Hemodynamic responses during graded and constant-load plantar flexion exercise in middle-aged men and women with type 2 diabetes

Abstract

Kiely C, O'Connor E, O'Shea D, Green S, Egaña M. Hemodynamic responses during graded and constant-load plantar flexion exercise in middle-aged men and women with type 2 diabetes. J Appl Physiol 117: 755-764, 2014. First published August 14, 2014 doi:10.1152/japplphysiol.00555.2014.-We tested the hypotheses that type 2 diabetes (T2D) impairs the 1) leg hemodynamic responses to an incremental intermittent plantar-flexion exercise and 2) dynamic responses of leg vascular conductance (LVC) during low-intensity (30% maximal voluntary contraction, MVC) and high-intensity (70% MVC) constant-load plantar-flexion exercise in the supine posture. Forty-four middle-aged individuals with T2D (14 women), and 35 healthy nondiabetic (ND) individuals (18 women) were tested. Leg blood flow (LBF) was measured between each contraction using venous occlusion plethysmography. During the incremental test peak force (Fpeak) relative to MVC was significantly reduced (P Ͻ 0.05) in men and women with T2D compared with their respective nondiabetic counterparts. Peak LBF and the slope of LBF relative to percentage F peak were also reduced (P Ͻ 0.05) in women with T2D compared with healthy women (peak blood flow, 460.6 Ϯ 126.8 vs. 628.3 Ϯ 347.7 ml/min; slope, 3.78 Ϯ 1.74 vs. 5.85 Ϯ 3.14 ml·min Ϫ1 · %Fpeak Ϫ1 ) and in men with T2D compared with nondiabetic men (peak blood flow, 621.7 Ϯ 241.3 vs. 721.2 Ϯ 359.7 ml/min; slope, 5.75 Ϯ 2.66 vs. 6.33 Ϯ 3.63 ml·min Ϫ1 ·%Fpeak Ϫ1 ). During constantload contractions at 30% MVC T2D did not affect the dynamic responses of LVC (LBF/MAP). However, at 70% MVC [completed by a subgroup of participants (20 with T2D, 6 women; 13 ND, 6 women)] the time constant of the second growth phase of LVC was longer and the amplitude of the first growth phase was lower (P Ͻ 0.05 for both) in men and women with T2D. The results suggest that the T2D-induced impairments in performance of the leg muscles are related to reductions in blood flow in both men and women. vascular conductance; blood flow; type 2 diabetes; muscle; exercise EXERCISE INTOLERANCE IS A major complication of type 2 diabetes (T2D) that is associated with worsening of cardiovascular outcomes and increased risk of mortality (45). Although the etiology of exercise intolerance in T2D is still not well understood, peak oxygen uptake (V O 2 ) responses to a graded exercise are reduced in men and women with T2D compared with nondiabetic healthy peers (16,19,25,34), and the rate of increase in V O 2 (V O 2 kinetics) is slowed in younger and middle-aged men and women with T2D (1,3,19,25,34) but not in older men with this disease (47). In healthy individuals, V O 2 kinetics during cycling exercise are limited by the muscle's oxidative capacity rather than O 2 delivery per se (30); however, it is likely that in patients with T2D, V O 2 kinetics are limited, at least in part, by reduced O 2 delivery to the contracting muscle.Support for reduced O 2 delivery as the source of the impairment in V O 2 control can be found in reports showing significantly slower heavy in...

Effect of obesity on oxygen uptake and cardiovascular dynamics during whole-body and leg exercise in adult males and females

“…Measurements of these systemic responses might shed light on whether BMI-related changes in _ VO 2 dynamics are related to systemic rates of O 2 delivery and/ or O 2 utilization. However, as we observed in patients with type 2 diabetes (MacAnaney et al 2011;O'Connor et al 2012;Kiely et al 2014), it is also possible that a slowing in _ VO 2 dynamics is not explained by such systemic measurements but are associated with impaired responses of vasodilation measured in contracting muscles.…”

“…), older healthy individuals (Reeder and Green ), as well as middle‐aged subjects with type 2 diabetes (Kiely et al. ). This same structure was observed in the present cohort and, because the fourth phase was not observed in all subjects, our analyses were restricted to the first three phases.…”

“…On a subsequent day, subjects performed three bouts of intermittent contractions (2 sec contraction, 4 sec relaxation) at 30%MVC with 10 min rest periods in between bouts (Egaña and Green ; Kiely et al. ). This intensity corresponds to approximately 50% of the peak force achieved during an incremental protocol, does not evoke a third growth phase observed at higher forces (Reeder and Green ), and it can be sustained with a minimal rate of fatigue over 30 min (Egaña and Green ).…”

“…), as well as its verification in older healthy subjects and overweight and obese subjects with type 2 diabetes (Kiely et al. ), these averaged, individual responses were fitted to the following function,where A 0 is the baseline response immediately prior to the initial contraction, A 1 –A 4 are amplitudes, TD 1 –TD 4 are time delays, and τ 1 – τ 4 are time constants of the first (rapid growth), second (rapid decay), third (slow growth), and fourth (slow decay) phases, respectively. The parameters F1–F4 are conditional expressions that limit the fitting of a particular phase to the period at and beyond the time delay associated with that phase.…”

“…; Kiely et al. ), it is also possible that a slowing in O 2 dynamics is not explained by such systemic measurements but are associated with impaired responses of vasodilation measured in contracting muscles.…”