The Impact Of Fluid Restriction On Neuromuscular And Cognitive Performance During A Ruck March

The loads carried by tactical athletes (TA) can increase thermal stress and induce dehydration, negatively impacting performance and mission outcomes. Yet, these factors are rarely studied together during tactical maneuvers such as a ruck march (RM). PURPOSE: To assess effects of RM on hydration, neuromuscular (NM) and cognitive (COG) performance. METHODS: 12 adults with RM experience volunteered for the study (m = 7, f = 5, age = 33.3 ± 6.5 yrs, height = 173.1 ± 8.0 cm, mass = 78.7 ± 16.7 kg, VO2max = 47.6 ± 7.4 ml/kg/min, body fat =17.3 ± 5.6%). Participants completed a 9.65-km RM with a 20-kg ruck sack on a treadmill at 4.83-km/h in a temperature-controlled laboratory (22.2 degrees C). No water intake was allowed during the RM. Hydration and performance were tested at pre-, mid-, and post-RM time points. Hydration was tested via Urine Specific Gravity (USG) and changes in body mass (BM). NM performance was tested via vertical countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) on force plates sampling at 1000 Hz. COG performance was assessed via psychomotor vigilance task reaction time. Wilcoxon signed ranks tests with a Bonferroni correction examined changes between time points (a priori alpha<0.05). Wilcox effect sizes (ES) were calculated. RESULTS: The RM induced dehydration according to significantly increased USG from pre-to mid(ES = 0.770), mid-to post(ES = 0.883), and pre-to post-RM(ES = 0.883), as well as significantly decreased BM from pre-to mid(ES = 0.828), mid-to post(ES = 0.873), and pre-to post-RM(ES = 0.873). Only CMJ landing impulse (IMP) increased from pre-to post-RM (ES = 0.72). No other significant differences in NM or COG performance were observed. CONCLUSIONS: A RM in a controlled environment induced dehydration but, unexpectedly, had little effect on NM or COG performance. The increased landing IMP suggests altered landing mechanics, a potential injury risk factor, when fatigued and dehydrated. The greater landing IMP at post-RM, but not mid-RM, indicates that the magnitude of IMP change may be relative to the distance of a RM. Future research should determine if a training intervention can alleviate the negative impacts of a RM on landing IMP.