Michael J Mckenna

Victoria University Melbourne | VU · Institute for Health and Sport

We investigated acute effects of the Na⁺,K⁺‐ATPase (NKA) inhibitor, digoxin, on muscle NKA content and isoforms, arterial plasma [K⁺] ([K⁺]a) and fatigue with intense exercise. In a randomised, crossover, double‐blind design, 10 healthy adults ingested 0.50 mg digoxin (DIG) or placebo (CON) 60 min before cycling for 1 min at 60% V̇O2peak${{\dot{V}}...

In muscle, digoxin inhibits Na⁺,K⁺‐ATPase (NKA) whereas acute exercise can increase NKA gene expression, consistent with training‐induced increased NKA content. We investigated whether oral digoxin increased NKA isoform mRNA expression (qPCR) in muscle at rest, during and post‐exercise in 10 healthy adults, who received digoxin (DIG, 0.25 mg per da...

Osteoarthritis is a leading cause of chronic pain and is associated with high rates of depression. Physical activity reduces depression symptoms and pain levels. It remains unknown if physical activity is associated with lower symptoms of depression irrespective of pain levels in individuals with osteoarthritis. We explored whether pain mediated or...

This historical review traces key discoveries regarding K⁺ and Na⁺ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na⁺,K⁺-ATPase (NKA) and exercise effects on plasma [K⁺] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal m...

Alexander Tacey, Jack Behne, Rhiannon K Patten, Minh Truc Ngo, Rees Thomas, Jessica Ancilleri, Chelsea Bone, Angela Paredes Castro, Helen McCarthy, Katherine Harkin, Julia FM Gilmartin-Thomas, Amir Takla, Calum Downie, Jane Mulcahy, Michelle Ball, Jenny Sharples, Sarah Dash, Amy Lawton, Breanna Wright, Peter Sleeth, Tina Kostecki, Christopher Sonn,...

Perturbations in K⁺ have long been considered a key factor in skeletal muscle fatigue. However, the exercise-induced changes in K⁺ intra-to-extracellular gradient is by itself insufficiently large to be a major cause for the force decrease during fatigue unless combined to other ion gradient changes such as for Na⁺. Whilst several studies described...

Background: Musculoskeletal conditions, including osteoarthritis (OA), are a leading cause of disability and chronic pain, and are associated with high rates of comorbid depression. However, signs of depression are often masked by pain. The aim of this study was to determine the prevalence and severity of depression and pain in individuals awaitin...

Background Osteoarthritis (OA) is a chronic, progressive condition that can be effectively managed via conservative treatments including exercise, weight management and education. Offering these treatments contemporaneously and digitally may increase adherence and engagement due to the flexibility and cost-effectiveness of digital program delivery....

BACKGROUND The demand for orthopaedic specialist consultation for patients with osteoarthritis (OA) in public hospitals is large and continues to grow. Lengthy wait times are increasingly affecting patients from low socioeconomic and culturally and linguistically diverse (CALD) backgrounds who are more likely to rely on public health care. OBJECTI...

Background The demand for orthopedic specialist consultations for patients with osteoarthritis in public hospitals is high and continues to grow. Lengthy waiting times are increasingly affecting patients from low socioeconomic and culturally and linguistically diverse backgrounds who are more likely to rely on public health care. Objective This st...

We investigated whether digoxin lowered muscle Na⁺,K⁺‐ATPase (NKA), impaired muscle performance and exacerbated exercise K⁺ disturbances. Ten healthy adults ingested digoxin (0.25 mg; DIG) or placebo (CON) for 14 days and performed quadriceps strength and fatiguability, finger flexion (FF, 105%peak‐workrate, 3 × 1 min, fourth bout to fatigue) and l...

Objective Time spent waiting for access to orthopaedic specialist health services has been suggested to result in increased pain in individuals with osteoarthritis (OA). We assessed whether time spent on an orthopaedic waiting list resulted in a detrimental effect on pain outcome measures in patients with knee or hip OA. Methods We searched Ovid M...

Purpose The cardiac T-wave peak-to-end interval (Tpe) is thought to reflect dispersion in ventricular repolarisation, with abnormalities in Tpe associated with increased risk of arrhythmia. Extracellular K⁺ modulates cardiac repolarisation, and since arterial plasma K⁺ concentration ([K⁺]) rapidly increases during and declines following exercise, w...

Based on a comprehensive review and critical analysis of the literature regarding the effects of sodium bicarbonate supplementation on exercise performance, conducted by experts in the field and selected members of the International Society of Sports Nutrition (ISSN), the following conclusions represent the official Position of the Society: 1. Sup...

