Cardiorespiratory responses of load carriage in female and male soldiers

PURPOSE

To investigate the effect of sex and load carriage on cardiorespiratory responses to high intensity exercise in male and female soldiers.

METHODS

Soldiers (9 women, 9 men) performed a graded treadmill test until exhaustion with no load (NL) and combat-gear with body armor (CG). Cohen's d effect sizes, paired t-tests and ANOVA were used to study differences between conditions. A mixed linear regression model analyzed the relationship between heart rate (HR) and oxygen uptake (V̇O₂) with load and between sexes.

RESULTS

Wearing CG resulted in, for both sexes, a decreased time to exhaustion (-11 min), lower V̇O_2peak (L/min) ES = 0.56; VO_2peak (mL//kg/min) ES = 2.44, both p < 0.001, a net decrease in minute ventilation (ES = 3.53) and no change in HR_max. No sex-difference were present except for absolute V̇O_2peak. The VO₂ and HR relationship showed a cardiorespiratory reduction wearing CG vs. NL. Added load was equal between sexes, although female soldiers' CG relative to body mass was higher (25%) than male soldiers' (20%), p < 0.01.

CONCLUSION

Wearing CG reduces soldiers' cardiorespiratory capacity and exercise performance level, although the reduction cannot be explained solely based on the added load of CG, instead CG seems to restrict the capacity to fully ventilate. No sex differences were found in relative cardiorespiratory responses to wearing CG compared to NL.

Inspiratory muscle training at sea level improves the strength of inspiratory muscles during load carriage in cold-hypoxia

Inspiratory muscle training (IMT) and functional IMT (IMT_F: exercise-specific IMT activities) has been unsuccessful in reducing respiratory muscle fatigue following load carriage. IMT_F did not include load carriage specific exercises. Fifteen participants split into two groups (training and control) walked 6 km loaded (18.2 kg) at speeds representing ∼50%V̇O_2max in cold-hypoxia. The walk was completed at baseline; post 4 weeks IMT and 4 weeks IMT_F (five exercises engaging core muscles, three involved load). The training group completed IMT and IMT_F at a higher maximal inspiratory pressure (P_imax) than controls. Improvements in P_imax were greater in the training group post-IMT (20.4%, p  = .025) and post-IMT_F (29.1%, p  = .050) compared to controls. Respiratory muscle fatigue was unchanged (p  = .643). No other physiological or subjective measures were improved by IMT or IMT_F. Both IMT and IMT_F increased the strength of respiratory muscles pre-and-post a 6 km loaded walk in cold-hypoxia. Practitioner Summary: To explore the interaction between inspiratory muscle training (IMT), load carriage and environment, this study investigated 4 weeks IMT and 4 weeks functional IMT on respiratory muscle strength and fatigue. Functional IMT improved inspiratory muscle strength pre-and-post a loaded walk in cold-hypoxia but had no more effect than IMT alone. Abbreviations: ANOVA: analysis of variance; BF: breathing frequency; CON: control group; EELV: end-expiratory lung volume; EXP: experimental group; FEV₁: forced expiratory volume in one second; FiO₂: fraction of inspired oxygen; FVC: forced vital capacity; HR: heart rate; IMT: inspiratory muscle training; IMT_F: functional inspiratory muscle training; P_emax: maximal expiratory pressure; P_imax: maximal inspiratory pressure; RMF: respiratory muscle fatigue; RPE: rate of perceived exertion; RWU: respiratory muscle warm-up; SaO₂: arterial oxygen saturation; SpO₂: peripheral oxygen saturation; V̇E: minute ventilation; V̇O₂: rate of oxygen uptake.

The effects of military style ruck marching on lower extremity loading and muscular, physiological and perceived exertion in ROTC cadets

