Niall M. Moyna

The acute versus the chronic response to exercise

PURPOSE There is strong and consistent evidence that a single exercise session can acutely reduce triglycerides and increase high-density lipoprotein (HDL) cholesterol (HDL-C), reduce blood pressure, and improve insulin sensitivity and glucose homeostasis. Such observations suggest that at least some of the effects on atherosclerotic cardiovascular disease (ASCVD) risk factors attributed to exercise training may be the result of recent exercise. RESULTS These acute and chronic exercise effects cannot be considered in isolation. Exercise training increases the capacity for exercise, thereby permitting more vigorous and/or more prolonged individual exercise sessions and a more significant acute effect. The intensity, duration, and energy expenditure required to produce these acute exercise effects are not clearly defined. The acute effect of exercise on triglycerides and HDL-C appears to increase with overall energy expenditure possibly because the effect maybe mediated by reductions in intramuscular triglycerides. Prolonged exercise appears necessary for an acute effect of exercise on low-density lipoprotein (LDL) cholesterol (LDL-C) levels. The acute effect of exercise on blood pressure is a low threshold phenomenon and has been observed after energy expenditures requiring only 40% maximal capacity. The acute effect of exercise on glucose metabolism appears to require exercise near 70% maximal, but this issue has not been carefully examined. CONCLUSIONS Exercise has definite acute effects on blood lipids, blood pressure, and glucose homeostasis. Exercise also has acute effects on other factors related to atherosclerosis such as immunological function, vascular reactivity, and hemostasis. Considerable additional research is required to define the threshold of exercise required to produce these putatively beneficial effects.

Active commuting to school: How far is too far?

BackgroundWalking and cycling to school provide a convenient opportunity to incorporate physical activity into an adolescents daily routine. School proximity to residential homes has been identified as an important determinant of active commuting among children. The purpose of this study is to identify if distance is a barrier to active commuting among adolescents, and if there is a criterion distance above which adolescents choose not to walk or cycle.MethodsData was collected in 2003–05 from a cross-sectional cohort of 15–17 yr old adolescents in 61 post primary schools in Ireland. Participants self-reported distance, mode of transport to school and barriers to active commuting. Trained researchers took physical measurements of height and weight. The relation between mode of transport, gender and population density was examined. Distance was entered into a bivariate logistic regression model to predict mode choice, controlling for gender, population density socio-economic status and school clusters.ResultsOf the 4013 adolescents who participated (48.1% female, mean age 16.02 ± 0.661), one third walked or cycled to school. A higher proportion of males than females commuted actively (41.0 vs. 33.8%, χ2 (1) = 22.21, p < 0.001, r = -0.074). Adolescents living in more densely populated areas had greater odds of active commuting than those in the most sparsely populated areas (χ2 (df = 3) = 839.64, p < 0.001). In each density category, active commuters travelled shorter distances to school. After controlling for gender and population density, a 1-mile increase in distance decreased the odds of active commuting by 71% (χ2 (df = 1) = 2591.86, p < 0.001). The majority of walkers lived within 1.5 miles and cyclists within 2.5 miles. Over 90% of adolescents who perceived distance as a barrier to active commuting lived further than 2.5 miles from school.ConclusionDistance is an important perceived barrier to active commuting and a predictor of mode choice among adolescents. Distances within 2.5 miles are achievable for adolescent walkers and cyclists. Alternative strategies for increasing physical activity are required for individuals living outside of this criterion.

Exercise intensity‐dependent regulation of peroxisome proliferator‐activated receptor γ coactivator‐1α mRNA abundance is associated with differential activation of upstream signalling kinases in human skeletal muscle

