Matthew W. McDonald, Alay Parikh, Dr. Tyler N. Brown
Premature knee osteoarthritis (OA) is an increasing problem for military personnel, which may be attributed to the physical activity they routinely perform with body borneload.
Foot progression, such as toe-out or toe-in gait, may increase during locomotor activities, such as running, with body borne load and elevate military personnel’s risk of knee OA. For instance, increasing toe-out reportedly increases knee adduction, specifically the knee adduction moment (KAM), biomechanics related to knee OA that is prevalent in military personnel.
Yet, it is currently unknown if the body borne load military personnel routinely carry during all operational and training exercises, such as running, increases either foot progression or knee adduction.
To examine the effect of body borne load on foot progression angle and knee adduction biomechanics ,and determine whether it differs between sexes when running with body borne load.
20 male and 16 female (Table 1).
Table 1. Subject demographics (N = 36)
|Gender||N||Height (m)||Weight (kg)||Age (years)|
|Male||10||1.79 ± 0.08||81.69 ± 9.42||21.33 ± 2.77|
|Female||16||1.66 ± 0.03||66.86 ± 8.18||21.92 ± 1.97|
Four body borne loads (20, 25, 30 and 35 kg) (Fig.1).
Participants performed three successful run trials with each load, which they required they run at the correct speed (4m/s ± 5%) and only contact the force platform with their dominant limb.
Synchronous GRF data and 3D marker trajectories collected during each run were low-pass filtered (4th order butterworth, 12 Hz). Then, the filtered marker trajectories were processed to obtain 3D knee joint rotations and foot progression, and kinematic and GRF data submitted to inverse dynamics to calculate 3D knee joint moments using Visual 3D (C-Motion, Rockville, MD).
Foot progression angle (FPA) (Fig. 2), and knee abduction joint angle (KAA) and moment (KAM) were calculated across stance phase (0% -100%).
FPA at initial contact (IC) and peak stance (PS) KAA and KAM were submitted to a linear model with load (20, 25, 30 and 35 kg) and sex (male, female) as fixed effects, and subject identity as random effect. Additionally, FPA was considered a covariate for KAA and KAM. Bonferroni procedure was used for multiple comparisons. Alpha was p <0.05.
Sex (p=0.046), but not load (p=0.261) had significant effect on FPA at IC (Table 2). Specifically, males exhibited 3.5 degrees greater foot progression at IC than females during load running.
Table 2. FPA at initial contact for male and female participants with each body borneload
|Gender||20 kg||35 kg||30 kg||35 kg|
Load and sex had a significant effect on PS KAM (p=0.037; p=0.013), but not PS KAA (p=0.111; p=0.681) (Table 3, Fig. 4). Peak KAM was greater for the 35 kg compared 20 kg load (p=0.029), but similar differences were not observed between any other load(p>0.05).
Males exhibited greater 0.16 Nm/kgm PS KAM than females.
Table 3. PS knee adduction moment for male and female participants with each body borne load
|Gender||20 kg||35 kg||30 kg||35 kg|
FPA at IC was a significant covariate for both PS KAM (p=0.003) and KAA (p<0.001) (Fig. 5). For each 1 degree in IC foot progression, participants exhibited 0.01 Nm/kgm increase in PS KAM and 0.2 degree increase in PS KAA,respectively.
Males may be at greater risk of knee OA, as they exhibited 3.5 degrees greater FPA and 0.16 Nm/kgm greater KAM than females. But, the military may decrease risk of knee OA, particularly for males, by modifying foot progression during training programs.
We would like to thank Battelle and Natick Soldier RD&E Center for providing funding for this work.
- Simic et al. OA and Cartilage, 21, 1272–1280,2013.
- Wang et al. Human Move Sci, 64, 213–220,2019.
For questions or comments about this research, contact Matthew McDonald at email@example.com.