Lack of independent effect of type 2 diabetes beyond characteristic comorbidities and medications on small muscle mass exercising muscle blood flow and exercise tolerance

Abstract

Persons with type 2 diabetes (T2D) are believed to have reduced exercise tolerance; this may be partly due to impaired exercising muscle blood flow (MBF). Whether there is an impact of T2D on exercising MBF within the typical constellation of comorbidities (hypertension, dyslipidemia, obesity) and their associated medications has not been investigated. We tested the hypothesis that small muscle mass exercise tolerance is reduced in persons with T2D versus Controls (matched for age, body mass index, fitness, comorbidities, non-T2D medications) and that this is related to blunted MBF. Eight persons with T2D and eight controls completed a forearm critical force (fCFimpulse) test as a measure of exercise tolerance (10-min intermittent maximal effort forearm contractions; the average contraction impulse in the last 30 sec quantified fCFimpulse). Forearm blood flow (FBF; ultrasound) and mean arterial pressure (MAP; finger photoplethysmography) were measured; forearm vascular conductance (FVK) was calculated. Data are means ± SD, T2D versus Control. fCFimpulse was not different between groups (136.9 ± 47.3 N·sec vs. 163.1 ± 49.7 N·sec, P = 0.371) nor was the ΔFBF from rest to during exercise at fCFimpulse (502.9 ± 144.6 vs. 709.1 ± 289.2 mL/min, P = 0.092), or its determinants ΔFVK and ΔMAP (both P > 0.05), although there was considerable interindividual variability. ΔFBF was strongly related to fCFimpulse (r = 0.727, P = 0.002), providing support for the relationship between oxygen delivery and exercise tolerance. We conclude that small muscle mass exercising MBF and exercise tolerance are not impaired in representative persons with T2D versus appropriately matched controls. This suggests that peripheral vascular control impairment does not contribute to reduced exercise tolerance in this population.

Neurovascular Dysregulation During Exercise in Type 2 Diabetes

“…Similarly, a more recent study (Groen et al, 2019) reported attenuated increases in leg BF and vascular conductance in T2D patients during single-leg knee extension exercise. However, it should be noted that conflicting findings have also been reported (Martin et al, 1995;Copp et al, 2010;Poitras et al, 2015). For example, Poitras et al (2015) found similar increases in forearm muscle BF during a forearm critical force test in T2D patients and controls.…”

“…However, it should be noted that conflicting findings have also been reported (Martin et al, 1995;Copp et al, 2010;Poitras et al, 2015). For example, Poitras et al (2015) found similar increases in forearm muscle BF during a forearm critical force test in T2D patients and controls. Nonetheless, there are substantial data reporting that T2D significantly impacts the ability to properly adjust the circulation during exercise, leading to an augmented BP and reduced contracting skeletal muscle BF.…”

Quantification of Mitochondrial Oxidative Phosphorylation in Metabolic Disease: Application to Type 2 Diabetes

“…This ultimately results in reduced net glucose disposal and increased risk for cardiovascular disease, blindness, renal failure, nerve damage, loss of limb, and other co-morbidities [8,9]. Exercise intolerance, defined as a susceptibility to fatigue or reduced exercise capacity (VO 2Max ), has also been a disputed co-morbidity of this disease [10,11,12,13,14,15,16,17]. Skeletal muscle accounts for ~80% of glucose uptake during an insulin clamp [18] and can increase from resting levels anywhere from 20-fold (~0.25 mM/min → ~4 mM/min single leg [19]) to 50-fold [20] during exercise [19,21,22].…”

Insight into type 2 diabetes impaired exercising mitochondrial oxidative flux: is it blood flow, mitochondria, or neither?

“…convective O 2 delivery) impairments. However, studies have shown that muscle blood flow during small muscle mass exercise does not differ in persons with T2D when compared to individuals without T2D, but who shared traditional comorbidities (Poitras et al 2015). In…”

“…However, studies have shown that muscle blood flow during small muscle mass exercise does not differ in persons with T2D when compared to individuals without T2D, but who shared traditional comorbidities (Poitras et al . 2015). In the current study, the delivery of O 2 to skeletal muscle, indicated by gastrocnemius blood flow, total haemoglobin, and oxyhaemoglobin, did not differ between groups at baseline or post‐SLET.…”