Assessing injury risk in male and female Royal Navy recruits: does the Functional Movement Screen provide understanding to inform effective injury mitigation?

INTRODUCTION: Musculoskeletal injuries (MSKIs) are common during military and other occupational physical training programmes, and employers have a duty of care to mitigate this injury risk. MSKIs account for a high number of working days lost during initial military training, contribute to training attrition and impact training costs. Poorer movement quality may be associated with increased MSKI risk. METHODS: The present study evaluated the relationship between the Functional Movement Screen (FMS) Score, as a measure of movement quality, and injury risk in Royal Navy (RN) recruits. A cohort of 957 recruits was assessed using the FMS prior to the 10-week phase I training programme. Injury occurrence, time, type and severity were recorded prospectively during the training period. RESULTS: Total FMS Score was associated with injury risk (p≤0.001), where recruits scoring ≥13 were 2.6 times more likely to sustain an injury during training. However, FMS Score accounted for only 10% of the variance in injury risk (R2=0.1). Sex was the only additional variable to significantly affect the regression model. Mean FMS Scores for men (14.6±2.3) and women (14.4±2.4) were similar, but injury occurrence in women was 1.7 times greater than in men. Examining the influence of individual FMS movement tests on injury prediction did not improve the model, where those movements that significantly contributed to injury prediction only accounted for a small amount of the variance (R2=0.01). CONCLUSION: There was a weak relationship between FMS and injury risk in RN recruits. Evidence is provided that FMS score alone would not be appropriate to use as an injury prediction tool in military recruits.

Procedure for assessing patients referred to the UK's military Heat Illness Clinic: a case series.

INTRODUCTION: The UK military operates a Heat Illness Clinic (HIC) to aid the return to exercise, training and occupational duty recommendations for individuals who have suffered exertional heat illness or heatstroke. This paper describes the process of assessment and reports representative data from n=22 patients referred to the HIC. METHOD: The assessment included clinical consultation, and measurement of maximal oxygen consumption (V̇O2max) and a heat tolerance test (HTT) conducted on a treadmill in an environmental chamber with an air temperature of 34°C and 44% relative humidity. Patients began the HTT wearing military clothing, carrying a rucksack (mass 15 kg) and walking at 60% V̇O2max, at 30 min the rucksack and jacket were removed and the T-shirt at 45 min, individuals continued walking for 60-90 min. Patients were considered heat tolerant if rectal temperature achieved a plateau. RESULTS: N=14 patients were heat tolerant on the first assessment and of the n=8 patients required to return for repeat assessment, five were heat tolerant on the second assessment and the remaining three on the third assessment. CONCLUSIONS: In conjunction with patient history and clinical evaluation, the HTT provides a physiological basis to assist with decisions concerning patient management and return to duty following an episode of heat illness.

Staphylococcus aureus colonization and acquisition of skin and soft tissue infection among Royal Marines recruits: a prospective cohort study.

OBJECTIVES: Skin and soft tissue infections (SSTIs) are a serious health issue for military personnel. Of particular importance are those caused by methicillin-resistant Staphylococcus aureus and Panton-Valentine leucocidin (PVL)-positive S. aureus (PVL-SA), as they have been associated with outbreaks of SSTIs. A prospective observational study was conducted in Royal Marine (RM) recruits to investigate the prevalence of PVL-SA carriage and any association with SSTIs. METHODS: A total of 1012 RM recruits were followed through a 32-week training programme, with nose and throat swabs obtained at weeks 1, 6, 15 and 32. S. aureus isolates were characterized by antibiotic susceptibility testing, spa typing, presence of mecA/C and PVL genes. Retrospective review of the clinical notes for SSTI acquisition was conducted. RESULTS: S. aureus colonization decreased from Week 1 to Week 32 (41% to 26%, p < 0.0001). Of 1168 S. aureus isolates, three out of 1168 (0.3%) were MRSA and ten out of 1168 (0.9%) PVL-positive (all MSSA) and 169 out of 1168 (14.5%) were resistant to clindamycin. Isolates showed genetic diversity with 238 different spa types associated with 25 multi-locus sequence type (MLST) clonal complexes. SSTIs were seen in 35% (351/989) of recruits with 3 training days lost per recruit. SSTI acquisition rate was reduced amongst persistent carriers (p < 0.0283). CONCLUSIONS: Nose and throat carriage of MRSA and PVL-SA was low among recruits, despite a high incidence of SSTIs being reported, particularly cellulitis. Carriage strains were predominantly MSSA with a marked diversity of genotypes. Persistent nose and/or throat carriage was not associated with SSTI acquisition. Putative person-to-person transmission within troops was identified based on spa typing requiring further research to confirm and explore potential transmission routes.

