E. A. Harman

Soldier Load Carriage: Historical, Physiological, Biomechanical, and Medical Aspects

This study reviews historical and biomedical aspects of soldier load carriage. Before the 18th century, foot soldiers seldom carried more than 15 kg while on the march, but loads have progressively risen since then. This load increase is presumably due to the weight of weapons and equipment that incorporate new technologies to increase protection, firepower, communications, and mobility. Research shows that locating the load center of mass as close as possible to the body center of mass results in the lowest energy cost and tends to keep the body in an upright position similar to unloaded walking. Loads carried on other parts of the body result in higher energy expenditures: each kilogram added to the foot increases energy expenditure 7% to 10%; each kilogram added to the thigh increases energy expenditure 4%. Hip belts on rucksacks should be used whenever possible as they reduce pressure on the shoulders and increase comfort. Low or mid-back load placement might be preferable on uneven terrain but high load placement may be best for even terrain. In some tactical situations, combat load carts can be used, and these can considerably reduce energy expenditure and improve performance. Physical training that includes aerobic exercise, resistance training targeted at specific muscle groups, and regular road marching can considerably improve road marching speed and efficiency. The energy cost of walking with backpack loads increases progressively with increases in weight carried, body mass, walking speed, or grade; type of terrain also influences energy cost. Predictive equations have been developed, but these may not be accurate for prolonged load carriage. Common injuries associated with prolonged load carriage include foot blisters, stress fractures, back strains, metatarsalgia, rucksack palsy, and knee pain. Load carriage can be facilitated by lightening loads, improving load distribution, optimizing load-carriage equipment, and taking preventive action to reduce the incidence of injury.

The effects of arms and countermovement on vertical jumping.

Countermovement and arm-swing characterize most jumping. For determination of their effects and interaction, 18 males jumped for maximal height from a force platform in all four combinations of arm-swing/no-arm-swing and countermovement/no-countermovement. For all jumps, vertical velocity peaked 0.03 s before and dropped 6-7% by takeoff. Peak positive power averaged over 3,000 W, and occurred about 0.07 s before takeoff, shortly after peak vertical ground reaction force (VGRF) and just before peak vertical velocity. Both countermovement and arm-swing significantly (P less than 0.05) improved jump height, but arm-swings effect was greater, enhancing peak total body center of mass (TBCM) rise both pre and posttakeoff. Countermovement only affected the post-takeoff rise. The arm-swing resulted in higher peak VGRF and peak positive power. During countermovement, the use of arms resulted in less unweighting, slower and less extensive TBCM drop, and less negative power. Countermovement increased pretakeoff jump duration by 71-76%, increased average positive power, and yielded large positive and negative impulses. High test-retest reliability was shown for jump descriptive variables. Body weight together with peak posttakeoff TBCM rise effectively predicted peak power (multiple R2 = 0.89, standard error of estimate = 243 W). The results lend insight into which jumping techniques are most appropriate for given sports situations and indicate that a jump test can effectively be used to estimate peak power output.

Lower limb morphology and risk of overuse injury among male infantry trainees.

The effect of anatomic variation on the risk of overuse injuries has not been adequately evaluated. To determine the association of several common anatomic characteristics (genu varum, genu valgum, genu recurvatum, and lower limb length differences) with risk of overuse injury, we made prospective morphologic measurements of young men prior to beginning 12 week of Army infantry training. The training included frequent running, marching, calisthenics, and other vigorous activities. Lower extremity anatomic landmarks were high-lighted, and front- and side-view photographic slides were taken of the 294 study volunteers. The slides were compute digitized, and the following measures calculated: pelvic width to knee width ratio (to assess genu valgum/varum), quadriceps angle (Q-angle), knee angle at full extension, and lower limb length differences. The cumulative incidence of lower limb overuse injury was 30%. Relative risk of (RR) of overuse injury was significantly higher among participants with the most valgus knees (RR = 1.9). Those with Q-angle of more than 15 degrees had significantly increased risk specifically for stress fractures (RR = 5.4). Anatomic characteristics were associated with several other types of injuries, including pain and nonacute muscle strain due to overuse. This pilot study provides evidence that some lower limb morphologic characteristics may place individuals at increased risk of overuse injuries.

Effects of a Belt on Intra-Abdominal Pressure during Weight Lifting

Intra-abdominal pressure (IAP) has been widely hypothesized to reduce potentially injurious compressive forces on spinal discs during lifting. To investigate the effects of a standard lifting belt on IAP and lifting mechanics, IAP and vertical ground reaction force (GRF) were monitored by computer using a catheter transducer and force platform while nine subjects aged 28.2 +/- 6.6 yr dead-lifted a barbell both with and without a lifting belt at 90% of maximum. Both IAP and GRF rose sharply from the time force was first exerted on the bar until shortly after it left the floor, after which GRF usually plateaued while IAP either plateaued or declined. IAP rose significantly (P less than 0.05) earlier with than without the belt. When the belt was worn, IAP rose significantly earlier than did GRF. Both with and without the belt, IAP ended its initial surge significantly earlier than did GRF. Variables significantly greater with than without a belt included peak IAP, area under the IAP vs time curve from start of initial IAP surge to lift-off, peak rate of IAP increase after the end of its initial surge, and average IAP from lift-off to life completion. In contrast, average rate of IAP increase during its initial surge was significantly lower with the belt. Correlations are presented which provide additional information about relationships among the variables. Results suggest that the use of a lifting belt increases IAP, which may reduce disc compressive force and improve lifting safety.