Skeletal muscle contraction increases intracellular ATP turnover, calcium flux, and mechanical stress, initiating signal transduction pathways that modulate peroxisome proliferator‐activated receptor γ coactivator‐1α (PGC‐1α)‐dependent transcriptional programmes. The purpose of this study was to determine if the intensity of exercise regulates PGC‐1α expression in human skeletal muscle, coincident with activation of signalling cascades known to regulate PGC‐1α transcription. Eight sedentary males expended 400 kcal (1674 kj) during a single bout of cycle ergometer exercise on two separate occasions at either 40% (LO) or 80% (HI) of . Skeletal muscle biopsies from the m. vastus lateralis were taken at rest and at +0, +3 and +19 h after exercise. Energy expenditure during exercise was similar between trials, but the high intensity bout was shorter in duration (LO, 69.9 ± 4.0 min; HI, 36.0 ± 2.2 min, P < 0.05) and had a higher rate of glycogen utilization (P < 0.05). PGC‐1α mRNA abundance increased in an intensity‐dependent manner +3 h after exercise (LO, 3.8‐fold; HI, 10.2‐fold, P < 0.05). AMP‐activated protein kinase (AMPK) (2.8‐fold, P < 0.05) and calcium/calmodulin‐dependent protein kinase II (CaMKII) phosphorylation (84%, P < 0.05) increased immediately after HI but not LO. p38 mitogen‐activated protein kinase (MAPK) phosphorylation increased after both trials (∼2.0‐fold, P < 0.05), but phosphorylation of the downstream transcription factor, activating transcription factor‐2 (ATF‐2), increased only after HI (2.4‐fold, P < 0.05). Cyclic‐AMP response element binding protein (CREB) phosphorylation was elevated at +3 h after both trials (∼80%, P < 0.05) and class IIa histone deacetylase (HDAC) phosphorylation increased only after HI (2.0‐fold, P < 0.05). In conclusion, exercise intensity regulates PGC‐1α mRNA abundance in human skeletal muscle in response to a single bout of exercise. This effect is mediated by differential activation of multiple signalling pathways, with ATF‐2 and HDAC phosphorylation proposed as key intensity‐dependent mediators.

BIOTEX—Biosensing Textiles for Personalised Healthcare Management

Textile-based sensors offer an unobtrusive method of continually monitoring physiological parameters during daily activities. Chemical analysis of body fluids, noninvasively, is a novel and exciting area of personalized wearable healthcare systems. BIOTEX was an EU-funded project that aimed to develop textile sensors to measure physiological parameters and the chemical composition of body fluids, with a particular interest in sweat. A wearable sensing system has been developed that integrates a textile-based fluid handling system for sample collection and transport with a number of sensors including sodium, conductivity, and pH sensors. Sensors for sweat rate, ECG, respiration, and blood oxygenation were also developed. For the first time, it has been possible to monitor a number of physiological parameters together with sweat composition in real time. This has been carried out via a network of wearable sensors distributed around the body of a subject user. This has huge implications for the field of sports and human performance and opens a whole new field of research in the clinical setting.

Gender comparison of RPE at absolute and relative physiological criteria.

PURPOSE The effect of gender on ratings of perceived exertion for the overall body (RPE-O), chest (RPE-C), legs (RPE-L), and arms (RPE-A (ski)) was determined. METHODS Comparisons were made at, a) absolute oxygen uptake (VO2, L x min(-1); mL x kg(-1) x min(-1)) and heart rate (HR, b x min(-1)) and b) relative VO2 (%VO2max/peak) and HR (% HRmax/peak) reference criteria. Nine male and 10 female subjects were compared using a perceptual estimation paradigm for treadmill (weight bearing), simulated ski (partial weight bearing), and cycle (nonweight bearing) exercise. RPE was determined by the Borg 15-category scale. RESULTS For each exercise mode, RPE-O, RPE-L, RPE-A (ski), and RPE-C were higher (P < 0.05) in the female than male cohort when compared at submaximal absolute VO2 criteria. RPE did not differ between female and male cohorts when compared at mode specific relative VO2 criteria. Differences in RPE-O, RPE-L, RPE-A (ski), and RPE-C were not found between female and male subjects when comparisons were made at both absolute and relative HR. Responses were consistent for the three exercise modes. CONCLUSION RPE did not differ between gender when comparisons were made at relativized VO2 and HR reference criteria at exercise intensities between 70 and 90% of mode specific maximal/peak values.