Altered forefoot function following a military training activity.

BACKGROUND: Injury rates are high in populations that regularly undertake weight-bearing physical activity, particularly military populations. Military training activities, that often include load carriage, have been associated with lower limb injury occurrence, specifically stress fractures. RESEARCH QUESTION: Recent work identified plantar loading variables as risk factors for lower limb stress fractures in Royal Marines recruits that were assessed during barefoot running. This study aimed to quantify how those plantar loading variables changed in Royal Marines recruits following a prolonged military load carriage activity, to further understand potential mechanisms for lower limb stress fractures. METHODS: Bilateral, synchronised plantar pressure and lower limb kinematic data were recorded during barefoot running at 3.6 m s-1 (±5%) pre- and post- a 12.8-km training activity (∼150 min). The training activity was completed with an average speed typical of walking (1.4 m.s-1), and 35.5 kg of additional load was carried throughout. Data were collected from 32 male Royal Marines recruits who completed the training activity in week-21 of the 32-week training programme. Plantar pressure variables and ankle dorsiflexion were compared between pre- and post-activity. RESULTS: Post-activity there was reduced loading under the forefoot and increased loading under the rearfoot and midfoot. There was no change in dorsiflexion touchdown angle, but an increase in peak dorsiflexion and range of motion post-activity. SIGNIFICANCE: The increased rearfoot loading, reduced forefoot loading and increased ankle dorsiflexion following a prolonged military load carriage activity suggest a reduced transfer of loading from the rearfoot to the forefoot during stance, which may have implications for the development of stress fractures, particularly of the metatarsals.

Heart rate variability and plasma nephrines in the evaluation of heat acclimatisation status.

PURPOSE: Heat adaptation (HA) is critical to performance and health in a hot environment. Transition from short-term heat acclimatisation (STHA) to long-term heat acclimatisation (LTHA) is characterised by decreased autonomic disturbance and increased protection from thermal injury. A standard heat tolerance test (HTT) is recommended for validating exercise performance status, but any role in distinguishing STHA from LTHA is unreported. The aims of this study were to (1) define performance status by serial HTT during structured natural HA, (2) evaluate surrogate markers of autonomic activation, including heart rate variability (HRV), in relation to HA status. METHODS: Participants (n = 13) were assessed by HTT (60-min block-stepping, 50% VO2peak) during STHA (Day 2, 6 and 9) and LTHA (Day 23). Core temperature (Tc) and heart rate (HR) were measured every 5 min. Sampling for HRV indices (RMSSD, LF:HF) and sympathoadrenal blood measures (cortisol, nephrines) was undertaken before and after (POST) each HTT. RESULTS: Significant (P < 0.05) interactions existed for Tc, logLF:HF, cortisol and nephrines (two-way ANOVA; HTT by Day). Relative to LTHA, POST results differed significantly for Tc (Day 2, 6 and 9), HR (Day 2), logRMSSD (Day 2 and Day 6), logLF:HF (Day 2 and Day 6), cortisol (Day 2) and nephrines (Day 2 and Day 9). POST differences in HRV (Day 6 vs. 23) were + 9.9% (logRMSSD) and - 18.6% (logLF:HF). CONCLUSIONS: Early reductions in HR and cortisol characterised STHA, whereas LTHA showed diminished excitability by Tc, HRV and nephrine measures. Measurement of HRV may have potential to aid real-time assessment of readiness for activity in the heat.

