Muscle contributions to propelling the body upward differ between skipping and running

Area of Science:

• Biomechanics
• Exercise Physiology
• Human Movement Analysis

Background:

• Skipping is a lower-impact alternative to running, offering reduced knee forces but higher metabolic demands.
• The greater metabolic cost in skipping is linked to increased vertical center-of-mass (COM) displacement.
• Despite higher COM displacement, skipping involves lower muscle force impulses than running.

Purpose of the Study:

• To compare mechanical power flow between body segments during skipping and running.
• To elucidate the mechanisms behind greater vertical displacement in skipping despite lower vertical impulse.
• To investigate how muscle work contributes to the distinct dynamics of skipping versus running.

Main Methods:

• Simulated running and skipping gait cycles using OpenSim software for 5 adult participants.
• Collected motion capture data at a consistent speed (2.5 m/s) on an instrumented treadmill.
• Performed segmental power analysis to quantify muscle contributions to vertical mechanical power and work.

Main Results:

• Muscles like gluteus maximus, vasti, and soleus performed higher vertical work in the skipping hop (Skip 1) via power generation to the trunk.
• This contrasts with power absorption observed during running (Run) and the skipping step (Skip 2).
• Lower muscle force impulses in Skip 1 were compensated by concentric contractions generating power, increasing metabolic cost.

Conclusions:

• Skipping utilizes concentric muscle contractions to generate power, propelling the center-of-mass (COM) upward.
• This power generation mechanism, distinct from the deceleration in running, leads to greater COM displacement and higher metabolic cost in skipping.
• Understanding segmental power flow reveals how skipping achieves greater vertical movement with different muscle engagement strategies than running.