It is important to understand how people adapt their gait when walking in real-world conditions with variable surface characteristics. This study quantified lower-extremity joint kinematics, estimated whole body center of mass height (COMVT), and minimum toe clearance (MTC) while fifteen healthy, young subjects walked on level ground (LG) and a destabilizing loose rock surface (RS) at four controlled speeds. There were no significant differences in average step parameters (length, time, or width) between the walking surfaces. However, the variability of these parameters increased twofold on the RS compared to LG. When walking on the RS, subjects contacted the surface with a flatter foot and increased knee and hip flexion, which enabled them to lower COMVT. Subjects exhibited increased hip and knee flexion and ankle dorsiflexion during swing on the RS. These changes contributed to a 3.8 times greater MTC on the RS compared to LG. Peak hip and knee flexion during early stance and swing increased with walking speed, contributing to decreased COMVT and increased MTC. Overall, subjects systematically adapted their movement kinematics to overcome the challenge imposed by the destabilizing loose rock surface.

Uneven walking surfaces pose challenges to balance, especially in individuals with lower extremity amputation. The purpose of this study was to determine if lateral stability of persons with unilateral transtibial amputation (TTA) is compromised when walking on a loose rock surface. Thirteen TTA and 15 healthy controls walked over level ground and over a loose rock surface at four controlled speeds. Dependent measures, including medial-lateral center of mass (COM) motion, step width variability, lateral arm swing velocity, and mean and variability of the minimum margins of stability (MOSmin), were compared between subject groups and across conditions. TTA had greater average MOSmin than Control subjects (p = 0.018). TTA exhibited decreased MOSmin on their prosthetic limbs compared to their intact limbs (p = 0.036), while Control subjects did not exhibit side to side differences. Both groups increased MOSmin with increasing walking speed (p ≤ 0.001). There was no difference in the average MOSmin between walking surfaces (p = 0.724). However, the variability of MOSmin was greater on the rocks compared to level ground. Both subject groups increased step width, step width variability, COM range of motion and peak COM velocity when walking on the rock surface. TTA exhibited greater variability of both step width and MOSmin, which suggests that they made larger step-to-step, corrective responses, more often, to achieve the same average result.

Recruits arriving for basic combat training (BCT) between October 1999 and May 2004 were administered an entry-level physical fitness test at the reception station. If they failed the test, then they entered the Fitness Assessment Program (FAP), where they physically trained until they passed the test and subsequently entered BCT. The effectiveness of the FAP was evaluated by examining fitness, injury, and training outcomes. Recruits who failed the test, trained in the FAP, and entered BCT after passing the test were designated the preconditioning (PC) group (64 men and 94 women). Recruits who failed the test but were allowed to enter BCT without going into the FAP were called the no preconditioning (NPC) group (32 men and 73 women). Recruits who passed the test and directly entered BCT were designated the no need of preconditioning (NNPC) group (1,078 men and 731 women). Army Physical Fitness Test (APFT) scores and training outcomes were obtained from a company-level database, and injured recruits were identified from cases documented in medical records. The proportions of NPC, PC, and NNPC recruits who completed the 9-week BCT cycle were 59%, 83%, and 87% for men (p < 0.01) and 52%, 69%, and 78% for women (p < 0.01), respectively. Because of attrition, only 63% of the NPC group took the week 7 APFT, compared with 84% and 86% of the PC and NNPC groups, respectively. The proportions of NPC, PC, and NNPC recruits who passed the final APFT after all retakes were 88%, 92%, and 98% for men (p < 0.01) and 89%, 92%, and 97% for women (p < 0.01), respectively. Compared with NNPC men, injury risk was 1.5 (95% confidence interval, 1.0-2.2) and 1.7 (95% confidence interval, 1.0-3.1) times higher for PC and NPC men, respectively. Compared with NNPC women, injury risk was 1.2 (95% confidence interval, 0.9-1.6) and 1.5 (95% confidence interval, 1.1-2.1) times higher for PC and NPC women, respectively. This program evaluation showed that low-fit recruits who preconditioned before BCT had reduced attrition and tended to have lower injury risk, compared with recruits of similar low fitness who did not precondition.

Individuals with transtibial amputation (TTA) have a high incidence of falls during walking. Environmental factors, such as uneven ground, often play a contributing role in these falls. The purpose of this study was to quantify the adaptations TTA made when walking on a destabilizing loose rock surface. In this study, 13 young TTA walked over a rock surface and level ground level ground at four controlled speeds. Subjects successfully traversed the rock surface by adopting a conservative gait characterized by shorter and wider steps. They also took shorter steps with their prosthetic limbs and exhibited greater variability in foot placement when stepping onto their intact limb. Between-limb differences in step length and width variability increased at faster walking speeds. TTA increased hip and knee flexion during initial stance, which contributed lowering the whole-body center of mass. TTA also increased hip and knee flexion during swing, enabling them to significantly increase their toe clearance on the rock surface compared to level ground. Toe clearance on the prosthetic side was aided by increased ipsilateral hip flexion. The results suggest that TTA were able to adapt their gait to overcome the challenge imposed by the rock surface. These adaptations were asymmetric and initiated proximally.