Asymptomatic group A Streptococcal throat carriage in Royal Marines recruits and Young Officers.

AIMS: A prospective observational study was conducted in Royal Marines (RM) recruits to investigate throat carriage of group A Streptococcus (GAS) and incidence of soft tissue infections. METHODS: 1012 RM recruits were followed through a 32-week training programme, with throat swabs being obtained in weeks 1, 6, 15, and 32. Alongside a separate cohort of 46 RM Young Officers (YO) undergoing training were sampled in parallel. RESULTS: Carriage of group A Streptococcus was detected in only 5/1012 (0.49%) recruits at the beginning of training and remained low throughout training. There was no association between GAS carriage and development of soft tissue infection. There was no carriage of GAS in the smaller YO cohort at the start of training, (0/46). At week 6, a surge in GAS carriage was detected in 8/46 (17%) YO, that could be ascribed to a cluster of GAS genotype emm83. CONCLUSIONS: Asymptomatic GAS carriage is very infrequent among young adults in England and this should be borne in mind when considering the relevance of a positive throat swab result in symptomatic patients or outbreaks. Despite low prevalence, there is however potential for GAS to rapidly and transiently disseminate among adults during outbreaks.

Low serum 25-hydroxyvitamin D is associated with increased risk of stress fracture during Royal Marine recruit training.

UNLABELLED: The aim of this study was to investigate vitamin D status and stress fracture risk during Royal Marine military training. Poor vitamin D status was associated with an increased risk of stress fracture. Vitamin D supplementation may help to reduce stress fracture risk in male military recruits with low vitamin D status. INTRODUCTION: Stress fracture is a common overuse injury in military recruits, including Royal Marine (RM) training in the UK. RM training is recognised as one of the most arduous basic training programmes in the world. Associations have been reported between serum 25-hydroxyvitamin D (25(OH)D) and risk of stress fracture, but the threshold of 25(OH)D for this effect remains unclear. We aimed to determine if serum 25(OH)D concentrations were associated with stress fracture risk during RM training. METHODS: We prospectively followed 1082 RM recruits (males aged 16-32 years) through the 32-week RM training programme. Troops started training between September and July. Height, body weight and aerobic fitness were assessed at week 1. Venous blood samples were drawn at weeks 1, 15 and 32. Serum samples were analysed for 25(OH)D and parathyroid hormone (PTH). RESULTS: Seventy-eight recruits (7.2 %) suffered a total of 92 stress fractures. Recruits with a baseline serum 25(OH)D concentration below 50 nmol L(-1) had a higher incidence of stress fracture than recruits with 25(OH)D concentration above this threshold (χ(2) (1) = 3.564, p = 0.042; odds ratio 1.6 (95 % confidence interval (CI) 1.0-2.6)). Baseline serum 25(OH)D varied from 47.0 ± 23.7 nmol L(-1) in February, to 97.3 ± 24.6 nmol L(-1) in July (overall mean 69.2 ± 29.2 nmol L(-1), n = 1016). There were weak inverse correlations between serum 25(OH)D and PTH concentrations at week 15 (r = -0.209, p < 0.001) and week 32 (r = -0.214, p < 0.001), but not at baseline. CONCLUSION: Baseline serum 25(OH)D concentration below 50 nmol L(-1) was associated with an increased risk of stress fracture. Further studies into the effects of vitamin D supplementation on stress fracture risk are certainly warranted.

The gonadotrophic response of Royal Marines during an operational deployment in Afghanistan.

