Gary Brickley

Acute hypoxia and exercise improve insulin sensitivity (SI2*) in individuals with type 2 diabetes

Hypoxia has been shown to increase glucose uptake in skeletal muscle using the contraction‐stimulated pathway, independent of the actions of insulin. Yet, the same stress has also been linked with causing insulin resistance and hyperglycaemia. The aim of this study was to examine the effects of acute hypoxia with and without exercise on insulin sensitivity (

Characterising the slope of the distance–time relationship in swimming

S{_{{\rm I}}}^{2*}

Intermittent exercise with and without hypoxia improves insulin sensitivity in individuals with Type 2 diabetes

) in individuals with type 2 diabetes.

The Effect of Hypoxia and Work Intensity on Insulin Resistance in Type 2 Diabetes

The aim of the present study was to assess whether the critical speed calculated by the slope of the distance-time relationship (S(d-t)) represents the boundary between the heavy and severe intensity domains in swimming and would be sustainable during intermittent exercise. Nine competitive male swimmers (mean+/-SD: aged 21.2+/-2.6 yrs; peak (.)VO2 of 3866+/-529 mL min(-1)) performed, (a) four fixed-distance (100-200-400-800 m) all-out efforts to determine S(d-t) and peak (.)VO2; (b) three constant-speed efforts to exhaustion (TTE) at and 5% above and below S(d-t) (S(d-t)(+5%) and S(d-t)(-5%), respectively); (c) a set of 10 x 400 m at S(d-t) with 40-s recovery in between. Capillary blood lactate concentration ([La](B)), oxygen uptake ((.)VO2), and RPE remained stable at S(d-t)(-5%) (TTE=48.9+/-14.1 min) with end values of 3.8+/-1.9 mmol L(-1), 87+/-14% peak (.)VO2, and 4.7+/-1.3. TTE decreased at S(d-t)(+5%) (8.6+/-3.1 min), with end [La](B) of 10.2+/-1.9 mmol L(-1). Peak (.)VO2 was reached at exhaustion. Similarly, S(d-t) could only be maintained for 24.3+/-7.7 min with an increase in RPE and [La](B), (.)VO2 reaching its peak (95+/-5% peak VO2). RPE increased but [La](B) remained stable throughout the ten 400 m blocks performed at S(d-t) (overall time of 53.9+/-2.7 min). The physiological responses when swimming 5% below and 5% above S(d-t) are those characterising the heavy and severe intensity domain, respectively. While S(d-t) lies within the severe intensity domain, intermittent swims at this intensity induce [La](B) steady state alongside high rates of perceived exertion.

Tissue Doppler–Derived Contractile Reserve Is a Simple and Strong Predictor of Cardiopulmonary Exercise Performance across a Range of Cardiac Diseases

CONTEXT Hypoxia and muscle contraction stimulate glucose transport activity in vitro. Exercise and hypoxia have additive effects on insulin sensitivity in type 2 diabetics (T2D). OBJECTIVE The objective of the study was to examine the effectiveness of intermittent exercise with and without hypoxia on acute- and moderate-term glucose kinetics and insulin sensitivity in T2D. SETTING The study was conducted at a university research center. DESIGN, PARTICIPANTS, AND INTERVENTIONS Eight male T2D patients completed the following: 1) 60 min of continuous exercise at 90% lactate threshold in hypoxia (HyEx60); 2) intermittent exercise at 120% lactate threshold, separated by periods of passive recovery (5:5 min) in hypoxia [Hy5:5; O₂ ∼ 14.7 (0.2)%]; and 3) intermittent exercise (5:5 min) at 120% lactate threshold in normoxia (O₂ ∼ 20.93%). MAIN OUTCOME MEASURES Glucose appearance and glucose disappearance, using an adapted non-steady-state one-compartment model were measured. Homeostasis models of insulin resistance (HOMA(IR)), fasting insulin resistance index (FIRI), and β-cell function were calculated 24 and 48 h after exercise conditions. RESULTS Glucose disappearance increased from baseline (1.85 mg/kg · min⁻¹) compared with 24 h (2.01 min/kg · min⁻¹) after HyEx60 (P = 0.031). No difference was noted for both Hy5:5 (P = 0.064) and normoxia (P = 0.385). Hy5:5 demonstrated improvements in HOMA(IR) from baseline [d 1, 6.20 (0.40)] when comparisons were made with d 2 [4.83 (0.41)] (P = 0.0013). HOMA(IR) and FIRI improved in the 24 h (HOMA(IR), P = 0.002; FIRI, P = 0.003), remaining reduced 48 h after HyEx60 (HOMA(IR), P = 0.028; and FIRI, P = 0.034). CONCLUSION HyEx60 offered the greatest improvements in acute and moderate-term glucose control in T2D. Intermittent exercise stimulated glucose disposal and improved post-exercise insulin resistance, which was enhanced when exercise was combined with hypoxia (Hy5:5). The data suggest a use of hypoxic exercise in treatment of T2D.