A wearable electrochemical sensor for the real-time measurement of sweat sodium concentration

We report a new method for the real-time quantitative analysis of sodium in human sweat, consolidating sweat collection and analysis in a single, integrated, wearable platform. This temporal data opens up new possibilities in the study of human physiology, broadly applicable from assessing high performance athletes to monitoring Cystic Fibrosis (CF) sufferers. Our compact Sodium Sensor Belt (SSB) consists of a sodium selective Ion Selective Electrode (ISE) integrated into a platform that can be interfaced with the human body during exercise. No skin cleaning regime or sweat storage technology is required as the sweat is continually wicked from the skin to a sensing surface and from there to a storage area via a fabric pump. Our results suggest that after an initial equilibration period, a steady-state sodium plateau concentration was reached. Atomic Absorption Spectroscopy (AAS) was used as a reference method, and this has confirmed the accuracy of the new continuous monitoring approach. The steady-state concentrations observed were found to fall within ranges previously found in the literature, which further validates the approach. Daily calibration repeatability (n = 4) was ±3.0% RSD and over a three month period reproducibility was ±12.1% RSD (n = 56). As a further application, we attempted to monitor the sweat of Cystic Fibrosis (CF) sufferers using the same device. We observed high sodium concentrations symptomatic of CF (∼60 mM Na+) for two CF patients, with no conclusive results for the remaining patients due to their limited exercising capability, and high viscosity/low volume of sweat produced.

Effects of preoperative neuromuscular electrical stimulation on quadriceps strength and functional recovery in total knee arthroplasty. A pilot study

BackgroundSupervised preoperative muscle strengthening programmes (prehabilitation) can improve recovery after total joint arthroplasty but are considered resource intensive. Neuromuscular electrical stimulation (NMES) has been shown to improve quadriceps femoris muscle (QFM) strength and clinical function in subjects with knee osteoarthritis (OA) however it has not been previously investigated as a prehabilitation modality.MethodsThis pilot study assessed the compliance of a home-based, NMES prehabilitation programme in patients undergoing total knee arthroplasty (TKA). We evaluated its effect on preoperative and postoperative isometric quadriceps femoris muscle (QFM) strength, QFM cross-sectional area (CSA) and clinical function (subjective and objective). Seventeen subjects were recruited with 14 completing the study (NMES group n = 9; Control group n = 5).ResultsOverall compliance with the programme was excellent (99%). Preoperative QFM strength increased by 28% (p > 0.05) with associated gains in walk, stair-climb and chair-rise times (p < 0.05). Early postoperative strength loss (approximately 50%) was similar in both groups. Only the NMES group demonstrated significant strength (53.3%, p = 0.011) and functional recovery (p < 0.05) from 6 to 12 weeks post-TKA. QFM CSA decreased by 4% in the NMES group compared to a reduction of 12% in the control group (P > 0.05) at 12 weeks postoperatively compared to baseline. There were only limited associations found between objective and subjective functional outcome instruments.ConclusionsThis pilot study has shown that preoperative NMES may improve recovery of quadriceps muscle strength and expedite a return to normal activities in patients undergoing TKA for OA. Recommendations for appropriate outcome instruments in future studies of prehabilitation in TKA have been provided.

Influence of acute exercise with and without carbohydrate replacement on postprandial lipid metabolism

Acute exercise, undertaken on the day before an oral fat tolerance test (OFTT), typically reduces postprandial triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C). However, the benefits of acute exercise may be overstated when studies do not account for compensatory changes in dietary intake. The objective of this study was to determine the influence of acute exercise, with and without carbohydrate (CHO) replacement, on postprandial lipid metabolism. Eight recreationally active young men underwent an OFTT on the morning after three experimental conditions: no exercise [control (Con)], prolonged exercise without CHO replacement (Ex-Def) and prolonged exercise with CHO replacement to restore CHO and energy balance (Ex-Bal). The exercise session in Ex-Def and Ex-Bal consisted of 90 min cycle ergometry at 70% peak oxygen uptake (Vo(2peak)) followed by 10 maximal 1-min sprints. CHO replacement was achieved using glucose solutions consumed at 0, 2, and 4 h postexercise. Muscle glycogen was 40 +/- 4% (P < 0.05) and 94 +/- 3% (P = 0.24) of Con values on the morning of the Ex-Def and Ex-Bal OFTT, respectively. Postprandial TG were 40 +/- 14% lower and postprandial HDL-C, free fatty acids, and 3-hydroxybutyrate were higher in Ex-Def compared with Con (P < 0.05). Most importantly, these exercise effects were not evident in Ex-Bal. Postprandial insulin and glucose and the homeostatic model assessment of insulin resistance (HOMA(IR)) were not significantly different across trials. There was no relation between the changes in postprandial TG and muscle glycogen across trials. In conclusion, the influence of acute exhaustive exercise on postprandial lipid metabolism is largely dependent on the associated CHO and energy deficit.