Military training has been associated with changes in the hypothalamic-pituitary-gonadal axis consistent with central hypogonadism. Often such changes have been associated with body mass loss, though sleep deprivation and other psychological stress may also contribute. The effects of deployment in a combat zone on the hypothalamic-pituitary-gonadal axis in military personnel are not known. The objective was to investigate the hypothalamic-pituitary-gonadal axis in male military personnel deployed in Afghanistan. Eighty-nine Royal Marines were investigated pre-deployment, following 3 months in Afghanistan and following 2 weeks mid-tour leave. Testosterone, sex hormone-binding globulin (SHBG), follicle-stimulating hormone (FSH), luteinising hormone (LH), 17-hydroxyprogesterone, androstenedione (AD) and insulin were assayed and body mass recorded. The results showed that body mass (kg) dropped from 83.2 ± 9.2 to 79.2 ± 8.2 kg during the first 3 months of deployment (p < 0.001). Total testosterone did not change, but SHBG increased (30.7 ± 9.7 vs. 42.3 ± 14.1 nmol/L, p < 0.001), resulting in a significant (p < 0.001) fall in calculated free testosterone (435.2 ± 138 vs. 375.1 ± 98 pmol/L). Luteinising hormone and FSH increased by 14.3% (p < 0.001) and 4.9% (p = 0.003) respectively. Free testosterone, SHBG, LH and FSH returned to baseline following 2 weeks of mid-tour leave. Androstenedione (AD) decreased by 14.5% (p = 0.024), and insulin decreased by 26% (p = 0.039), over the course of deployment. In this study of lean Royal Marines, free testosterone decreased during operational deployment to Afghanistan. There was no evidence to suggest major stress-induced central hypogonadism. We postulate that reduced body mass, accompanied by a decrease in insulin and AD synthesis, may have contributed to an elevated SHBG, leading to a decrease in free testosterone.

Changes in vitamin D and matrix metalloproteinase-9 in submariners during a submerged patrol.

OBJECTIVES: To quantify changes in vitamin D and matrix metalloproteinase-9 (MMP9) in submariners over a single long patrol and compare the data to a group of non-deploying servicemen from their base port. METHODS: A prospective time-series analysis was performed. Blood samples were taken from 49 submariners deploying on patrol and 43 shore-side controls from the base port (naval officers from base or non-deploying submariners), following a winter ashore at latitude 56° north. Samples were drawn immediately before the submarine sailed, in January, and again in the final week of patrol 85 days later. Paired pre-patrol and late samples from each individual were assayed together and changes in vitamin D and MMP9 were assessed. RESULTS: Mean pre-patrol vitamin D concentrations were 58 and 49 nmol/L for the controls and submariners, respectively. Mean vitamin D concentrations increased in controls as expected (mean increase 12.6 nmol/L), but not in the submariners (mean decrease 1.6 nmol/L). MMP9 levels were significantly higher in submariners pre-patrol, and increased significantly during the patrol. There was a significant inverse correlation between MMP9 and vitamin D levels (r=-0.41, p=0.01). CONCLUSIONS: This is the first study to quantify vitamin D and MMP levels in submariners. Circulating vitamin D concentrations on board were insufficient to prevent a rise in MMP. This has potential for adverse health effects and requires further study.

Improving the selection of candidates for Royal Marine recruit training by the use of a combination of performance tests.

Candidates who wish to undertake Royal Marine recruit training, a physically strenuous course which now extends 32 weeks, must first of all successfully complete a Personal Qualities Assessment (PQA) and four psychomotor tests (Naval Recruiting Tests or RTs) before attending a three-day selection course at the Commando Training Centre, Lympstone, where their physical capabilities are tested to the full. The effectiveness of these procedures was untested until the Institute of Naval Medicine conducted a retrospective study during 1999-2000 from which the present study is taken. Data from 1232 recruits were examined to explore the relationship between the outcome of Commando training (pass or fail) with these various selection measures. Estimated aerobic power, time to complete the assault course and age were associated with outcome, as were PQA, RTs 1, 3, 4 and total RT score. A regression equation comprising aerobic fitness, assault course time, RT4 and age gave the best overall prediction of outcome (64%). It is suggested that this mathematical approach provides a scientifically valid and objective assessment tool for future selection strategies.