Aim: We investigated whether acute carbohydrate ingestion reduced arterial potassium concentration ([K+ ]) during and after intense exercise and delayed fatigue. Methods: In a randomized, double-blind crossover design, eight males ingested 300 ml water containing 75 g glucose (CHO) or placebo (CON); rested for 60 min, then performed high-intensi...

PurposeThe Na+, K+-ATPase (NKA) is important in regulating trans-membrane ion gradients, cellular excitability and muscle function. We investigated the effects of resistance training in healthy young adults on the adaptability of NKA content and of the specific α and β isoforms in human skeletal muscle.Methods Twenty-one healthy young males (22.9 ±...

In vitro studies have shown that alterations in redox state can cause a range of opposing effects on the properties of the contractile apparatus in skeletal muscle fibers. To test whether and how redox changes occurring in vivo affect the contractile properties, vastus lateralis muscle fibers from seven healthy young adults were examined at rest (P...

We investigated the effects of testosterone suppression, hindlimb immobilization and recovery on skeletal muscle Na ⁺ ,K ⁺ -ATPase (NKA), measured via [ ³ H]ouabain binding site content (OB) and isoform abundances (α 1-3 , β 1-2 ). Male rats underwent Castration or Sham surgery plus 7 d rest, 10 d unilateral immobilization (cast) and 14 d recovery,...

Physical inactivity is a global health risk that can be addressed through application of exercise training suitable for an individual's health and age. People's willingness to participate in physical activity is often limited by an initially poor physical capability and early onset of fatigue. One factor associated with muscle fatigue during intens...

Objective Heat shock proteins (HSPs) are ubiquitously expressed proteins that help preserve cellular homeostasis. Within mammalian skeletal muscle three of the better characterised HSPs are HSP72, HSP27 and αB-crystallin. Among other roles, these three HSPs are involved in regulation of muscle mass and function and may be of importance in ageing. H...

Effects of regular use of cold-water immersion (CWI) on fiber type-specific adaptations in muscle K+ transport proteins to intense training, along with their relationship to changes in mRNA levels after the first training session, were investigated in humans. Nineteen recreationally-active men (24 ± 6 y, 79.5 ± 10.8 kg, 44.6 ± 5.8 mL∙kg-1∙min-1) co...

Intense exercise induces pronounced hyperkalemia, followed by transient hypokalemia in recovery. We investigated whether the β2-agonist salbutamol attenuated the exercise-hyperkalemia, and exacerbated the post-exercise hypokalemia, and whether hypokalemia was associated with impaired cardiac repolarization (QT hysteresis). Eleven healthy adults par...

We investigated the effect of a session of sprint-interval exercise on the mRNA content of NKA isoforms (α1-3, β1-3) and FXYD1 in human skeletal muscle. To explore some of the cellular stressors involved in this regulation, we evaluated the association between these mRNA responses and those of the transcription factors Sp1, Sp3 and HIF-1α. Given co...

Young adults typically adapt to intense exercise training with an increased skeletal muscle Na+,K+-ATPase (NKA) content, concomitant with reduced extracellular potassium concentration [K+] during exercise and enhanced exercise performance. Whether these changes with longitudinal training occur in older adults is unknown and was investigated here. F...

Keypoints summary: Ageing is associated with an upregulation of mitochondrial dynamics proteins, mitofusin 2 (Mfn2) and mitochondrial dynamics protein 49 (MiD49) in human skeletal muscle, the increased abundance of Mfn2 is exclusive to Type II muscle fibres. These changes occur despite a similar content of mitochondria, as measured by COXIV, NDUFA...

PurposeSalbutamol inhalation is permissible by WADA in athletic competition for asthma management and affects potassium regulation, which is vital for muscle function. Salbutamol effects on arterial potassium concentration ([K+]a) during and after high-intensity continuous exercise (HIcont) and intermittent exercise comprising repeated, brief sprin...

Physical training increases skeletal muscle Na(+),K(+)-ATPase (NKA) and improves exercise performance, but the effects of inactivity per se on NKA in human muscle are unknown. We investigated the effects of 23-days unilateral lower limb suspension (ULLS) and subsequent 4-weeks resistance training (RT) on muscle function and NKA in six healthy adult...

The maintenance of transmembrane Na⁺ and K⁺ concentration gradients and membrane potential is vital for the production of force in skeletal muscle. In aging an inability to maintain ion regulation and membrane potential would have adverse consequences on the capacity for performing repeated muscle contractions, which are critical for everyday activ...

Inactivity negatively impacts on skeletal muscle function mainly through muscle atrophy. However, recent evidence suggests that the quality of individual muscle fibers is also altered. This study examined the effects of 23 days of unilateral lower limb suspension (ULLS) on specific force and sarcoplasmic reticulum (SR) Ca2+ content in individual sk...

