The influence of backpack chest straps on physiological and performance variables associated with simulated road marching
Hollins, Jana Elizabeth
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This study compared physiological and performance variables during heavy load carriage while wearing an armored vest under a standard issue military backpack using three different chest strap conditions (no chest strap, NCS; standard chest strap, SCS; modified chest strap, MCS). Twenty subjects, all right-handed shooters, completed 4 laboratory visits. The subjects filled out paperwork, received consumables for the next visit, and performed a handgrip strength test during the first visit. The following 3 visits were testing visits with 2 treadmill walking trials per visit at a fixed speed (80.5 m/min) and grade (2%). Each testing visit corresponded to 1 of 3 conditions (NCS, SCS, or MCS) and included a baseline trial carrying only a training rifle (3.3 kg) followed by a pack trial wearing an armored vest, pack, and rifle (47 kg total). Heart rate (HR, bpm), relative oxygen consumption (RVO 2, ml/kg/min), minute ventilation (V E, L/min), and breathing frequency (BF, breaths/min) were measured. Circumferences (bicep, C B, and forearm, C F, cm) and blood lactate (BL, mmol/L) were assessed once per trial on the non-trigger finger arm, while two-point discrimination (mm) was assessed once on the back of the trigger finger hand. Rating of perceived discomfort (RPD), fingertip oxygen saturation (SpO 2, %), and stride rate (SR, stride/min) were assessed twice each trial. Maximum handgrip strength was assessed in each hand simultaneously (HG right and left, kg) two times per trial. All variables were assessed using multivariate 2-factor RM ANOVA and Scheffe's post hoc test (alpha = 0.05). Baselines for all variables were similar. Pack trial means for HR, RVO 2, V E, and BF were higher than baseline but no difference between strap conditions. Fingertip SpO 2 was lower during pack trials than baseline. There were no differences in V T, BL, or left HG between conditions. NCS resulted in greater C F and C B than baseline with C F also being greater than MCS. Right HG was greater for MCS than baselines and NCS. Right and left HG increased 2 minutes post walking. MCS and SCS provided the least evidence for negatively affecting physiologic and performance outcomes, whereas NCS provides the most evidence for negatively affecting outcomes.