Survival of the fittest? The scientific basis for the Royal Navy pre-joining fitness test.

The Royal Navy introduced a pre-joining fitness test to the selection procedures for RN Ratings from Summer 2003. The scientific basis for the test came from the present study to investigate if anthropometric and physical fitness measures predicted training failure. Fitness and anthropometric data from 1641 trainees were collected, together with their training outcome (i.e. pass or fail), during the period from September 2001 to March 2002. In addition, a retrospective interrogation of medical records identified those who reported any lower limb injuries. The overall rate of training attrition was 22%. Success in training was associated with: gender; age; physical fitness; and, in the case of females, Body Mass Index (BMI). The reported incidence of lower limb injury (LLI) was associated with: gender; physical fitness; and, for female trainees, BMI. The reported incidence of LLI was approximately 50% in the 'least-fit' female group compared to 10% in the 'most-fit' male group. 16% of females and 2% of males were considered 'unfit' (i.e. did not attain the prescribed run standards of 13 min 15 s and 11 min 13 s respectively). 3% of trainees were considered 'obese' (a BMI > 30 kg.m-2) whereas more than 25% were overweight (BMI > 25 kg.m-2). As a result of this work, selection candidates must now demonstrate a minimum standard of aerobic fitness prior to arrival at HMS Raleigh. The future impact of this selection measure on the reported incidence of lower limb injury and financial costs of training requires further investigation.

Generic task-related occupational requirements for Royal Naval personnel.

Physical tests and selection criteria have historically been used by many military organizations. However, the standards associated with them have come under increasing scrutiny in recent years. This paper describes a series of experiments that were conducted to establish task-related occupational tests and standards (TBTs) for Royal Naval (RN) personnel. A total of 172 (106 male and 66 female) RN personnel volunteered for these experiments, which were designed to: identify the anthropometric requirements for operating various safety hatches and doors on board a RN Frigate (TBT1); quantify the metabolic demands of shipboard firefighting tasks and establish an aerobic fitness standard (TBT2); and identify a battery of tests to predict performance of shipboard casualty-carrying tasks (TBT3). Whilst all subjects completed the criterion tasks during TBT1, performance of the bulkhead door (BD) escape task was related to height (r = 0.50- 0.62, P < 0.05) and vertical reach (r = 0.42-0.54, P < 0.05), with shorter subjects struggling to perform the task. During TBT2, the mean metabolic demand of representative firefighting tasks was 38 ml/min/kg, which must be sustained for 20-30 min. Finally, a battery of tests incorporating measures of lean body mass, fat mass, standing broad jump, 20 m sprint, press-ups, sit-ups and grip strength produced a high correlation (r = 0.89, P < 0.01) with casualty-carrying task performance. From the results of these experiments, it is recommended that RN personnel perform the BD simulation task at the recruitment stage (TBT1), to prove that they possess the anthropometric characteristics commensurate with survival at sea. Secondly, personnel should be frequently screened to ascertain whether they have the maximal aerobic power (41 ml/min/kg) commensurate with shipboard firefighting for 20-30 min (TBT2). Finally, they should perform the battery of proposed tests and score at least 34 points, in order to establish whether they have the anaerobic and strength capacity commensurate with shipboard casualty-carrying tasks (TBT3).

Influence of glucose ingestion by humans during recovery from exercise on substrate utilisation during subsequent exercise in a warm environment.

