Exercise-induced hyperemia is associated with knee extensor fatigability in adults with type 2 diabetes

Increased contribution of KCa channels to muscle contraction induced vascular and blood flow responses in sedentary and exercise trained ZFDM rats

KEY POINTS

Microvascular dysfunction in type 2 diabetes impairs blood flow redistribution during exercise and limits the performance of skeletal muscle and may cause early fatigability. Endothelium-dependent hyperpolarization (EDH), which mediates vasodilation in resistance arteries is known to be depressed in animals with diabetes. Here we report that low-intensity exercise training in ZFDM rats increased KCa channel-derived component in the vasodilator responses to muscle contraction than in sedentary rats, partly due to the increase in KCNN3 expression. These results suggest that low-intensity exercise training improves blood flow redistribution in contracting skeletal muscle in metabolic disease with diabetes via upregulation of EDH.

ABSTRACT

In resistance arteries, endothelium-dependent hyperpolarization (EDH) mediated vasodilation is depressed in diabetes. We hypothesized that downregulation of KCa channel derived EDH reduces exercise-induced vasodilation and blood flow redistribution in diabetes. To test this hypothesis, we evaluated vascular function in response to hindlimb muscle contraction, and the contribution of KCa channels in anaesthetised ZFDM, metabolic disease rats with type 2 diabetes. We also tested whether exercise training ameliorated the vascular response. Using in vivo microangiography, the hindlimb vasculature was visualized before and after rhythmic muscle contraction (0.5 s tetanus every 3 sec, 20 times) evoked by sciatic nerve stimulation (40 Hz). Femoral blood flow of the contracting hindlimb was simultaneously measured by an ultrasonic flowmeter. The contribution of KCa channels was investigated in the presence and absence of apamin and charybdotoxin. We found that vascular and blood flow responses to muscle contraction were significantly impaired at the level of small artery segments in ZFDM fa/fa rats compared to its lean control fa/+ rats. The contribution of KCa channels was also smaller in fa/fa than in fa/+ rats. Low-intensity exercise training for 12 weeks in fa/fa rats demonstrated minor changes in the vascular and blood flow response to muscle contraction. However, KCa-derived component in the response to muscle contraction was much greater in exercise trained than in sedentary fa/fa rats. These data suggest that exercise training increases the contribution of KCa channels among endothelium-dependent vasodilatory mechanisms to maintain vascular and blood flow responses to muscle contraction in this metabolic disease rat model. Abstract figure legend Low-intensity exercise training in ZFDM, metabolic disease rats with type 2 diabetes increases KCa channel-derived component of endothelium-dependent hyperpolarization in the vascular and blood flow responses to skeletal muscle contraction than the responses in sedentary rats, partly due to upregulation of KCNN3 protein expression. This article is protected by copyright. All rights reserved.

Morphological and functional changes in skeletal muscle in type 2 diabetes mellitus: A systematic review and meta-analysis

INTRODUCTION

Changes in the skeletal muscle are common in patients with type 2 diabetes mellitus (T2DM). These changes impair your motor skills.

OBJECTIVE

This systematic review aimed to investigate changes in skeletal muscle in patients with T2DM.

METHODS

The search was carried out in the PubMed, Scopus, and Web of Science databases until December 1, 2021. Observational studies that evaluated musculoskeletal changes in people with T2DM were included. The review was based on PRISMA recommendations. The primary parameters analyzed were muscle strength, muscle mass, muscle power, and muscle endurance.

RESULTS

Forty-eight studies were included, with a total of 26,042 participants. The results revealed that T2DM is associated with a reduction in handgrip [-2.64 (CI 95% = -3.33 to -1.95, Z = -7.50, p < .0001], and knee extension muscle strength [-0.56 (CI 95% = -0.76 to -0.36, Z = -5.64, p < .0001)], a higher percentage of type II fibers [11.74 (CI 95% = 6.24 to 17.25, Z = 4.18, p < .0001)], and a lower percentage of type I fibers [-15.69 (CI 95% = -18.22 to -13.16, Z = -12.16, p < .0001], in addition to a greater thickness of the calcaneus tendon (p < .0001).

CONCLUSION

Individuals with T2DM present skeletal muscle impairments, mainly reduced muscle strength, mass, and endurance; increase in the thickness of the calcaneus tendon, and alteration in the proportion of type I and II fibers, even in the initial stage of the disease.

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.

