Breath-hold diving has been traditionally practiced for professional and recreational reasons and has recently emerged as a competitive sport. The physiological response during breath-holding, also known as diving response, consists mainly of bradycardia and peripheral vasoconstriction. Elite apneists can suppress the urge to breathe, sustain greater arterial desaturation and develop pronounced bradycardia, thus accomplishing impressively long breath-hold times. This study explored physiological responses during static apnea and their association with apnea duration in breath-hold divers with high physiological adaptations acquired from long-term apnea training. Nine well-trained competitive divers held their breath for as long as possible while floating motionlessly in a swimming pool (26–27 °C), simulating an actual “static apnea competition”. Long apnea durations (302 ± 60 s) as well as severe oxygen desaturation (minSaO₂ 46 ± 11%) and bradycardia (minHR 49 ± 8 bpm) were achieved. Apnea duration was positively correlated with forced vital capacity (r = 0.771) and apnea duration until initiation of desaturation (r = 0.736) and negatively correlated with minSaO₂ (r = −0.672) (p < 0.05). Moreover, minHR during apnea was correlated with pre-apneic hemoglobin concentration (r = 0.685) (p < 0.05). The prolonged apnea durations achieved by the well-trained divers in this study, while performing maximum immersed static apnea under competitive simulated conditions, were related to their high lung volumes and their delayed and profound O₂ desaturation, whereas their bradycardic response was not a decisive factor.

Purpose: We have previously observed substantially higher oxygen uptake in soldiers walking on terrain at night than when performing the same walk in bright daylight. The aims of the present study were to investigate the influence of vision on mechanical efficiency during slow, horizontal, constant-speed walking, and to determine whether any vision influence is modified by load carriage. Methods: Each subject (n = 15) walked (3.3 km/h) for 10 min on a treadmill in four different conditions: (1) full vision, no carried load, (2) no vision, no carried load, (3) full vision with a 25.5-kg rucksack, (4) no vision with a 25.5-kg rucksack. Results: Oxygen uptake was 0.94 ± 0.12 l/min in condition (1), 1.15 ± 0.20 l/min in (2), 1.15 ± 0.12 l/min in (3) and 1.35 ± 0.19 l/min in (4). Thus, lack of vision increased oxygen uptake by about 19%. Analyses of movement pattern, by use of optical markers attached to the limbs and torso, revealed considerably shorter step length (12 and 10%) in the no vision (2 and 4) than full vision conditions (1 and 3). No vision conditions (2 and 4) increased step width by 6 and 6%, and increased vertical foot clearance by 20 and 16% compared to full vision conditions (1 and 3). Conclusion: The results suggest that vision has a marked influence on mechanical efficiency even during entrained, repetitive movements performed on an obstacle-free horizontal surface under highly predictable conditions.

The aim of this study was to investigate the effect of prolonged steady state swimming with a wetsuit, on thermoregulatory and behavioural responses, in water of 25°C. Ten male swimmers participated in two 75-min swim trials, in one wearing a neoprene wetsuit (WS), and the other a conventional swimsuit (SS). The swimming intensity was controlled at 70% of swimmers’ critical velocity (CV). Core (Tcore) and skin (Tsk) temperature, heart rate (HR), and behavioural modulators, were measured before, during and after swimming. A 2-way ANOVA for repeated measures with aFisher’s 2SD test was used for multiple comparisons and a paired t-test with a Tukey post hoc analysis for pre and post measurements at p< 0.05. The results demonstrated an interaction of Tcore (p = 0.039), between time in the water and type of garment worn. Tcore with the WS initially increased until the 45^th min and plateaued, while with the SS was continuously decreasing. HR was lower during swimming with the WS and higher with the SS. Thermal sensation and thermal comfort, were more favourable with the WS (p < 0.05). Thus, WS use during prolonged swimming, helped maintain Tcore levels, and improved thermal perceptions, at 25 °C.

Uniformed services commonly perform foot-borne operations at night, while using visual aid in terms of night vision goggles (NVG). During slow-level walking, complete lack of visual input alters kinematics and markedly increases the metabolic demand, whereas the effect on kinematics and energy expenditure of restricting the peripheral visual field by wearing NVG is still unknown. The purpose was to evaluate whether metabolic demands and kinematics during level walking are affected by complete darkness with and without visual aid. Eleven healthy men walked on a treadmill (inclination: +2.3°, velocity: 4 km/h) with full vision in a lighted laboratory (Light), and in complete darkness wearing either a blindfold (Dark), or restricting the visual field to about 40° by wearing monocular (Mono) or binocular (Bino) NVG. Oxygen uptake (⁠|$\dot{\text{V}}$|O₂) was measured to evaluate metabolic demands. Inertial measurement units were used to estimate kinematics, and the outcome was validated by using a motion capture system. Ratings of perceived exertion, discomfort, and mental stress were evaluated after each condition using a Borg ratio scale. Physiologic and kinematic variables were evaluated using repeated measures analysis of variance (ANOVA), whereas ratings were evaluated using non-parametric Friedman ANOVA. |$\dot{\text{V}}$|O₂ was 20% higher in the Dark (1.2 ± 0.2 L/min) than the Light (1.0 ± 0.2 L/min) condition. Nominally, |$\dot{\text{V}}$|O₂ in the Mono (1.1 ± 0.2 L/min) and Bino (1.1 ± 0.2 L/min) conditions fell in between those in the Light and Dark conditions but was not statistically different from either the Light or the Dark condition. Step length was shorter in the Dark (−9%, 1.22 ± 0.16 m) and Mono (−6%, 1.27 ± 0.09 m) conditions than in the Light condition (1.35 ± 0.11 m), whereas the Bino (1.28 ± 0.08 m) condition was not statistically different from either the Light or the Dark condition. The three conditions with no or limited vision were perceived more physically demanding, more uncomfortable, and more mentally stressful than the Light condition, and the Dark condition was perceived more mentally stressful than both NVG conditions. The study confirms that complete lack of visual cues markedly reduces the mechanical efficiency during level walking, even under obstacle-free and highly predictable conditions. That |$\dot{\text{V}}$|O₂ and step length values for the NVG conditions fell in between those of the Light and Dark conditions suggest that both foveal and peripheral vision may play important roles in optimizing the mechanical efficiency during level walking.

A im : To explore the effect of a combat swimming training program (CSTP), with and without equipment, on swimming performance. Material & Method : 45 male army officer cadets volunteered to participate in the study and were randomly divided into three groups: a control group (CG) and two experimental groups. The experimental groups participated in a 4-week combat swimming training program with equipment (CSTPE) or without equipment (CSTPS). Prior to and after the CSTP, all groups performed a 400-m and a 4 × 50-m swimming task, and the time to complete the task, peak blood lactate, and peak heart rate were measured. Results : The time to complete the 400-m and 4 × 50-m trials improved significantly only in the CSTPE group (490 ± 66 s pre and 463 ± 50 s post for 400 m; and 205 ± 28 s pre and 192 ± 19 s post for 4 × 50 m; p < 0.05), while the CG and CTSPS groups did not improve their time significantly in either trial. All groups presented similar peak lactate and peak heart rate values. Conclusions : The results suggest that only the CSTPE group improved swimming performance in both the 400-m and 4 × 50-m trials.