Carbohydrate (CHO) ingestion during short-term recovery from prolonged running has been shown to increase the capacity for subsequent exercise in a warm environment. The aim of this study was to examine the effects of the amount of glucose given during recovery on substrate storage and utilisation during recovery and subsequent exercise in a warm environment. A group of 11 healthy male volunteers took part in two experiments in a controlled warm environment (35 degrees C, 40% relative humidity), 1 week apart. On each occasion the subjects completed two treadmill runs (T1 and T2) at a speed equivalent to 60% of maximal oxygen uptake, for 90 min, until they were fatigued, or until aural temperature (T(aur)) reached 39 degrees C. The two runs were separated by a 4 h recovery period (REC), during which subjects consumed 55 g of naturally enriched [U-(13)C]-glucose in the form of a 7.5% carbohydrate-electrolyte solution (CES, mass of solution 667 g) immediately after T1. The subjects then consumed either: the same quantity of CES, or an equivalent volume of an electrolyte placebo, at 60, 120 and 180 min during REC, providing a total of 220 g (C220) or 55 g (C55) of [U-(13)C]-glucose, respectively. Expired gases were collected at 15 min intervals during exercise and 60 min intervals during REC, for determination of total CHO and fat oxidation by indirect respiratory calorimetry, and orally ingested [U-(13)C]-glucose oxidation, estimated from the (13)C:(12)C ratio of expired CO(2). Substrate metabolism did not differ between conditions during T1. Despite the fact that total CHO (P < 0.05) and ingested glucose oxidation (P < 0.01) were greater during REC of the C220 condition, glycogen synthesis was estimated to be approximately fivefold greater (P < 0.01) than in the C55 condition. During T2 the rate of total CHO oxidation was higher (P < 0.01) and total fat oxidation lower (P < 0.01) at all times during the C220 compared to the C55 condition. The greater CHO oxidation during C220 appeared to be met from ingested sources, as the rate of [U-(13)C]-glucose oxidation was greater (P < 0.01) at all times during T2, compared to C55. Whilst more of the ingested substrate remained unoxidised on completion of T2 during C220, exercise duration was similar in the two experimental conditions, and was limited by thermoregulatory incapacity (T(aur) > 39 degrees C) rather than substrate availability per se.

Assessment of physical fitness for occupations encompassing load-carriage tasks.

There is increasing anecdotal evidence that simple occupational tests of aerobic fitness impose a systematic bias against heavier personnel when predicting fitness for load-carrying tasks. This study tested the hypothesis that simple field tests of aerobic fitness are not good predictors of load-carrying performance and that personnel with greater body mass are more able to perform occupationally relevant load-carrying tasks. Twelve healthy male volunteers ran on a level treadmill at 9.5 km/h for 4 min, with (T18) and without (T0) an external backpack load of 18 kg. During each exercise period, steady-state oxygen uptake (VO(2)) was assessed. On a subsequent occasion (at least 7 days later), 11 of the subjects ran to exhaustion at 9.5 km/h whilst carrying the 18 kg external load (ETT18). There was a strong inverse linear relationship between relative VO(2) and body mass (r = -0.87, P < 0.01) and between VO(2) and lean body mass (r = -0.74, P < 0.01) during the T18 trials. Furthermore, there was a moderately strong relationship between exercise time (ETT18) and body mass (r = 0.69, P < 0.05) and between exercise time and lean body mass (r = 0.71, P < 0.05). There was no relationship between exercise tolerance time and VO(2) (r = 0.12). The results show that fitness tests that determine aerobic power in units relative to body mass (e.g. timed distance run) incur a systematic bias against heavier personnel. Such tests are therefore inappropriate when predicting the ability of personnel to work in occupations that encompass load-carrying tasks.

Short-term recovery from prolonged constant pace running in a warm environment: the effectiveness of a carbohydrate-electrolyte solution.

