Posterior view Base of support
Knee flexion during stance Peak knee flexion during stance phase is typically around 45 degrees and occurs at slightly different places during stance phase for different runners (Figure 4). Knee flexion during stance is an important part of impact force absorption. Runners with a peak knee flexion that is considerably less than 45 degrees may have less shock absorption ability (Souza, 2016). Figure 4: Knee Flexion During Stance
Base of support refers to running step width according to the placement of the feet in their ground contact location. Viewed from behind, the feet should not overlap in their ground contact location, but rather there should be a small space between them. A narrow base of support where the feet cross over each other has been associated with tibial stress fractures and iliotibial band syndrome. It has also been linked with overpronation. As such, evaluation of running mechanics should include this variable (Souza, 2016). Heel eversion Foot pronation is a running mechanical variable that receives a lot of attention. For example, many running shoes are made specifically to accommodate either under- or overpronation. Foot pronation is a normal part of running and occurs as part of the loading response. It is only problematic when the magnitude or rate of pronation is high (Souza, 2016). Foot pronation is a triplanar motion that occurs around the subtalar joint axis. As such, it is difficult to measure on a two-dimensional video. One component of pronation that can be measured is heel eversion, which can serve as an indicator of degree of pronation (Figure 5). Figure 5: Heel Eversion
Hip extension at late stance Peak hip extension occurs at late stance phase and has an effect on stride length. The optimal amount of available hip extension range of motion may vary depending on pace and an individual’s running form. Souza has outlined several observed compensations for lack of hip extension in late stance: 1. Increase in extension of the lumbar spine. 2. Bounding, which is a compensatory strategy involving increased float time as a means to increase stride length when inadequate hip extension is present. 3. Increase in overstriding where the runner makes contact with the ground too far in front of their center of gravity. 4. Increase in running cadence as a means of increasing running pace when limited hip extension is present (Souza, 2016). Trunk lean Evaluating the lean of the trunk anteriorly may be useful. Recreational runners show anterior trunk inclinations ranging from 5 to 7.5 degrees while elite runners’ trunk lean is around 3 degrees (van Oeveren et al., 2021). It has been shown that an increase in anterior trunk lean results in a lowering of the knee stress loads while a more upright posture leads to greater knee loads. However, Souza (2016) warns that a direct correlation between trunk lean and running injuries has not been established. On an individual basis, it is a factor that should be noted during evaluation and that should be considered as a potential contributor to that runner’s specific injury. Vertical displacement of the center of mass The center of mass of a runner moves up and down vertically in a range of approximately 6 to 10 cm (van Oeveren et al., 2021). It can be measured or estimated by comparing the runner’s highest point during float phase to their lowest point during stance. An increase in vertical displacement of the center of mass results in increased ground reaction force and braking impulse. For this reason, it should be evaluated as a potential contributing factor to your running client’s injury.
Heel eversion refers to the angle between a line that bisects the posterior calcaneus (visualized via the shoe heel counter) and a line that bisects the tibia. Normal heel eversion occurs at midstance and measures between 8 and 12 degrees. Studies have linked increased heel eversion to tibial stress fractures, patellofemoral pain, and Achilles tendinopathy. Runners with excessive rearfoot eversion are sometimes prescribed orthotics; however, the effectiveness of orthotics is inconclusive (Souza, 2016). Toe-in/Toe-out angle When viewed from behind, the normal amount of toe- out (as viewed at the lateral aspect of the shoe) is 5 to 10 degrees and occurs during stance phase (Figure 6). Excess toe-out or the presence of a toe-in position should be noted and the possible contribution to your client’s running injury assessed.
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