Limitations to High Intensity Exercise Prescription in Chronic Heart Failure Patients

CONTEXT Hypoxia and muscle contraction stimulate glucose transport in vitro. We have previously demonstrated that exercise and hypoxia have an additive effect on insulin sensitivity in type 2 diabetics. OBJECTIVES Our objective was to examine the effects of three different hypoxic/exercise (Hy Ex) trials on glucose metabolism and insulin resistance in the 48 h after acute hypoxia in type 2 diabetics. DESIGN, PARTICIPANTS, AND INTERVENTIONS Eight male type 2 diabetics completed 60 min of hypoxic [mean (sem) O(2) = ∼14.7 (0.2)%] exercise at 90% of lactate threshold [Hy Ex(60); 49 (1) W]. Patients completed an additional two hypoxic trials of equal work, lasting 40 min [Hy Ex(40); 70 (1) W] and 20 min [Hy Ex(20); 140 (12) W]. MAIN OUTCOME MEASURES Glucose rate of appearance and rate of disappearance were determined using the one-compartment minimal model. Homeostasis models of insulin resistance (HOMA(IR)), fasting insulin resistance index and β-cell function (HOMA(β-cell)) were calculated at 24 and 48 h after trials. RESULTS Peak glucose rate of appearance was highest during Hy Ex(20) [8.89 (0.56) mg/kg · min, P < 0.05]. HOMA(IR) and fasting insulin resistance index were improved in the 24 and 48 h after Hy Ex(60) and Hy Ex(40) (P < 0.05). HOMA(IR) decreased 24 h after Hy Ex(20) (P < 0.05) and returned to baseline values at 48 h. CONCLUSIONS Moderate-intensity exercise in hypoxia (Hy Ex(60) and Hy Ex(40)) stimulates acute- and moderate-term improvements in insulin sensitivity that were less apparent in Hy Ex(20). Results suggest that exercise duration and not total work completed has a greater influence on acute and moderate-term glucose control in type 2 diabetics.

Prognostic importance of tissue velocity imaging during exercise echocardiography in patients with systolic heart failure.

Resting echocardiographic measures of cardiac function such as left ventricular ejection fraction correlate poorly with exercise capacity. Assessment during exercise using measures less dependent on hemodynamic loading conditions, such as tissue Doppler imaging (TDI), may more accurately characterize the relationship between cardiac function and exercise capacity.