Recovery from prolonged exercise involves both rehydration and replenishment of endogenous carbohydrate stores. This study examined the influence of drinking a carbohydrate-electrolyte solution on short-term recovery and subsequent exercise capacity in a warm environment. Thirteen healthy male volunteers completed two trials, at least 7 days apart. On each occasion subjects performed an initial treadmill run at 60% of maximal oxygen uptake (VO2max), for 90 min or until volitional fatigue (T1), in a warm environment (35 degrees C, 40% relative humidity, RH). Volitional ingestion of water was permitted during each of the exercise trials. During a subsequent 4-h recovery period (REC) subjects consumed either a 6.9% carbohydrate-electrolyte solution (CES) or a sweetened placebo (P), in a volume equivalent to 140% of body mass loss. Following REC, subjects ran to exhaustion at the same % VO2max in order to assess their endurance capacity (T2). Mean (SEM) run times during T1 did not differ between the CES [74.8 (4.6) min] and P [72.5 (5.2) min] trials. Body mass was reduced (P < 0.01) by 1.9 (0.2)% (CES) and 1.7 (0.2)% (P), and plasma volume (P < 0.01) by 6.0 (0.9)% (CES) and 5.4 (1.0)% (P) during the T1 trials. During REC 2006 (176) ml and 1830 (165) ml of fluid was ingested, providing 138 (12) g and 0 g of carbohydrate in the CES and P trials, respectively. Prior to T2, plasma volume and net fluid balance were similarly restored [CES +58 (26) g; P -4 (68) g] in both trials. During T2 the exercise duration was longer (P < 0.01) in the CES compared to the P trial [CES 60.9 (5.5) min; P 44.9 (3.0) min]. Thus, provided that an adequate hydration status is maintained, inclusion of carbohydrate within an oral rehydration solution will delay the onset of fatigue during a subsequent bout of prolonged submaximal running in a warm environment.

The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration.

The effect of manipulating sodium intake upon sweat sodium secretion was investigated during heat acclimation. Twenty-five male subjects were confined to an environmental chamber at a temperature of 25 degrees C for 3 days, and then acclimated to heat by a further 5 days at 40 degrees C. The subjects' daily sodium intake was controlled throughout as follows: high (HNa), 348.4 (0.8) mmol x day(-1), n=7; moderate (MNa), 174.1 (0.6) mmol x day(-1), n=9; or low (LNa), 66.3 mmol x day(-1), n=9. Sodium losses were estimated from urinary, faecal and sweat collections using a whole-body washdown method. Plasma aldosterone concentration was also measured from venous blood sampled each morning. Measurements of body temperature and heart rate during the heat exposure phase indicated a degree of heat acclimation. During this heat phase there was a reduction (P < 0.01) in sweat sodium secretion for all three conditions which was greatest for the LNa condition, although this finding was not significant (P < 0.1). In the LNa condition, plasma aldosterone concentration increased (P < 0.05) prior to heat exposure, and the secretion of aldosterone was potentiated (P < 0.01) during the heat exposure in comparison with the MNa condition. In contrast, the HNa diet produced a fall (P < 0.05) in plasma aldosterone concentration prior to heat exposure and an attenuation of aldosterone secretion thereafter. These findings are inconsistent with the hypothesis that retention of sweat sodium is dependent upon a net body sodium deficit, but demonstrate that aldosterone secretion is potentiated under such conditions.

Prevention of heat strain by immersing the hands and forearms in water.

The effectiveness of hand immersion in water at 10 degrees C, 20 degrees C and 30 degrees C as a technique for reducing heat strain in Royal Navy (RN) personnel has been investigated at the Institute of Naval Medicine (INM). Four subjects exercised at a moderate work rate, whilst wearing fire fighting clothing in an environmental chamber at 40 degrees C. The subjects reached heat strain safety limits within 45 minutes of commencing work at which point they rested in the heat for 30 minutes whilst they underwent one of four experimental conditions: without intervention (control); or with their hands immersed in water at 10 degrees C, 20 degrees C or 30 degrees C. The experiment was repeated on a further three days so that the subjects undertook each experimental condition in a balanced randomised order. During the control condition without hand immersion the subjects were unable to cool. Immersion of the hands in water (at 10 degrees C, 20 degrees C or 30 degrees C) significantly (P < 0.05) lowered body core (auditory canal) temperature within ten minutes. Assessing the effectiveness of this technique by the initial rates of core temperature reduction, revealed that immersion of the hands was more effective the colder the water. Following 20 minutes of hand immersion mean core temperature had dropped from 38.5C to: 36.9(standard deviation 0.19) degrees C, 37.3(0.18) degrees C, and 37.8(0.10) degrees C, in 10 degrees C, 20 degrees C and 30 degrees C water respectively. Cooling powers estimated from changes in mean body temperature were 334, 307 and 113 watts using 10 degrees C, 20 degrees C and 30 degrees C water respectively. These results indicate that hand immersion in water at a temperature of between 10 degrees C and 30 degrees C is an efficient means of cooling heat stressed personnel who have been exercising. This simple and effective technique may be applied to many industrial and military tasks to reduce heat strain, lower the risk of heat injury, and increase safe total work times in the heat. For the RN, hand immersion could be used in fire fighting, damage control and NBC operations where personnel alternately work and rest.