Na(+), K(+)-ATPase (NKA) isoforms (α1,α2,α3,β1,β2,β3) are involved in the maintenance of membrane potential and hence are important regulators of cellular homeostasis. Given the age-related decline in skeletal muscle function, we investigated whether the natural physiological process of aging is associated with altered abundance of NKA isoforms (α1...

Key points: The amount of Ca(2+) stored in the sarcoplasmic reticulum (SR) of muscle fibres is decreased in aged individuals, and an important question is whether this results from increased Ca(2+) leakage out through the Ca(2+) release channels (ryanodine receptors; RyRs). The present study examined the effects of blocking the RyRs with Mg(2+), o...

This study examined the contractile properties and sarcoplasmic reticulum (SR) Ca(2+) content in mechanically skinned vastus lateralis muscle fibres of Old (70 ± 4 yrs) and Young (22 ± 3 yrs) humans to investigate whether changes in muscle fibre properties contribute to muscle weakness in old age. In type II fibres of Old subjects, specific force w...

While training upregulates skeletal muscle Na + , K +-ATPase (NKA), the effects of knee injury and associated disuse on muscle NKA remain unknown. This was therefore investigated in six healthy young adults with a torn anterior cruciate ligament, (KI; four females, two males; age 25.0 AE 4.9 years; injury duration 15 AE 17 weeks; mean AE SD) and se...

Abstract The punt kick is a fundamental skill used in several team sports; however, there has been a lack of research on how fatigue affects its technique. The purpose of this study was to determine the effects of short-term fatigue on punt-kicking performance. Eight elite and sub-elite Australian Football players performed maximal drop punt kicks...

The Na(+), K(+)-ATPase (NKA) plays a key role in muscle excitability, but little is known in human skeletal muscle about fiber-type specific differences in NKA isoform expression or adaptability. A vastus lateralis muscle biopsy was taken in 17 healthy young adults to contrast NKA isoform protein relative abundance between type I and IIa fibers. We...

The Na+,K+-ATPase (NKA) plays a fundamental role in the regulation of skeletal muscle membrane Na+ and K+ gradients, excitability and fatigue during repeated intense contractions. Many studies have investigated the effects of acute concentric exercise on K+ regulation and skeletal muscle NKA, but almost nothing is known about the effects of repeate...

We investigated whether potassium (K(+)) disturbances during and following intense exercise may be pronounced when utilising a large contracting muscle mass, examining maximal 2000m rowing exercise effects on radial arterial plasma K(+) concentration ([K(+)]a) in 11 healthy adults. Blood was sampled at baseline, pre-exercise, each 30 s during rowin...

Exercise elicits skeletal-muscle adaptations which are important for improved health outcomes. We compared the effects of a futsal game (FUT) and moderate-intensity continuous exercise (MOD), on the skeletal-muscle protein signalling responses in young, healthy individuals. 16 men undertook an incremental exercise test and a resting muscle biopsy p...

Objectives: To measure the activity profile, hydration status and core temperature of elite team sport athletes during matches in hot and cool conditions. Design: Thirty-five professional Australian footballers (age 25.9 ± 3.5 yrs; height 188.4 ± 7.8 cm; body mass 90.6 ± 8.8 kg), gave informed consent to participate in this study. Core temperatu...

Key points Release and uptake of Ca ²⁺ ions by the sarcoplasmic reticulum (SR) regulates contraction in skeletal muscle. SR Ca ²⁺ uptake and leak properties in human muscle are presently not well defined. The surface membrane of individual human muscle fibres was removed by microdissection, and the rate of SR Ca ²⁺ uptake at different applied [Ca ²...

Skeletal muscle fibre specialization is a critical step towards the optimization of the contractile performance. Molecular structure and functional parameters differ among muscle fibres to obtain the best response to specific functional demands. This versatile diversity has been developed during phylogenesis and evolution, but further refinement st...

Key points Skeletal muscle calcium resequestration and performance is increased in male rats with induced diabetes; and whilst muscle calcium resequestration is important during exercise, it has not been investigated in human diabetes or compared between sexes. We show that Ca ²⁺ ‐ATPase activity and Ca ²⁺ uptake are higher among people with type 1...

The relationship between sarcoplasmic reticulum (SR) Ca(2+) content and calsequestrin (CSQ) isoforms was investigated in human skeletal muscle. A fibre lysing assay was used to quantify the endogenous Ca(2+) content and maximal Ca(2+) capacity of the SR in skinned segments of type I and type II fibres from vastus lateralis muscles of young healthy...

Knee osteoarthritis is a debilitating disorder prevalent in older populations that is accompanied by declines in muscle mass, strength, and physical activity. In skeletal muscle, the Na(+),K(+)-pump (NKA) is pivotal in ion homeostasis and excitability, and is modulated by disuse and exercise training. This study examined the effects of osteoarthrit...

