The effects of body-borne loads and cadence manipulation on patellofemoral and tibiofemoral joint kinetics during running Richard W. Willy a,n , John D. Willson a , Kara Clowers a , Michael Baggaley a , Nicholas Murray b a Department of Physical Therapy, East Carolina University, Greenville, NC, USA b Department of Kinesiology, East Carolina University, Greenville, NC, USA article info Article history: Accepted 25 October 2016 Keywords: Knee Biomechanics Musculoskeletal model Military Load carriage abstract Understanding how body-borne mass influences knee loads during running and how to modulate these knee loads may assist efforts to reduce the high rate of knee injuries in military populations. We tested a) the extent a 15-kg body-borne load affects peak and cumulative patellofemoral (PFJ) and tibiofemoral (TFJ) contact forces during running and b) if a 7.5% increase in running cadence modulates these contact forces. Compared with unloaded running, the body-borne load increased peak PFJ contact force ( þ0.2 body weights; p ¼0.001) and PFJ impulse ( þ32 body weights per km; p o0.001). Additionally, greater peak total TFJ contact force ( þ0.5 body weights; p o0.001) and greater peak medial TFJ contact force ( þ0.4 body weights; p ¼0.002) resulted with the added load. Similarly, 85 additional body weights of total TFJ impulse per km (p o0.001) and 65 additional body weights of medial TFJ impulse per km (p o0.001) were noted with the added load. The higher cadence condition reduced peak PFJ force ( À0.5 body weights, p o0.001) and PFJ impulse per km ( À15 body weights per km, p o0.016). Reduced peak total and peak medial TFJ contact forces ( À0.8 body weights, p o0.001; À0.5 body weights, p o0.001, respectively) were also found with higher cadence, while reduced total TFJ and medial TFJ impulse per km ( À18.5 body weights per km, p o0.001; À12.2 body weights per km, p o0.001, respectively) were observed. Thus, running with increased cadence eliminated increased knee loads per step but only partially reduced the greater cumulative knee loads per km that resulted with an added 15-kg body- borne load. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Physical training is a key component of military combat training and deployments, often including distance running with and without Soldier-borne loads (Abt et al., 2014; Anderson et al., 2015; Knapik et al., 2004). The amount and configuration of body-borne loads varies widely during physical training and across different military service branches. For instance, deployed infantry in the United States Army carry mean fighting and approach loads of 25 kg and 46 kg, respectively, (Knapik and Reynolds, 2012). However, body-borne loads that are sub-deployment levels are used as part of a progressive load program in basic combat training to incremen- tally increase load capacity in Cadets (Knapik et al. 2012; Knapik and Reynolds, 2012). Other populations, such as ultra-runners (Costa et al., 2012), routinely bear loads of 5–15 kg during running. Therefore, it is of interest to understand the effects of running with body-borne loads that are sub-deployment levels. Due to large training volumes with and without body-borne loads in the aforementioned populations, the knee is particularly susceptible to injury (Fallon, 1996; Hauret et al., 2010; Jones et al., 1993; Khodaee and Ansari, 2012). Specifically, the patellofemoral joint (PFJ) and tibiofemoral joint (TFJ) are the most common sources of knee pain, representing 49% of all musculoskeletal injuries that ultimately result in disability in the United States Soldier (Lincoln et al., 2002). Among TFJ injuries in active duty military, injuries to the medial compartment are particularly common, occurring nearly twice as often as those in the lateral compartment (Jones et al., 2012), suggesting greater medial com- partmental loads. These findings underscore the importance of understanding medial TFJ compartment loading patterns asso- ciated with physical training, with and without body-borne loads. The knee is also the most common site of injury in ultra-mar- athoners, representing 24.0% of all injuries (Hoffman and Krish- nan, 2014; Lopes et al., 2012). Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jbiomech www.JBiomech.com Journal of Biomechanics http://dx.doi.org/10.1016/j.jbiomech.2016.10.043 0021-9290/& 2016 Elsevier Ltd. All rights reserved. n Correspondence to: Department of Physical Therapy, College of Allied Health Sciences, East Carolina University, Greenville, NC 27834, USA. Fax: 252-744-6240. E-mail address: willyr@ecu.edu (R.W. Willy). Journal of Biomechanics 49 (2016) 4028–4033