Soft Tissue Deformations Contribute to the Mechanics of Walking in Obese Adults.
Obesity not only adds to the mass that must be carried during walking but also changes body composition. Although extra mass causes roughly proportional increases in musculoskeletal loading, less well understood is the effect of relatively soft and mechanically compliant adipose tissue.


OBJECTIVE
This purpose of this study was to estimate the work performed by soft tissue deformations during walking. The soft tissue would be expected to experience damped oscillations, particularly from high force transients after heel strike, and could potentially change the mechanical work demands for walking.


METHODS
We analyzed treadmill walking data at 1.25 m·s for 11 obese (BMI >30 kg·m) and nine nonobese (BMI <30 kg·m) adults. The soft tissue work was quantified with a method that compares the work performed by lower extremity joints as derived using assumptions of rigid body segments, with that estimated without rigid body assumptions.


RESULTS
Relative to body mass, obese and nonobese individuals perform similar amounts of mechanical work. However, negative work performed by soft tissues was significantly greater in obese individuals (P = 0.0102), equivalent to approximately 0.36 J·kg vs 0.27 J·kg in nonobese individuals. The negative (dissipative) work by soft tissues occurred mainly after heel strike and, for obese individuals, was comparable in magnitude to the total negative work from all of the joints combined (0.34 J·kg vs 0.33 J·kg for obese and nonobese adults, respectively). Although the joints performed a relatively similar amount of work overall, obese individuals performed less negative work actively at the knee.


CONCLUSIONS
The greater proportion of soft tissues in obese individuals results in substantial changes in the amount, location, and timing of work and may also affect metabolic energy expenditure during walking.
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI; 2Laboratory of Neuromotor Physiology, IRCCS Santa Lucia Foundation, Rome, ITALY; 3Department of Physical Medicine and Rehabilitation, Vanderbilt University, Nashville, TN; and 4Department of Health and Exercise Science, Colorado State University, Fort Collins, CO.
Xiao-Yu
XY
Fu
Karl E
KE
Zelik
Wayne J
WJ
Board
Raymond C
RC
Browning
Arthur D
AD
Kuo
D000273:Adipose Tissue / Q000503:physiopathology*; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007596:Joints / Q000503:physiopathology; D035002:Lower Extremity / Q000503:physiopathology; D008297:Male; D009765:Obesity / Q000503:physiopathology*; D005082:Physical Exertion / Q000502:physiology; D016138:Walking / Q000502:physiology*