Fat people walk funny.....

Sorry, bad title. This article notes that while obese people are often told to walk as exercise, their size and weight may mean that walking could be a potentially dangerous for them from a biomechanical perspective....so they walk more slowly to compensate. Interesting.

Effects of Obesity on the Biomechanics of Walking at Different Speeds.
APPLIED SCIENCES

Medicine & Science in Sports & Exercise. 39(9):1632-1641, September 2007.
BROWNING, RAYMOND C.; KRAM, RODGER
Abstract:
Purpose: Walking is a recommended form of exercise for the treatment of obesity, but walking may be a critical source of biomechanical loads that link obesity and musculoskeletal pathology, particularly knee osteoarthritis. We hypothesized that compared with normal-weight adults 1) obese adults would have greater absolute ground-reaction forces (GRF) during walking, but their GRF would be reduced at slower walking speeds; and 2) obese adults would have greater sagittal-plane absolute leg-joint moments at a given walking speed, but these moments would be reduced at slower walking speeds.

Methods: We measured GRF and recorded sagittal-plane kinematics of 20 adults (10 obese and 10 normal weight) as they walked on a level, force-measuring treadmill at six speeds (0.5-1.75 m[middle dot]s-1). We calculated sagittal-plane net muscle moments at the hip, knee, and ankle.

Results: Compared with their normal-weight peers, obese adults had much greater absolute GRF (N), stance-phase sagittal-plane net muscle moments (N[middle dot]m) and step width (m).

Conclusions: Greater sagittal-plane knee moments in the obese subjects suggest that they walked with greater knee-joint loads than normal-weight adults. Walking slower reduced GRF and net muscle moments and may be a risk-lowering strategy for obese adults who wish to walk for exercise. When obese subjects walked at 1.0 versus 1.5 m[middle dot]s-1, peak sagittal-plane knee moments were 45% less. Obese subjects walking at approximately 1.1 m[middle dot]s-1 would have the same absolute peak sagittal-plane knee net muscle moment as normal-weight subjects when they walk at their typical preferred speed of 1.4 m[middle dot]s-1.