Introduction: Knee osteoarthritis (OA) is a debilitating disorder that is accompanied by loss of muscle mass and strength and is prevalent in older populations (Lawrence et al., 2008). In skeletal muscle the Na+,K+ -ATPase (NKA) regulates membrane potential and excitability and thereby directly influences skeletal muscle force generation (McKenna e...

Introduction: Knee osteoarthritis (OA) is a debilitating disorder that is accompanied by loss of muscle mass and strength and is prevalent in older populations (Lawrence et al., 2008). In skeletal muscle the Na+,K+ -ATPase (NKA) regulates membrane potential and excitability and thereby directly influences skeletal muscle force generation (McKenna e...

The authors investigated the efficacy of a single exposure to 14 min of cold-water immersion (COLD) and contrast water therapy (CWT) on posttraining recovery in Australian football (AF). Fourteen AF players participated in 3 wk of standardized training. After week 1 training, all players completed a passive recovery (PAS). During week 2, COLD or CW...

Purpose: The efficacy of a single exposure to 14 min of contrast water therapy (CWT) or cold-water immersion (COLD) on recovery postmatch in elite professional footballers was investigated. Method: Twenty-four elite footballers participated in a match followed by 1 of 3 recovery interventions. Recovery was monitored for 48 h postmatch. Repeat-sp...

Aging is associated with reduced muscle mass, weakness and increased fatigability. In skeletal muscle, the Na(+),K(+)-pump (NKA) is important in regulating Na(+)/K(+) gradients, membrane excitability and contractility, but the effects of aging on NKA are unclear. We investigated whether aging is linked with reduced muscle NKA by contrasting muscle...

New findings What is the central question of this study? Are exercise‐induced changes in metabolites and ions a crucial factor in the adaptation of contracting muscle? This was assessed by manipulating the rest period between high‐intensity intervals. What is the main finding and its importance? Our results suggest that the perturbation of muscle m...

Older adults have an increase in circulating markers of inflammation. The current study examined whether there is an increase in the expression of inflammatory markers within the vastus lateralis, a major locomotive muscle, of older adults, and if so, whether the reduction in muscle strength and aerobic capacity in older adults is related to increa...

Organ transplantation is one of the medical miracles or the 20th century. It has the capacity to substantially improve exercise performance and quality of life in patients who are severely limited with chronic organ failure. We focus on the most commonly performed solid-organ transplants and describe peak exercise performance following recovery fro...

TO THE EDITOR: It is well accepted that muscle Na�-K�-ATPase activity is increased with contraction/exercise (5), therefore this Viewpoint debate changes in the maximal Na�-K�- ATPase activity (2). In proposing increased maximal Na�-K�- ATPase activity with contractions, Juel (2) fails to note several important points. We have utilized whole muscle...

Key points Reactive oxygen‐based molecules generated within muscle fibres in both exercise and pathological conditions can greatly affect muscle function. These and consequent reactions can lead to either decreased or increased force response by the contractile proteins, but the mechanisms are unknown. This study demonstrates that the increase in...

A fully automated impact sensing system (AISS) is being developed in an effort to overcome scoring controversies that have beset amateur boxing throughout its history. The AISS uses subtly modified boxing equipment that incorporates ‘smart’ fabrics. An impact is detected when an electrically conductive region on a glove connects with an electricall...

There is considerable interest in potential ergogenic and therapeutic effects of increasing skeletal muscle carnosine content, although its effects on excitation-contraction (EC) coupling in human muscle have not been defined. Consequently, we sought to characterize what effects carnosine, at levels attained by supplementation, has on human muscle...

Objective Patients with knee osteoarthritis (OA) are characterized by increased muscle inflammation and altered gait. We investigated the association between proinflammatory mediators in the vastus lateralis and physical function and gait in patients with knee OA.Methods Nineteen patients with knee OA underwent gait analysis, assessment of self-rep...

We investigated the effects of acute and chronic repeated-sprint exercise (RSE) on the skeletal muscle messenger RNA (mRNA) expression and protein abundance/phosphorylation associated with mitochondrial biogenesis. Ten healthy young adults (seven males, three females) performed the RSE trial, comprising three sets of 5 × 4-s maximal sprints on a no...

We examined whether abnormal skeletal muscle Na(+),K(+)-pumps underlie impaired exercise performance in haemodialysis patients (HDP) and whether these are improved in renal transplant recipients (RTx). Peak oxygen consumption ( O(2peak)) and plasma [K(+)] were measured during incremental exercise in 9RTx, 10 HDP and 10 healthy controls (CON). Quadr...