Military ruck marching with load carriage increases ground reaction forces, which are related to bone stress injuries (BSI). This study's purpose was to examine whether a ruck march increases impact loading and to describe muscular, physiological and perceived exertion in Army Reserve Officer Training Corps (ROTC) cadets. Secondary purposes examined relationships among loading changes after the ruck march and baseline characteristics. Fifteen Army ROTC cadets performed a 4-mile march. Lower extremity loading and muscular, physiological and perceived exertion were measured pre- and post-march. Results indicated significant increases in peak impact force and loading rate and decreases in ankle dorsiflexion and plantarflexion strength. Factors that might have been related to changes seen in lower extremity loading did not yield any compelling relationships to explain those changes. In conclusion, the ruck march led to increased peak impact force and loading rate, which have been shown to be related to the risk of BSI. Practitioner summary: This study examined ROTC cadets ankle strength and lower extremity loading before and after a ruck march. We found that lower extremity loading increased after the march, and ankle dorsiflexion (DF) strength decreased, despite the cadets not feeling fatigued. These changes are consistent with risk factors for bone stress injuries. Abbreviations: BSI: bone stress injury; ROTC: Reserve Officer Training Corps; PIF: peak impact force; LR: loading rate; RPE: rate of perceived exertion; APFT: Army physical fitness test; DF: dorsiflexors; PF: plantar-flexors; INV: invertors; EV: evertors; HHD: handheld dynamometer; %HRmax: percentage of maximum heart rate.

Wearing body armour and backpack loads increase the likelihood of expiratory flow limitation and respiratory muscle fatigue during marching

The effect of load carriage on pulmonary function was investigated during a treadmill march of increasing intensity. 24 male infantry soldiers marched on six occasions wearing either: no load, 15 kg, 30 kg, 40 kg or 50 kg. Each loaded configuration included body armour which was worn as battle-fit or loose-fit (40 kg only). FVC and FEV₁ were reduced by 6 to 15% with load. Maximal mouth pressures were reduced post load carriage by up to 11% (inspiratory) and 17% (expiratory). Increased ventilatory demands associated with carrying increased mass were met by increases in breathing frequency (from 3 to 26 breaths·min^-1) with minimal changes to tidal volume. 72% of participants experienced expiratory flow limitation whilst wearing the heaviest load. Loosening the armour had minimal effects on pulmonary function. It was concluded that as mass and exercise intensity are increased, the degree of expiratory flow limitation also increases. Practitioner Summary: This study investigated the effect of soldier load carriage on pulmonary function, to inform the trade-off between protection and burden. Load carriage caused an inefficient breathing pattern, respiratory muscle fatigue and expiratory flow limitation during marching. These effects were exacerbated by increases in mass carried and march intensity.

Influence of Body Mass on Fitness Performance in Naval Special Warfare Operators

Wood, DE and Swain, DP. Influence of body mass on fitness performance in Naval Special Warfare operators. J Strength Cond Res XX(X): 000-000, 2019-U.S. Naval Special Operations Forces have performed some of the U.S. Military's most rigorous missions. The Human Performance Program (HPP) developed a physical performance testing battery to assess and monitor physical fitness. Testing bias relative to body mass has been noted in the past literature, including military physical fitness tests. This retrospective study looked to determine whether there is body mass bias in the HPP fitness assessment and whether an optimum body mass for each fitness test could be determined. Data from 333 subjects (age: 28.4 ± 5.0 years; height: 178.4 ± 6.2 cm; mass: 86.0 ± 9.2 kg) were analyzed to compare body mass with performance on the 8 tests: standing long jump, Pro-Agility test, weighted pull-up, body weight bench press, 1 repetition maximum (1RM) deadlift, 274-m shuttle run, 4.83-km run, and 800-m swim. Linear regression analysis was used to analyze the relationship of body mass to performance; a second-degree polynomial was used to determine best-fit curves for each of the physical fitness tests; analysis of variance was used to examine differences in performance between body mass groups. Significantly better performance for lighter subjects was found in the Pro-Agility test, weighted pull-up, body weight bench press, 274-m shuttle run, and 4.83-km run. Heavier subjects performed better in the 1RM deadlift. Second-degree polynomial regression revealed optimum body mass for the Pro-Agility test, 274-m shuttle run, and 4.83-km run to be 7-16 kg heavier than the lowest body mass. These findings could help professionals better assess and train operators of varying body size.