INTERLEUKIN-15 AND INTERLEUKIN-15Rα SNPs AND ASSOCIATIONS WITH MUSCLE, BONE, AND PREDICTORS OF THE METABOLIC SYNDROME

The aims of this study were to examine associations between two SNPs in the human IL-15 gene and three SNPs in the IL-15Ralpha gene with predictors of metabolic syndrome and phenotypes in muscle, strength, and bone at baseline and in response to resistance training (RT). Subjects were Caucasians who had not performed RT in the previous year and consisted of a strength cohort (n=748), volumetric cohort (n=722), and serum cohort (n=544). Subjects completed 12 weeks of unilateral RT of the non-dominant arm, using their dominant arm as an untrained control. ANCOVA analyses revealed gender-specific associations with: (1) IL-15 SNP (rs1589241) and cholesterol (p=0.04), LDL (p=0.02), the homeostasis model assessment (HOMA; p=0.03), and BMI (p=0.002); (2) IL-15 SNP (rs1057972) and the pre- to post-training absolute difference in 1RM strength (p=0.02), BMI (p=0.008), and fasting glucose (p=0.03); (3) IL-15Ralpha SNP (rs2296135) and baseline total bone volume (p=0.04) and the pre- to post-training absolute difference in isometric strength (p=0.01); and 4) IL-15Ralpha SNP (rs2228059) and serum triglycerides (p=0.04), baseline whole muscle volume (p=0.04), baseline cortical bone volume (p=0.04), and baseline muscle quality (p=0.04). All associations were consistent in showing a potential involvement of the IL-15 pathway with muscle and bone phenotypes and predictors of metabolic syndrome.

Intermodal comparison of energy expenditure at exercise intensities corresponding to the perceptual preference range.

PURPOSE This study compared the rate of energy expenditure among six popular exercise machines at intensities corresponding to ratings of perceived exertion (RPE) for fairly light (RPE-11), somewhat hard (RPE-13), and hard (RPE-15) in 9 healthy men and 10 healthy women. METHODS A maximal exercise test on each exercise machine was used to anchor the Borg 15-point category scale. Subjects performed three submaximal exercise tests at selected RPEs on a treadmill, stair-stepper, cycle ergometer, rowing ergometer, cross-country ski simulator, and rider. The submaximal tests on each exercise device were performed in random order and were 6 min in duration with 15-min rest between trials. Oxygen uptake, heart rate, and blood lactate concentration were measured during the final 2 min of each exercise intensity. RESULTS Energy expenditure at each RPE was highest on the treadmill and ski simulator in men, and on the treadmill, ski simulator, and rowing ergometer in women. Energy expenditure in men and women at all RPEs was lowest on the rider and cycle ergometer. Energy expenditure at a given RPE was greater in men than women on all exercise machines, but men and women used a similar percentage of their machine specific peak oxygen uptake at each RPE on all machines. Heart rate was generally similar among the machines and between both men and women at each RPE. CONCLUSIONS Our results indicated that there are large differences in energy expenditure between exercise machines and between men and women at intensities perceived to be fairly light, somewhat hard, and hard. Consequently, subjects can expend more calories at the same RPE during treadmill and ski simulator exercise, for example, than during exercise with other devices. This may have important implications for the health benefits of different exercises and in promoting long term exercise adherence.