The study by Armstrong et al. (1), investigating the effect of weight-bearing activity on diabetic foot ulcer risk, provides new information on the role of activity variability in foot ulcer risk and confirms the results of a cohort study published last year. In that study (2), which used 24-h physical activity diaries, every additional hour of daily weight-bearing activity was associated with a 23% reduction in the risk of subsequent foot ulceration.

The approach used by Armstrong et al. to assess “the number of steps taken over a period of time,” may not have sufficiently captured the critical elements of weight-bearing activity that place those with diabetic peripheral neuropathy at increased risk of foot ulcers. Waist-mounted accelerometers, such as the Biotrainer they used, may not detect short shuffling steps characteristic of this population (3). Other important parameters include time per day spent weight bearing, the intensity of activity during the day, or the combination of weight bearing and dynamic plantar pressure (the “pressure-time integral,” an indicator of plantar tissue stress) (4). Secondly, while they excluded those with peripheral vascular disease, their use of nonparametric statistical tests made it impossible to adjust statistically for the effect of other characteristics that could potentially confound the association between activity and foot ulceration risk (5).

This study nonetheless should provoke a re-examination of the effect of weight-bearing activity on diabetic foot ulcer risk, in particular questioning the traditional clinical belief that weight-bearing activity should be discouraged categorically in this population. While we agree with the speculation by Armstrong et al. that “modulating the ‘peaks and valleys’ of activity in this population through some form of feedback might prove to reduce the risk for ulceration in this very-high-risk population,” another approach to reduce foot ulcer risk may be to promote a carefully “dosed” increase in weight-bearing activity that allows plantar tissues to adapt to increasing loads gradually (6). Further studies are needed to test this hypothesis and investigate the role of weight-bearing activity in plantar tissue adaptation, using technology (which needs to be developed and validated) that measures the pressure-time integral continuously.

Armstrong DG, Lavery LA, Holtz-Neiderer K, Mohler MJ, Wendel CS, Nixon BP, Boulton AJ: Variability in activity may precede diabetic foot ulceration.
Diabetes Care
LeMaster JW, Reiber GE, Smith DG, Heagerty PJ, Wallace C: Daily weight-bearing activity does not increase the risk of diabetic foot ulcers.
Med Sci Sports Exerc
Tudor-Locke CE, Myers AM: Challenges and opportunities for measuring physical activity in sedentary adults.
Sports Med
Sauseng S, Kastenbauer T, Sokol G, Irsigler K: Estimation of risk for plantar foot ulceration in diabetic patients with neuropathy.
Diabetes Nutr Metab
Boyko EJ, Ahroni JH, Stensel V, Forsberg RC, Davignon DR, Smith DG: A prospective study of risk factors for diabetic foot ulcer: the Seattle Diabetic Foot Study.
Diabetes Care
Mueller MJ, Maluf KS: Tissue adaptation to physical stress: a proposed “Physical Stress Theory” to guide physical therapist practice, education, and research.
Phys Ther