Greater fatigability and motor unit discharge variability in human type 2 diabetes.

This study determined the discharge characteristics of motor units from two lower limb muscles before and after fatiguing exercise in people with type 2 diabetes (T2D) with no symptoms of polyneuropathy and activity-matched controls. Seventeen people with T2D (65.0 ± 5.6 years; 8 women) and 17 controls (63.6 ± 4.5 years; 8 women) performed: (a) intermittent, isometric contractions at 50% maximal voluntary isometric contraction (MVIC) sustained to failure with the ankle dorsiflexors, and (b) a dynamic fatiguing task (30% MVIC load) for 6 min with the knee extensors. Before and after the fatiguing tasks, motor unit characteristics (including coefficient of variation (CV) of interspike intervals (ISI)) were quantified from high-density electromyography and muscle contractile properties were assessed via electrical stimulation. Fatigability was ~50% greater for people with T2D than controls for the dorsiflexors (time-to-failure: 7.3 ± 4.1 vs. 14.3 ± 9.1 min, p = .010) and knee extensors (power reduction: 56.7 ± 11.9 vs. 31.5 ± 25.5%, p < .001). The CV of ISI was greater for the T2D than control group for the tibialis anterior (23.1 ± 11.0 vs. 21.3 ± 10.7%, p < .001) and vastus lateralis (27.8 ± 20.2 vs. 24.5 ± 16.1%, p = .011), but these differences did not change after the fatiguing exercises. People with T2D had greater reductions in the electrically evoked twitch amplitude of the dorsiflexors (8.5 ± 5.1 vs. 4.0 ± 3.4%·min-1 , p = .013) and knee extensors (49.1 ± 10.0 vs. 31.8 ± 15.9%, p = .004) than controls. Although motor unit activity was more variable in people with T2D than controls, the greater fatigability of the T2D group for lower limb muscles was due to mechanisms involving disruption of contractile function of the exercising muscles rather than motor unit behavior.

Increased Cardiovascular Response to a 6-Minute Walk Test in People With Type 2 Diabetes.

BACKGROUND AND OBJECTIVE: Exercise is a cornerstone of management for type 2 diabetes; however, little is known about the cardiovascular (CV) response to submaximal functional exercise in people with type 2 diabetes. The aim of this study was to compare performance and CV response during a 6-minute walk test (6MWT) between people with type 2 diabetes and matched control subjects. METHODS: CV response and distance walked during the 6MWT were assessed in 30 people with type 2 diabetes, matched for age, body composition, physical activity, and estimated aerobic capacity with 34 control subjects (type 2 diabetes group: 16 men, 59.8 ± 8.8 years of age, 33.3 ± 10.9% body fat, physical activity of 7,968 ± 3,236 steps·day-1, estimated aerobic capacity 31.9 ± 11.1 mLO2·kg-1·min-1; control group: 19 men, 59.3 ± 8.8 years of age, 32.7 ± 8.5% body fat, physical activity 8,228 ± 2,941 steps·day-1, estimated aerobic capacity 34.9 ± 15.4 mLO2·kg-1·min-1). RESULTS: People with type 2 diabetes walked a similar distance (590 ± 75 vs. 605 ± 69 m; P = 0.458) compared with control subjects during the 6MWT and had similar ratings of perceived exertion (RPE) after the 6MWT (4.19 ± 1.56 vs. 3.65 ± 1.54, P = 0.147). However, at the end of the 6MWT, people with type 2 diabetes had a higher heart rate (108 ± 23 vs. 95 ± 18 beats·min-1; P = 0.048), systolic blood pressure (169 ± 26 vs. 147 ± 22 mmHg, P = 0.003), and rate-pressure product (18,762 ± 5,936 vs. 14,252 ± 4,330, P = 0.009) than control subjects. CONCLUSION: Although people with type 2 diabetes had similar performance and RPE during the 6MWT compared with control subjects, the CV response was greater for people with type 2 diabetes, indicating greater cardiac effort for similar perceived effort and performance of 6MWT. These data suggest that observation and prescription of exercise intensity should include both perceived effort and CV response.