A control group (CG, n = 1,138) that implemented a traditional Basic Combat Training (BCT) physical training (PT) program was compared to an evaluation group (EG, n = 829) that implemented a PT program newly designed for BCT. The Army Physical Fitness Test (APFT) was taken at various points in the PT program, and injuries were obtained from a medical surveillance system. After 9 weeks of training, the proportion failing the APFT was lower in the EG than in the CG (1.7 vs. 3.3%, p = 0.03). After adjustment for initial fitness levels, age, and body mass index, the relative risk of an injury in the CG was 1.6 (95% confidence interval [CI] =1.2-2.0) and 1.5 (95% CI = 1.2-1.8) times higher than in the EG for men and women, respectively. The newly designed PT program resulted in higher fitness test pass rates and lower injury rates compared to a traditional BCT physical training program.

Low physical fitness levels are associated with increased musculoskeletal injury risk and attrition among military recruits. The authors review physical fitness trends, injury risk factors, and Department of the Army initiatives to address recruit fitness, injuries, and attrition. Initiatives include the Fitness Assessment Program, which reduced injury risk and attrition among low-fit trainees, and the Assessment of Recruit Motivation and Strength, which enabled the Army to enlist individuals exceeding body composition accession standards without increasing attrition. Physical Readiness Training (PRT) is the Army's primary initiative to address training-related injuries and attrition. PRT's inherent injury control and exercise progression components are designed to address low fitness levels across entry-level training. PRT has been shown to decrease injury rates, but low-fit recruits remain at increased risk regardless of program design. The authors recommend resuming pre-enlistment fitness screening and fitness programming before low-fit recruits begin entry-level training. The decision whether to screen for fitness before beginning entry-level training could be based upon the existing recruiting environment in terms of applicant supply and the demand for recruits. However, the Army should anticipate increased injury and attrition rates when discontinuing screening and/or fitness programming for low-fit recruits.

We hypothesized that the use of evidence based injury prevention strategies would lead to a reduction in the incidence of femoral neck stress injuries (FNSIs) and other serious overuse injuries in U.S. Army Basic Combat Training (BCT). An injury prevention strategy began in late 2008 that included: (1) leadership education, (2) leadership enforcement of proven methods, and (3) injury surveillance and reporting. Data on FNSI and removal from training for injury were analyzed based on the fiscal year 2006 through 2010 (n = 210,002). For men, FNSI were reduced from 13 to 20 cases/10,000 recruits per year (2006-2008) to 8 cases/10,000 recruits in 2010 (p < 0.01); for women, FNSI were reduced from 35 to 41 cases/10,000 recruits per year (2006-2008) to 18 cases/10,000 recruits per year in 2010 (p < 0.01). For men, removals from training for injury were reduced from 0.8 to 1.1 cases/100 recruits per year (2006-2008) to 0.5 cases/100 recruits in 2010 (p < 0.01); for women removal from training for injury was reduced from 2.3 to 2.4 cases/100 recruits (2006-2008) to 1.0 case/100 recruits per years in 2010 (p < 0.01). The time course of the changes suggests that following specific injury prevention methods was effective in reducing injuries.

During the first few days of Army Basic Combat Training (BCT), recruits take a running test and after completing this test they are ranked from fast to slow. Four roughly equal-sized "ability groups" are established from these rankings and recruits run together in these groups for their physical training during BCT. In the past, there has been no formal guidance regarding how fast or how far these ability groups should run. To fill this void, this study provides guidance for running speeds and distances during BCT. The major considerations included are: (1) minimizing injuries, (2) the initial aerobic fitness level of recruits, (3) historical improvements in run times during BCT, (4) historical running speeds of the slower individuals in each ability group, (5) running speeds that must be achieved to "pass" the 2-mile run in BCT, (6) the gender composition of the ability groups, and (7) recommendations from the trainers and field testing. Three databases were analyzed that contained a total of 16,716 men and 11,600 women. Four steps were used in the analyses: (1) establishment of run-time cut points for representative ability groups, (2) determination of initial (starting) run speeds, (3) estimation of changes in run speeds with training, and (4) establishment of run speeds and distances for each week of BCT. Efforts were made to (1) keep the running speeds between 70% and 83% of the estimated maximal oxygen uptake (VO2max) for all ability groups, (2) consider the 2-mile running pace of the slower individuals in each ability group, and (3) keep the total running distance for the two slower ability groups below a total of 25 miles, the apparent threshold for increasing injury incidence. A chart provides speeds and distances for each ability group at each week of BCT. Using these recommended speeds and distances should allow trainees to improve their aerobic fitness, pass the Army Physical Fitness Test, and minimize injuries that result in lost training time and, ultimately, lower fitness levels.