Neurovascular Dysregulation During Exercise in Type 2 Diabetes

Emerging evidence suggests that type 2 diabetes (T2D) may impair the ability to properly adjust the circulation during exercise with augmented blood pressure (BP) and an attenuated contracting skeletal muscle blood flow (BF) response being reported. This review provides a brief overview of the current understanding of these altered exercise responses in T2D and the potential underlying mechanisms, with an emphasis on the sympathetic nervous system and its regulation during exercise. The research presented support augmented sympathetic activation, heightened BP, reduced skeletal muscle BF, and impairment in the ability to attenuate sympathetically mediated vasoconstriction (i.e., functional sympatholysis) as potential drivers of neurovascular dysregulation during exercise in T2D. Furthermore, emerging evidence supporting a contribution of the exercise pressor reflex and central command is discussed along with proposed future directions for studies in this important area of research.

Greater Lower Limb Fatigability in People with Prediabetes than Controls

INTRODUCTION

The study purpose was to compare perceived fatigability and performance fatigability after high-velocity contractions with knee extensor muscles between people with prediabetes, people with type 2 diabetes (T2D), and controls without diabetes matched for age, body mass index, and physical activity.

METHODS

Twenty people with prediabetes (11 men, 9 women: 63.1 ± 6.0 yr, 26.9 ± 4.2 kg·m, 8030 ± 3110 steps per day), 39 with T2D (23 men, 16 women: 61.2 ± 8.5 yr, 29.4 ± 6.4 kg·m, 8440 ± 4220 steps per day), and 27 controls (13 men, 14 women: 58.1 ± 9.4 yr, 27.3 ± 4.3 kg·m, 8400 ± 3000 steps per day) completed the Fatigue Impact Scale as a measure of perceived fatigability and a fatigue protocol including 120 maximal-effort, high-velocity concentric contractions (MVCC; 1 contraction/3 s) with the knee extensors using a submaximal load (30% maximum) to quantify performance fatigability. Electrical stimulation was used to assess voluntary activation and contractile function of the knee extensor muscles before and after the fatigue protocol.

RESULTS

Fatigue Impact Scale scores were not different between people with prediabetes, people with T2D, and controls (12.5 ± 15.1, 18.3 ± 22.7, and 12.6 ± 18.6, respectively; P = 0.517). However, people with prediabetes had greater reductions in MVCC power during the fatigue protocol than did controls (31.8% ± 22.6% vs 22.1% ± 21.1%, P < 0.001), and both groups had lesser reductions than the T2D group (44.8% ± 21.9%, P < 0.001). Similarly, the prediabetes group had larger reductions in electrically evoked twitch amplitude than the control group (32.5% ± 24.9% vs 21.3% ± 33.0%, P < 0.001), but lesser reductions than those with T2D (44.0% ± 23.4%, P < 0.001). For all three groups, a greater decline in MVCC power was associated with larger reductions of twitch amplitude (r = 0.350, P < 0.001).

CONCLUSION

People with prediabetes have greater performance fatigability of the knee extensors due to contractile mechanisms compared with controls, although less performance fatigability than that of people with T2D.

Greater α1-adrenergic-mediated vasoconstriction in contracting skeletal muscle of patients with type 2 diabetes

Findings presented in this article are the first to show patients with type 2 diabetes mellitus have blunted hyperemic and vasodilatory responses to dynamic handgrip exercise. Moreover, we illustrate greater α1-adrenergic-mediated vasoconstriction may contribute to our initial observations. Collectively, these data suggest patients with type 2 diabetes may have impaired functional sympatholysis, which can contribute to their reduced exercise capacity.

Exaggerated exercise pressor reflex in type 2 diabetes: Potential role of oxidative stress

Type 2 diabetes mellitus (T2DM) leads to exaggerated cardiovascular responses to exercise, in part due to an exaggerated exercise pressor reflex. Accumulating data suggest excessive oxidative stress contributes to an exaggerated exercise pressor reflex in cardiovascular-related diseases. Excessive oxidative stress is also a primary underlying mechanism for the development and progression of T2DM. However, whether oxidative stress plays a role in mediating the exaggerated exercise pressor reflex in T2DM is not known. Therefore, this review explores the potential role of oxidative stress leading to increased activation of the afferent arm of the exercise pressor reflex. Several lines of evidence support direct and indirect effects of oxidative stress on the exercise pressor reflex. For example, intramuscular ROS may directly and indirectly (by attenuating contracting muscle blood flow) increase group III and IV afferent activity. Oxidative stress is a primary underlying mechanism for the development of neuropathic pain, which in turn is associated with increased group III and IV afferent activity. These are the same type of afferents that evoke muscle pain and the exercise pressor reflex. Furthermore, oxidative stress-induced release of inflammatory mediators may modulate afferent activity. Collectively, these alterations may result in a positive feedback loop that further amplifies the exercise pressor reflex. An exaggerated reflex increases the risk of adverse cardiovascular events. Thus, identifying the contribution of oxidative stress could provide a potential therapeutic target to reduce this risk in T2DM.