Walking Slope and Heavy Backpacks Affect Peak and Impulsive Lumbar Joint Contact Forces.

Heavy load carriage is associated with musculoskeletal overuse injury, particularly in the lumbar spine. Steep walking slopes and heavy backpacks separately require adaptation of torso kinematics, but the combined effect of sloped walking and heavy backpack loads on lumbar spine forces is unclear. Backpacks with hip belts can reduce pressure under the shoulder straps; however, it is unknown if wearing a hip belt reduces lumbar joint contact forces. We used a musculoskeletal modeling and simulation approach to quantify peak and impulsive L1L2 and L4L5 lumbar joint contact forces in the anterior/posterior shear and compressive directions during walking on 0° and ±10° slopes, with no backpack and with 40% body weight backpack load using two different configurations (hip belt assisted and shoulder-borne). Both walking slope and backpack load significantly affected shear and compressive forces. The largest peak shear and compressive forces or 1.57 and 5.23 body weights, respectively, exceed recommended limits and were observed during uphill walking with shoulder-borne loads. However, only impulsive force results revealed differences due to the backpack configuration, and this effect depended on walking slope. During downhill walking only, the hip belt assisted configuration resulted compressive impulses lower than during shoulder borne by 0.25 body weight seconds for both L1L2 and L4L5. These results indicate that walking uphill with heavy loads causes high shear and compressive lumbar forces that may increase overuse injury risk. In addition, our results suggest it is especially important to wear a hip belt when walking downhill.

Concentric and eccentric hip musculotendon work depends on backpack loads and walking slopes.

Hip muscle weakness is associated with low back and leg injuries. In addition, hiking with heavy loads is linked to high incidence of overuse injuries. Walking with heavy loads on slopes alters hip biomechanics compared to unloaded walking, but individual muscle mechanical work in these challenging conditions is unknown. Using movement simulations, we quantified hip muscle concentric and eccentric work during walking on 0° and ±10° slopes with, and without 40% bodyweight added loads, and with and without a hip belt. For gluteus maximus, psoas, iliacus, gluteus medius, and biceps femoris long head, both concentric and eccentric work were greatest during uphill walking. For rectus femoris and semimembranosus, concentric work was greatest during uphill and eccentric work was greatest during downhill walking. Loaded walking had greater concentric and eccentric work from rectus femoris, biceps femoris long head, and gluteus maximus. Psoas concentric work was greatest while carrying loads regardless of hip belt usage, but eccentric work was only greater than unloaded walking when using a hip belt. Loaded and uphill walking had high concentric work from gluteus maximus, and high eccentric work from gluteus medius and biceps femoris long head. Carrying heavy loads uphill may lead to excessive hip muscle fatigue and heightened injury risk. Effects of the greater eccentric work from hip flexors when wearing a hip belt on lumbar spine forces and pelvic stability should be investigated. Military and other occupational groups who carry heavy backpacks with hip belts should maintain eccentric strength of hip flexors and hamstrings.

Advancing a U.S. navy shipboard infrastructure for sleep monitoring with wearable technology.

Development of fatigue management solutions is critical to U.S. Navy populations. This study explored the operational feasibility and acceptability of commercial wearable devices (Oura Ring and ReadiBand) in a warship environment with 845 Sailors across five ship cohorts during at-sea operations ranging from 10 to 31 days. Participants were required to wear both devices and check-in daily with research staff. Both devices functioned as designed in the environment and reliably collected sleep-wake data. Over 10,000 person-days at-sea, overall prevalence of Oura and ReadiBand use was 69% and 71%, respectively. Individual use rates were 71 ± 38% of days underway for Oura and 59 ± 34% for ReadiBand. Analysis of individual factors showed increasing device use and less device interference with age, and more men than women found the devices comfortable. This study provides initial support that commercial wearables can contribute to infrastructures for operational fatigue management in naval environments.

Walking slope and heavy backpack loads affect torso muscle activity and kinematics.

The independent effects of sloped walking or carrying a heavy backpack on posture and torso muscle activations have been reported. While the combined effects of sloped walking and backpack loads are known to be physically demanding, how back and abdominal muscles adapt to walking on slopes with heavy load is unclear. This study quantified three-dimensional pelvis and torso kinematics and muscle activity from longissimus, iliocostalis, rectus abdominis, and external oblique during walking on 0° and ± 10° degree slopes with and without backpack loads using two different backpack configurations (hip-belt assisted and shoulder-borne). Iliocostalis activity was greater during downhill and uphill compared to level walking, but longissimus was only greater during uphill. Rectus abdominis activity was greater during downhill and uphill compared to level, while external oblique activity decreased as slopes progressed from down to up. Longissimus, but not iliocostalis, activity was reduced during both backpack configurations compared to walking with no pack. Hip-belt assisted load carriage required less rectus abdominis activity compared to using shoulder-borne only backpacks; however, external oblique was not influenced by backpack condition. Our results revealed different responses between iliocostalis and longissimus, and between rectus abdominis and external obliques, suggesting different motor control strategies between anatomical planes.