Biomechanics and the metabolic cost of walking in people with diabetes

Petrovic, Milos (2016) Biomechanics and the metabolic cost of walking in people with diabetes. Doctoral thesis (PhD), Manchester Metropolitan University and KU Leuven.

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Abstract

Diabetes mellitus is a serious worldwide disease characterised by pathological metabolism of sugars. Diabetic peripheral neuropathy (DPN) is a common complication of diabetes involving dysfunction of peripheral nerves. Diabetes is known to alter a number of biomechanical aspects of gait, but it remains unknown as to whether these alterations could impact upon the metabolic cost of walking (CoW). The aim of this thesis was to investigate the CoW in people with diabetes and examine biomechanical factors that could contribute to explaining any potential differences. Data were generated from three groups: patients with DPN (n=14), patients with diabetes but without peripheral neuropathy (DM, n=22), and controls without diabetes (Ctrl, n=31). Gait assessment was performed using a Vicon motion analysis system and Kistler force plates while participants walked at a range of matched speeds (between 0.6 and 1.6 m/s). Oxygen consumption was measured continuously whilst participants walked on a motor-driven treadmill at the range of matched walking speeds. Ultrasonographic imaging data from the plantarflexor muscle-tendon complex (MTC) were collected in vivo during walking to determine MTC properties. Magnetic resonance imaging of the ankle joint in the standing position was used to quantify the internal leverage around the ankle. Isometric plantarflexor maximal voluntary contraction strength was measured using a dynamometer. The CoW was significantly higher in the DPN group across a range of matched walking speeds and also in the DM group at selected speeds, compared to Ctrl. Despite the higher CoW in patients with diabetes, concentric lower limb joint work was significantly lower in DM and DPN groups compared to Ctrl. A greater value for the effective mechanical advantage (EMA) at the ankle joint was found in the DPN and DM groups compared to Ctrl, meaning that the ankle plantarflexor muscles developed relatively lower forces to generate a given joint moment compared to Ctrl. The increased EMA was mainly caused by a smaller external moment arm of the ground reaction force in the DPN and DM groups compared to Ctrl. The DPN group reduced the joint moment at the ankle during walking by applying the ground reaction force more proximally on the foot, or at an angle directed more towards the ankle, thereby reducing the external moment arm and increasing the EMA around the ankle. The DPN group demonstrated significantly less Achilles tendon elongation during walking, higher stiffness and higher hysteresis compared to Ctrl. These properties mean that the Achilles tendon would store and release less energy in the DPN group during walking, requiring more work from the plantarflexor muscles. Vertical displacement of the centre of mass during walking was not different between groups and is therefore unlikely to be a factor in itself that contributes towards the increased CoW in people with diabetic neuropathy. A higher cumulative joint work resulting from an increased cadence may contribute to the higher CoW in patients with diabetes, along with a reduced elastic energy contribution from the Achilles tendon.