- January 18th, 2019, 3:22 am
#937
Given these observed patterns, the authors hypothesized that “running at a step rate greater than one’s preferred would result in decreased muscle activities during the loading response and
increased activities during late swing phase” of the gait cycle.The study protocol involved having 4Nike Air Max Alpha Trainer Hombre 5 individuals run at their preferred speed (i.e., speed was held constant across step rate variations) on an instrumented treadmill at each of three step rate conditions: 1) preferred step rate, 2) +5% of preferred step rate, and 3) +10% of preferred step rate. A digital metronome was used to specify step rates that each runner needed to match for each condition. While the subjects ran at the three step rates, they were filmed with a three-dimensional camera system, ground reaction forces were measured, and muscle activity was recorded using both wired and wireless surface EMG electrodes (having done a bit of EMG work myself in the past, I’m quite envious of wireless capability – technology has advanced rapidly!). EMG recordings were taken from the following muscles: gluteus medius (butt muscle), gluteus maximus (butt muscle), rectus femoris (central quadriceps muscle on thigh), vastus Nike Air Max 1 Femme lateralis (outer quad muscle on thigh), medial and lateral hamstrings (back of thigh), medial gastrocnemius (calf) and tibialis anterior (front, outer shin).Results showed no differences in muscle activation between the preferred step rate and the +5% condition, despite the fact that previous studies have demonstrated postural and loading changes between these conditions. However, when step rate was increased by 10%, the following patterns were observed:
contrary to their initial hypothesisno changes were observed during the loading response initiated by first contact of the foot with the groundactivity of the rectus femoris and tibialis anteriorAs can be seen, muscle activity changes associated with a 10% increase in step rate all occurred during the swing phase (while the foot is not in contact with the ground), with most occurring during mid- to late swing phase as the leg prepares for impending ground contact. The authors suggest that although muscle activity during loading did not change, pre-activation of muscles prior to initial contact influences limb stiffness at contact. They point out that reduced hamstring pre-activation during swing phase has been linked previously to reduced running economy, and they suggest that increased hamstring pre-activity observed at higher step rates might contribute to reduced ]loading at the knee via the effect of this muscle activity on landing posture. They also suggest that increased activity of the gluteal muscles in late swing phase could contribute to the altered movement and loading of the hip that has been observed with increased step rate, and they indicate that increasing step rate might be a good way to facilitate activation of the glutes for therapeutic purposes (e.g., in patients with anterior knee pain where glute strengthening is a common rehab approach).green overstriderLet’s try to translate these results into a clearer description of what is happening. Imagine an overstriding runner who lands with the foot way out in front of the knee and the foot inclined 45 degrees relative to the ground at contact (like the one in the photo to the left). Generally, this type of stride is associated with a fairly low step rate. Now suppose we have this person increase their cadence by 10%. Previous work has shown that this results in the outcomes discussed above: the foot lands flatter, contact shifts closer to the body, the knee is more flexed at contact, and hip and knee loading are reduced. What’s cool about the Chumanov study is that it shows how these postural changes are accomplished at the level of the muscles. Initial leg swing is sped up by activation of the rectus femoris. At the end of swing, contact is pulled closer to the body by the hamstrings, which slow the forward swing of the lower limb just prior to contact, as well as the glutes, which start to pull the thigh back a bit prior to contact. The calf muscle pre-activates to a greater degree, and the tibialis anterior on the front of the shin reduces its activity, resulting in a flatter foot plant.
increased activities during late swing phase” of the gait cycle.The study protocol involved having 4Nike Air Max Alpha Trainer Hombre 5 individuals run at their preferred speed (i.e., speed was held constant across step rate variations) on an instrumented treadmill at each of three step rate conditions: 1) preferred step rate, 2) +5% of preferred step rate, and 3) +10% of preferred step rate. A digital metronome was used to specify step rates that each runner needed to match for each condition. While the subjects ran at the three step rates, they were filmed with a three-dimensional camera system, ground reaction forces were measured, and muscle activity was recorded using both wired and wireless surface EMG electrodes (having done a bit of EMG work myself in the past, I’m quite envious of wireless capability – technology has advanced rapidly!). EMG recordings were taken from the following muscles: gluteus medius (butt muscle), gluteus maximus (butt muscle), rectus femoris (central quadriceps muscle on thigh), vastus Nike Air Max 1 Femme lateralis (outer quad muscle on thigh), medial and lateral hamstrings (back of thigh), medial gastrocnemius (calf) and tibialis anterior (front, outer shin).Results showed no differences in muscle activation between the preferred step rate and the +5% condition, despite the fact that previous studies have demonstrated postural and loading changes between these conditions. However, when step rate was increased by 10%, the following patterns were observed:
contrary to their initial hypothesisno changes were observed during the loading response initiated by first contact of the foot with the groundactivity of the rectus femoris and tibialis anteriorAs can be seen, muscle activity changes associated with a 10% increase in step rate all occurred during the swing phase (while the foot is not in contact with the ground), with most occurring during mid- to late swing phase as the leg prepares for impending ground contact. The authors suggest that although muscle activity during loading did not change, pre-activation of muscles prior to initial contact influences limb stiffness at contact. They point out that reduced hamstring pre-activation during swing phase has been linked previously to reduced running economy, and they suggest that increased hamstring pre-activity observed at higher step rates might contribute to reduced ]loading at the knee via the effect of this muscle activity on landing posture. They also suggest that increased activity of the gluteal muscles in late swing phase could contribute to the altered movement and loading of the hip that has been observed with increased step rate, and they indicate that increasing step rate might be a good way to facilitate activation of the glutes for therapeutic purposes (e.g., in patients with anterior knee pain where glute strengthening is a common rehab approach).green overstriderLet’s try to translate these results into a clearer description of what is happening. Imagine an overstriding runner who lands with the foot way out in front of the knee and the foot inclined 45 degrees relative to the ground at contact (like the one in the photo to the left). Generally, this type of stride is associated with a fairly low step rate. Now suppose we have this person increase their cadence by 10%. Previous work has shown that this results in the outcomes discussed above: the foot lands flatter, contact shifts closer to the body, the knee is more flexed at contact, and hip and knee loading are reduced. What’s cool about the Chumanov study is that it shows how these postural changes are accomplished at the level of the muscles. Initial leg swing is sped up by activation of the rectus femoris. At the end of swing, contact is pulled closer to the body by the hamstrings, which slow the forward swing of the lower limb just prior to contact, as well as the glutes, which start to pull the thigh back a bit prior to contact. The calf muscle pre-activates to a greater degree, and the tibialis anterior on the front of the shin reduces its activity, resulting in a flatter foot plant.