Effects Of Load Carriage and Step Length Manipulation on Knee Loads During Walking

Abstract

PURPOSE: Effects of load carriage on medial tibiofemoral joint (mTFJ) and patellofemoral joint (PFJ) contact forces were evaluated using preferred, 7.5% shorter and 7.5% longer step lengths. METHODS: Sixteen male Army ROTC Cadets (20.1 ±2.5 years, 77.4 ±13.4 kg) completed walking treadmill trials (1.3 m/s) with and without 20-kg load carriage. Trials were then collected with altered step lengths (±7.5%) with load carriage. Joint contact forces normalized to body weight (BW) per step and per 1-km were estimated for the mTFJ and PFJ via musculoskeletal modeling. RESULTS: At preferred step length, the load carriage increased peak mTFJ contact force per step by 19.3% (p<0.001, d=1.33) and mTFJ impulse per 1-km by 22% or 89 additional BW*s per km (p<0.001, d=1.49). Relative to body mass, the load carriage increased peak PFJ contact force per step by 14.2% (p<0.001, d=0.66) and PFJ impulse per km by +18.7% or 19 additional BW*s per km (p<0.001, d=0.69). There was a 1:2 relationship between the load carriage and absolute peak mTFJ contact force increase versus a more modest 1:1 relationship between load carriage and absolute peak PFJ contact force increase. Compared with preferred step length with load carriage, a short step with load carriage did not alter mTFJ or PFJ contact forces (all p>0.05). In contrast, a long step magnified the effect of load carriage on all metrics of mTFJ and PFJ contact forces. Specifically, a long step with load carriage increased peak mTFJ contact force by 9.0% (p<0.004, d=0.63) and mTFJ impulse per 1-km by 6.6% or 32.8 additional BW*s per km (p=0.001, d=0.48). A long step increased peak PFJ contact force by 26.6% (p=0.004, d=0.68) and PFJ impulse per 1-km by 22.7% or 27.1 additional BW*s impulse per km (p=0.001, d=0.48) compared with preferred step length with load carriage. A long step with load carriage resulted in 1:3.2 and 1:2.4 relationship between added load weight and absolute increases in peak mTFJ and PFJ contact forces, respectively. CONCLUSIONS: The added load carriage was preferentially borne by the mTFJ with a smaller increase in PFJ contact forces. A short step was not an effective strategy to reduce mTFJ and PFJ loads. A longer than preferred step length, often observed in shorter individuals during formation marching, increased both mTFJ and PFJ contact forces with greatest increases noted in the PFJ.