A Comparison of High Intensity Interval Training with Circuit Training in a Short-Term Cardiac Rehabilitation Programme for Patients with Chronic Heart Failure

Background: Interval training is recommended for chronic heart failure patients (CHF), but specific guidelines on setting appropriate workloads have not been fully established. The aim of this study was to compare a traditional method of interval training prescription with a protocol specifically designed for CHF. Methods: Ten CHF and 7 healthy controls performed 2 maximal incremental cycle tests to determine interval training workload; a standard test (10 W min−1) and a steep test (25 W.10−s). Peak work rate and oxygen uptake (VO2peak) were determined. Training workloads were defined as 100% standard test and 50% steep test peak work rate. Results: Training workload determined from the standard test was higher than from the steep test in healthy controls (151 ± 17 W vs 118 ± 13 W; P < 0.01), whereas in CHF there was no significant difference between methods (88 ± 10 W vs 96 ± 9 W; P > 0.05). Steep test VO2peak reached 91 ± 5% of standard test VO2peak in controls, and 99 ± 4% in CHF, with no significant differences between tests in either group. Conclusion: Prescribing interval training from a standard test results in higher workloads than from a steep test in healthy individuals, but in CHF both methods prescribe similar workloads. However it should not be assumed that the two tests can be used interchangeably for CHF. This small-sized study raises issues about interval training prescription that may be hypothesis-generating for future larger-scale studies.

An individual approach to monitoring locomotive training load in English Premier League academy soccer players

Resting echocardiography measurements are poor predictors of exercise capacity and symptoms in patients with heart failure (HF). Stress echocardiography may provide additional information and can be expressed using left ventricular ejection fraction (LVEF), or diastolic parameters (E/E′), but LVEF has some major limitations. Systolic annular velocity (S′) provides a measure of longitudinal systolic function, which is relatively easy to obtain and shows a good relationship with exercise capacity. The objective of this study was to investigate the relationship among S′, E/E′ and LVEF obtained during stress echocardiography and both mortality and hospitalisation. A secondary objective was to compare S′ measured using a simplified two-wall model. A total of 80 patients with stable HF underwent exercise stress echocardiography and simultaneous cardiopulmonary exercise testing. Volumetric and tissue velocity imaging (TVI) measurements were obtained, as was peak oxygen uptake (VO2 peak). Of the total number of patients, 11 died and 22 required cardiac hospitalisation. S′ at peak exertion was a powerful predictor for death and hospitalisation. Cut-off points of 5.3 cm/s for death and 5.7 cm/s for hospitalisation provided optimum sensitivity and specificity. This study suggests that, in patients with systolic HF, S′ at peak exertion calculated from the averaged spectral TVI systolic velocity of six myocardial segments, or using a simplified measure of two myocardial segments, is a powerful predictor of future events and stronger than LVEF, diastolic velocities at rest or exercise and VO2 peak. Results indicate that measuring S′ during exercise echocardiography might play an important role in understanding the likelihood of adverse clinical outcomes in patients with HF.

132 The importance of contractile reserve when assessing asymptomatic patients with aortic stenosis

High intensity interval exercise may be a more effective training method than moderate intensity exercise more commonly applied in cardiac rehabilitation. This randomized controlled trial compared the effects of high intensity interval training with moderate intensity circuit training on exercise tolerance and quality of life in patients with chronic heart failure. Twenty six patients with systolic heart failure (left ventricular ejection fraction 15-40%, New York Heart Association class II-III, age 62-87 years) were randomly assigned to circuit training (n=13) or high intensity interval training (n=13) during a 6 week cardiac rehabilitation programme. At baseline and on completion peak oxygen consumption (VO 2peak ), oxygen consumption at ventilatory threshold (VT), ventilatory efficiency and disease specific quality of life were assessed. There was a significant increase in VO 2peak after training in the circuit group only (0.97 ml.kg-1.min-1 P=0.021). Both groups showed significant improvements in VT (circuit 0.55 ml.kg -1.min-1 P=0.050; interval 1.70 ml.kg -1 .min -1 P=0.006) and in quality of life (circuit-7 points P=0.017; interval-5 points P=0.050). There were no significant differences between the two training methods. High intensity interval exercise offers an alternative training mode for improving sub maximal exercise tolerance and quality of life in patients with chronic heart failure. However, the improvements did not match those reported in studies using more frequent and longer duration training interventions.