Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation

European Journal of Applied Physiology https://doi.org/10.1007/s00421-018-3869-0 ORIGINAL ARTICLE Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation Michail E. Keramidas1 · Magnus Gadefors2 · Lars‑Ove Nilsson2 · Ola Eiken1 Received: 11 January 2018 / Accepted: 16 April 2018 © The Author(s) 2018 Abstract Purpose The study examined the effects of short-term field-based military training with partial sleep deprivation on wholebody endurance performance in well-trained individuals. Methods Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT65), followed by an exhaustive constant-load trial at 85% of PPO (CLT85). Physiological [oxygen uptake (V̇ O2), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise. Results SUSOPS reduced time to exhaustion in C LT85 by 29.1% (p = 0.01). During the C LT65 trial, SUSOPS potentiated the exercise-induced elevations in V̇ O2 and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT85 trials, CO tended to decline (p ≤ 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT65, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT85 trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01). Conclusions The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity. Keywords Autonomic dysfunction · Cerebral oxygenation · Effort · Fatigue · Motivation · Muscle oxygenation Abbreviations CI Confidence interval CLT65 A 15-min constant-load trial at 65% of peak power output CLT85 Exhaustive constant-load trial at 85% of peak power output CO Cardiac output CON Control trial DAP Diastolic arterial pressure FAS Perceived activation Communicated by Phillip D Chilibeck. * Michail E. Keramidas 1 Department of Environmental Physiology, Swedish Aerospace Physiology Center, Royal Institute of TechnologyKTH, Berzelius väg 13, 171 65 Solna, Sweden 2 Military Academy Karlberg, Stockholm, Sweden fR Respiratory frequency FS Affective valence HR Heart rate [La] Blood lactate concentration MAP Mean arterial pressure MFI Multidimensional Fatigue Inventory NIRS Near-infrared spectroscopy PETCO2 Partial pressure of end-tidal carbon dioxide POMS-SF Profile of Mood States-Short Form PPO Peak power output RER Respiratory exchange ratio RPE Ratings for perceived exertion SAP Systolic arterial pressure SD Standard deviation SUSOPS Sustained operations SV Stroke volume TOI Tissue oxygen index V̇ E Expired ventilation V̇ E/V̇ CO2 Ventilatory equivalent for carbon dioxide 13 Vol.:(0123456789) European Journal of Applied Physiology V̇ E/O2 Ventilatory equivalent for oxygen V̇ CO2 Carbon dioxide production V̇ O2 Oxygen uptake V̇ O2peak Peak oxygen uptake VT Tidal volume Δ[HbO2] Changes in oxyhaemoglobin Δ[HbO2] Changes in deoxyhaemoglobin Introduction Military and emergency-response personnel are often required to perform sustained and demanding work in environmental extremes, while provisions for full recovery are limited. During such multi-day tasks, individuals may be exposed to several behavioural stressors, including physical and mental exertion, partial or total sleep deprivation, and caloric deficit (i.e., energy intake is lower than expenditure), which, independently or interactively, might result in functional impairments (for reviews, see Henning et al. 2011; Vrijkotte et al. 2016; Montain and Young 2003). Specifically, military-based studies have suggested that a prolonged period of sustained operations (SUSOPS) degrades cognitive and physical performance; thus, aerobic work capacity is typically suppressed (Guezennec et al. 1994; Nindl et al. 2002). Physiological and psychological modifications, such as low energy substrate availability (Smith et al. 2016; Rognum et al. 1981), muscle-mass loss (Johnson et al. 1994), hypovolemia and/or hypohydration (Lieberman et al. 2005; Wittels et al. 1996), functional peripheral deteriorations (e.g., impaired mitochondrial efficiency; Fernstrom et al. 2007), and decreased motivation and enhanced effort perception (Lucas et al. 2009; Lieberman et al. 2005, 2006), have been regarded as potential determinants of physical performance in such multi-stressor conditions. The SUSOPS effect on endurance capacity seems to be dictated primarily by the severity of energy and sleep deprivation encountered. For instance, short-term (≤ 10 days) periods of low-to-moderate hypocaloria cause minimal, if at all, change in aerobic capacity (Dohm et al. 1986; Knapik et al. 1987; Guezennec et al. 1994). Friedl (1995) has argued that body mass losses of at least 5–10% might be required to adversely affect performance. Moreover, although it is well established that partial sleep deprivation deteriorates cognitive and mental performance, its impact on endurance capacity is equivocal; a few studies have observed an impairment, while others have shown no change (for review, see Fullagar et al. 2015). Hence, information is scarce regarding effects of a short-term SUSOPS, during which the intensities of the stressors are moderate, on aerobic capacity. The purpose of the present study, therefore, was to determine whether, and to what extent, a brief period of 13 multi-stressor military training would influence high-intensity, whole-body, endurance exercise in well-trained individuals. For this purpose, central and peripheral haemodynamics, and perceptual and affective reactions were monitored during exhaustive constant-load cycle ergometry before and immediately after a 2-day SUSOPS with partial sleep deprivation. We hypothesized that, despite its short duration and relatively moderate intensity, SUSOPS would increase cardiorespiratory and psychological strain, thereby precipitating a reduction in maximal exercise tolerance. Methods Ethics approval The experimental protocol was approved by the Human Ethics Committee of Stockholm (2017/1:8), and conformed to the standards set by the Declaration of Helsinki. The study was part of the course “Applied Physical Training Theory for Warfare” of the school program of the Military Academy Karlberg (Sweden). Subjects were informed in detail about the experimental procedures, and gave their consent. Subjects Fo (...truncated)