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Muscle activity in the leg is tuned in response to impact force characteristics

PainSci » bibliography » Boyer et al 2004
Tags: running, movement, muscle, neat, exercise, self-treatment, treatment

Six articles on PainSci cite Boyer 2004: 1. Is Running on Pavement Risky?2. The Complete Guide to IT Band Syndrome3. The Complete Guide to Patellofemoral Pain Syndrome4. Complete Guide to Plantar Fasciitis5. Shin Splints Treatment, The Complete Guide6. Are Orthotics Worth It?

PainSci notes on Boyer 2004:

Numerous measures of impact and muscle activity were taken in five different types of shoes, with one notable finding: “muscle activity is tuned to impact force characteristics to control the soft-tissue vibrations.” In other words, we minimize the tissue vibrations caused by impact with a subtle but precise muscular bracing, analogous to the way sound-cancelling headphones work — which is pretty cool. The idea of “muscle tuning” has been explored by Dr. Benno Nigg in a series of several papers with various co-authors over many years (see also Friesenbichler 2011).

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

Based on results from quasi-static experiments, it has been suggested that the lower extremity muscle activity is adjusted in reaction to impact forces with the goal of minimizing soft-tissue vibrations. It is not known whether a similar muscle tuning occurs during dynamic activities. Thus, the purpose of this study was to determine the effect of changes in the input signal on (a) vibrations of lower extremity soft-tissue packages and (b) EMG activity of related muscles during heel-toe running. Subjects performed heel-toe running in five different shoe conditions. Ground reaction forces were measured with a KISTLER force platform, soft-tissue vibrations were measured with tri-axial accelerometers and muscle activity was measured using surface EMG from the quadriceps, hamstrings, tibialis anterior and triceps surae groups from 10 subjects. By changing both the speed of running and the shoe midsole material the impact force characteristics were changed. There was no effect of changes in the input signal on the soft-tissue peak acceleration following impact. A significant correlation (R2=0.819) between the EMG pre-activation intensity and the impact loading rate changes was found for the quadriceps. In addition, the input frequency was shown to approach the vibration frequency of the quadriceps. This evidence supports the proposed paradigm that muscle activity is tuned to impact force characteristics to control the soft-tissue vibrations.

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