Effects of Personal Protective Equipment on the Performance of Federal Highway Policemen in Physical Fitness Tests

Marins, EF, Cabistany, L, Bartel, C, Dawes, J, and Del Vecchio, FB. Effects of personal protective equipment on the performance of Federal Highway Policemen in physical fitness tests. J Strength Cond Res 34(1): 11-19, 2020-Personal protective equipment (PPE), worn by police officers, provides protection and can modify physiological and performance responses during physical efforts. Physiological, perceptual, and physical responses were compared with PPE (WPPE) and without PPE (NPPE) among the Brazilian Federal Highway Policemen (FHP). Nineteen (n = 19) FHP completed 2 experimental trials: NPPE and WPPE (load = 8.3 kg). Tests of aerobic and anaerobic power, muscular strength and endurance, as well as change of direction speed (CODS) were performed under both conditions. Heart rate reductions were shown at the second ventilatory threshold (1.4%) and maximal exercise (1.5%) WPPE. In comparison with NPPE, physical performance in the WPPE condition showed decreases in the following: treadmill time at maximal exercise (21%, p < 0.001); time in the isometric trunk test (28.9%, p < 0.001); vertical jump height (11.6 and 10.5%, p < 0.001); standing long jump distance (7.3%, p < 0.001); bar hang time (14.8%, p < 0.05); and CODS (2.6%, p < 0.05). Results indicate that PPE use reduces physical performance of FHP in cardiorespiratory, strength, power, and CODS tests.

An Occupational-Specific O2max Protocol for Structural Firefighters

OBJECTIVE

The aim of this study was to validate a (Equation is included in full-text article.)O2max protocol designed specifically for the occupational demands of firefighters by incorporating the use of personal protective equipment (PPE).

METHODS

Career firefighters completed a stage-graded exercise test (GXT) with submaximal square-wave verification bout while wearing PPE (pants and boots) to determine (Equation is included in full-text article.)O2max. Using the self-reported Physical Activity-Rating (PA-R) scale and an estimated nonexercise regression equation of (Equation is included in full-text article.)O2max for comparison to measured.

RESULTS

Twenty-eight male, career firefighters performed the GXT and square-wave bout. (Equation is included in full-text article.)O2 values (mean ± SD) from the GXT and the square-wave verification bout were 41.04 ± 6.98 and 39.74 ± 6.42 mL/kg/min, respectively (ICC = 0.98, typical error = 0.96 mL/kg/min, CV = 2.4%).

CONCLUSION

Our data suggest an incremental treadmill protocol that incorporates PPE and square-wave verification as an occupational-specific tool to measure cardiovascular fitness in firefighters.

Respiratory Effects of Thoracic Load Carriage Exercise and Inspiratory Muscle Training as a Strategy to Optimize Respiratory Muscle Performance with Load Carriage

Many occupational and recreational settings require the use of protective and/or load-bearing apparatuses worn over the thoracic cavity, known as thoracic load carriage (LC). Compared to normal, unloaded exercise, thoracic LC exercise places an additional demand on the respiratory and limb locomotor systems by altering ventilatory mechanics as well as circulatory responses to exercise, thus accelerating the development of fatigue in the diaphragm and accessory respiratory muscles compared to unloaded exercise. This may be a consequence of the unique demands of thoracic LC, which places an additional mass load on the thoracic cavity and can restrict chest wall expansion. Therefore it is important to find effective strategies to ameliorate the detrimental effects of thoracic LC. Inspiratory muscle training is an intervention that aims to increase the strength and endurance of the diaphragm and accessory inspiratory muscle and may therefore be a useful strategy to optimize performance with thoracic LC.

Load carriage, human performance, and employment standards

The focus of this review is on the physiological considerations necessary for developing employment standards within occupations that have a heavy reliance on load carriage. Employees within military, fire fighting, law enforcement, and search and rescue occupations regularly work with heavy loads. For example, soldiers often carry loads >50 kg, whilst structural firefighters wear 20–25 kg of protective clothing and equipment, in addition to carrying external loads. It has long been known that heavy loads modify gait, mobility, metabolic rate, and efficiency, while concurrently elevating the risk of muscle fatigue and injury. In addition, load carriage often occurs within environmentally stressful conditions, with protective ensembles adding to the thermal burden of the workplace. Indeed, physiological strain relates not just to the mass and dimensions of carried objects, but to how those loads are positioned on and around the body. Yet heavy loads must be borne by men and women of varying body size, and with the expectation that operational capability will not be impinged. This presents a recruitment conundrum. How do employers identify capable and injury-resistant individuals while simultaneously avoiding discriminatory selection practices? In this communication, the relevant metabolic, cardiopulmonary, and thermoregulatory consequences of loaded work are reviewed, along with concomitant impediments to physical endurance and mobility. Also emphasised is the importance of including occupation-specific clothing, protective equipment, and loads during work-performance testing. Finally, recommendations are presented for how to address these issues when evaluating readiness for duty.