ruck marching. However, similar outcomes for BD and control
AMS for nearly all measurements suggest that a single unit BD does
Given the overwhelming lack of AMS symptoms reported by not impact ruck march performance or increase the incidence of
participants, there were errors in trying to analyze too many AMS symptoms when performed at elevations up to 3,050m in
“zero” responses, and the ordinal mixed effects models could acclimatized personnel. We did observe increased HR, RPE, and
not distinguish parameters even with the simplest random ef- body temperature as a function of uphill rucking, but these were
fects structure. There were very minor reports of fatigue and not different between BD and control conditions.
dizziness during rucking.
To our knowledge, warfighter performance in high-altitude
Thermal Sensation environments immediately following BD has not been inves-
The CLMM (random intercepts and slopes of condition and tigated. However, parallels in related work may offer insight
time points) showed a significant main effect of order, with into our findings. For example, no decrements in submax-
thermal sensation being overall higher in the control-BD imal exercise performance (performed at sea level 2hr after
group (b=4.53; Z=3.06, P=.002) and thermal sensations in- BD) were observed with cycling intensities up to 170bpm HR,
creasing with time point (b=.66; Z=2.06, P=.039). Further- yet a 6% reduction in aerobic capacity was observed during
more, there was a significant order × condition interaction maximal exercise (also performed 2hr after BD). Additionally,
7
(Z=3.14; P=.002) and order × condition × time point inter- graded treadmill tests performed within 2 hours following a
action (Z=2.19, P=.028). Patterns of results for the three-way 500mL BD at sea level also resulted in no differences in time
15
interaction show that thermal sensation for the BD-control to reach HRs of 180bpm between the sham and BD groups.
32 | JSOM Volume 25, Edition 1 / Spring 2025