Changes in selected parameters of health and physical fitness following a sixteen-week deployment at sea.

The effects of 16 weeks at sea upon selected parameters of health and physical fitness were investigated in 30 male volunteers (from a total crew of 48 men) prior to, and immediately following deployment. The 30 subjects were assigned to either an exercise group, 'Ex' (n = 12), or a non-exercising group, 'Nilex' (n = 18), according to their reported participation in vigorous training or sports. Body mass index (BMI), calculated from height and weight, revealed that prior to deployment 13 of the 30 subjects (two in the Ex group) had a BMI over 25 kg.m-2 (i.e. overweight), and a further three subjects (all 'non-exercisers') had values of 30 kg.m-2 or more (obese). In addition, the diastolic blood pressure of two subjects was in excess of 95 mmHg and five subjects had resting heart rates above 89 beats per minute. Retrospective comparisons between the Ex and Nilex groups revealed a significantly lower percentage body fat (P < 0.01) and a faster rate of cardiac recovery (P < 0.05) following a standardised bout of exercise in the Ex group, albeit that these individuals were significantly younger (mean age of 24 years) than those in the Nilex group (32 years). Following deployment, in the Nilex group, comparison of pre- and post values showed that resting heart rate was elevated (P < 0.01) on return from sea. Similarly, in the Nilex group heart rate while performing the standardised exercise bout was also elevated (P < 0.05) on the second test occasion.(ABSTRACT TRUNCATED AT 250 WORDS)

Hand immersion as a method of cooling and rewarming: a short review.

Many cooling and warming procedures have been proposed for the treatment of hyperthermic or hypothermic individuals. One of the most recent of these is the use of hand immersion as a simple method to gain or lose heat. In the present paper the principles underlying this approach, and the evidence for and against hand rewarming/cooling, are briefly reviewed. It is concluded that hand immersion is likely to be more effective for cooling than rewarming individuals.

The effect of hand immersion on body temperature when wearing impermeable clothing.

The effects of hand immersion on body temperature have been investigated in men wearing impermeable NBC clothing. Six men worked continuously at a rate of approximately 490 J. sec-1 in an environmental temperature of 30 degrees C. Each subject was permitted to rest for a period of 20 minutes when their aural temperature reached 37.5 degrees C, and again on reaching 38 degrees C, and for a third time on reaching 38.5 degrees C (three rest periods in total). Each subject completed three experimental conditions whereby, during the rest periods they either: a. Did not immerse their hands (control). b. Immersed both hands in a water bath set at 25 degrees C. c. Immersed both hands in water at 10 degrees C. Physiological measures of core temperature, skin temperature and heart rate were recorded at intervals throughout the experiment. Measures of mean aural temperature and mean skin temperature were significantly (P less than 0.05) reduced if hands were immersed during these rest periods, compared to non immersion. As a result, the total work time of subjects was extended when in the immersed conditions by some 10-20 minutes within the confines of the protocol. It is concluded that this technique of simple hand immersion may be effective in reducing heat stress where normal routes to heat loss are compromised.