Combined resistance and endurance training improves physical capacity and performance on tactical occupational tasks

The purpose of this study is to evaluate the effectiveness of aerobic endurance (E), strength (R), and combined endurance and strength (CB) training for improving performance of tactical occupational tasks and determine if combined training interferes with performance enhancements of E or R alone. A total of 56 recreationally active women were randomly placed into four groups: R (nxa0=xa018), E (nxa0=xa013), CB (nxa0=xa015), Control (nxa0=xa010). Subjects trained three non-consecutive days per week for 8xa0weeks. Performance was measured pre-, mid-, and post-training for bench press one-repetition maximum (1-RM), squat 1-RM, bench press throw and squat jump peak power, VO2peak, 3.2xa0km load carriage (LC), 3.2xa0km run (run), and repetitive lift and carry (RLC). R and E demonstrated improvements which were generally specific to their training. R improved squat (48.3%) and bench press 1-RM (23.8%), bench press throw (41.9%), RLC (31.3%), and LC (11.5%). E improved run (14.7%), VO2peak (6.2%), squat 1-RM (15.3%), LC (12.9%), and RLC (22.5%). CB improved squat (37.6%) and bench press 1-RM (20.9%), bench press throw (39.6%), VO2peak (7.6%), run (10.4%), LC (13.1%), and RLC (45.5%). Post-training 1-RM squat was greater in R and CB than E, while E completed the 3.2xa0km load carriage task faster than C. In conclusion, 8xa0weeks of combined training improved performance in all tactical occupational tasks measured and did not interfere with improvements in strength, power and endurance measures compared to R or E alone.

A systematic review of the effects of physical training on load carriage performance.

Knapik, JJ, Harman, EA, Steelman, RA, and Graham, BS. A systematic review of the effects of physical training on load carriage performance. J Strength Cond Res 26(2): 585–597, 2012—Soldiers are often required to carry heavy loads during military operations. This article reports on a systematic literature review examining the influence of physical training on load carriage performance. Several literature databases, reference lists, and other sources were explored to find studies that quantitatively examined the effects of physical training on the time taken for individuals to complete a set distance carrying an external load, with the majority of the load contained in a backpack. Effect sizes (Cohens d statistic) were used in meta-analyses to examine the changes in load carriage performance after various modes of physical training. Effect sizes quantified training-related changes in terms of SD units. Ten original research studies met the review criteria. Meta-analysis indicated that large training effects (≥0.8SD units) were apparent when progressive resistance training was combined with aerobic training and when that training was conducted at least 3 times per week, over at least 4 weeks. When progressive load-carriage exercise was part of the training program, much larger training effects were evident (summary effect size [SES] = 1.7SD units). Field-based training that combined a wide variety of training modes and included progressive load-carriage exercise was also very effective in improving load carriage performance (SES = 1.1SD units). Aerobic training alone or resistance training alone had smaller and more variable effects, depending on the study. This review indicates that combinations of specific modes of physical training can substantially improve load carriage performance.

Intra-Abdominal and Intra-Thoracic Pressures during Lifting and Jumping,

In order to investigate intra-thoracic pressure (ITP) and intra-abdominal pressure (IAP) during lifting and jumping, 11 males were monitored as they performed the dead lift (DL), slide row (SR), leg press (LP), bench press (BP), and box lift (BL) at 50, 75 and 100% of each subjects four-repetition maxima, the vertical jump (VJ), drop jump (DJ) from 0.5 and 1.0 m heights, and Valsalva maneuver (VM). Measurements were made of peak pressure, time from pressure rise to switch-marked initiation of body movement, and time from the movement to peak pressure. The highest ITP and IAP occurred during VM (22.2 +/- 6.0 and 26.6 +/- 6.7 kPa, respectively) with one individual reaching 36.9 kPa (277 mm Hg) IAP. In ascending order of peak ITP during the highest resistance sets, the activities were SR, BP, VJ, DJ, DL, BL, LP, and VM, while the order for IAP was BP, VJ, DJ, BL, DL, LP, SR, and VM. Pressures significantly (P less than 0.05) increased with amount of weight lifted, rising before and peaking after the weight moved. IAP generally rose earlier and was of greater magnitude than ITP. For the jumps, pressure rose and diminished before the feet lost contact with the ground. Drop-jump height did not affect pressure. Correlation of pressure with weight lifted was fair to good for most activities.

Early Phase Differential Effects of Slow and Fast Barbell Squat Training

To examine the importance of resistance training movement speed, two groups of women (24 4 years, 162 5 cm, 59 7 kg) squatted repeatedly at 1) 2 seconds up, 2 seconds down (slow, N 11); or 2) 1 second up, 1 second down (fast, N 10), doing three warm-up sets and three eight-repetition maximum sets, three times per week for 7 weeks. Tests included force platform and video analysis of the vertical jump, long jump, and maximum squat, and isometric and isokinetic knee extensor testing at speeds from 25 to 125 deg/sec. The groups improved similarly in many variables with training but also showed some differences. In the long jump, the fast group was superior in numerous variables including knee peak velocity and total-body vertical and absolute power. In the vertical jump, fast training affected the ankle and hip more (e.g., average power), and slow training mostly affected the knee (average torque). In isokinetic testing, the fast group improved strength most at the faster velocities, while the slow group strength changes were consistent across the velocities tested. Although both slow and fast training improved performance, faster training showed some advantages in quantity and magnitude of training effects.

Maximal aerobic capacity for repetitive lifting: comparison with three standard exercise testing modes

SummaryA multi-stage, repetitive lifting maximal oxygen uptake (n