Maximal Workload Capacity Research Articles

The informative power of heart rate along with machine learning regression models to predict maximal oxygen consumption and maximal workload capacity

Prediction of maximal oxygen consumption (VO2max) and maximal workload capacity (MWC) through submaximal exercise tests is an important topic for sports sciences. Numerous studies highlighted the predictive power of submaximal heart rate (HR) and oxygen consumption (VO2) in predicting VO2max and MWC. The challenge is achieving the best possible precision and accuracy by identifying the best predictors and regression models. This project assessed the performance of different indexes along with machine learning regression models to estimate VO2max and MWC. Predictors consisted of biodata (age, weight, and height) along with different combinations of change-scores of HR and VO2 between 0–50 Watts, 50–65 Watts, and 65–80 Watts (Δ0–50, Δ50–65, and Δ65–80, respectively). The use of biodata + HR Δ50–65 + HR Δ65-80 via a Squared Exponential Gaussian Process Regression model resulted in the best performance in predicting VO2max, while the use of biodata + HR Δ0–50 via a Robust Linear Regression model resulted in the best performance in predicting MWC. These results suggest that information provided by HR only during submaximal exercise offers the best predictive mean for estimating VO2max and MWC, while the use of VO2 changes or its addition along with HR changes does not improve predictions. Moreover, different predictors need to be selected for the best estimation of VO2max and MWC. Change-scores refer to absolute value changes, providing information to develop athlete assessment protocols through standardized workloads. These results show practical applicability for sports assessments to be performed indirectly, rapidly, sub-maximally, and through the simple measurement of HR.

Effect Of Co-ingestion Of Carbohydrate With Milk Post-exercise In Women By Menstrual Cycle Phase

PURPOSE: The effect of the post-exercise milk ingestion or co-ingestion of carbohydrate with milk contributes to the recovery of substrate and exercise capacity. However, little information exists on the effect of post-exercise milk consumption on substrate responses and subsequent performance in women. Estrogen, levels of which change with the menstrual cycle, increases fat metabolism. Therefore, one must consider the menstrual cycle when examining the effect of post-exercise milk ingestion in women. Here we aimed to assess the effects of a milk-based beverage on substrate recovery and subsequent exercise performance in women by menstrual cycle phase. METHODS: Twelve women with regular menstrual cycles participated (age, 22.2 ± 2.0 years; height, 1.59 ± 0.55 m; weight, 55.1 ± 6.0 kg; body mass index, 21.7 ± 1.9 kg/m2). The subjects performed glycogen-depleting exercise in the early follicular phase (EF) or late follicular phase (LF), followed by a 240-min recovery period, during which they ingested a carbohydrate beverage (control [CON] group) or carbohydrate dissolved in milk (MILK group). After 240 min, the subjects completed a performance test to exhaustion at 90% maximal workload capacity. Baseline blood samples were taken for the analysis of estradiol and progesterone levels. At t = 0, 120, and 240 min post-exercise, blood samples were taken for the determination of blood glucose, lactate, free fatty acid (FFA), and insulin levels. RESULTS: Serum estradiol levels were significantly higher in the LF (CON and MILK) than in the EF (CON and MILK) (p < 0.01). Serum progesterone levels were not significantly in each group at baseline (p = 0.054). The area under the curve (AUC) of FFA from t = 120 to t = 240 was significantly greater in the MILK (EF and LF) than in the CON (EF and LF) group (12.9 ± 2.3, 13.3 ± 3.6, 18.9 ± 5.5, 18.7 ± 5.6 for the EF + CON, LF + CON, EF + MILK, and LF + MILK, respectively; p < 0.05). There was a significant positive correlation between performance test completion and the AUC of FFA from t = 0 to t = 240 in each group (EF + CON, r = 0.69, p < 0.05; LF + CON, r = 0.59, p < 0.05; EF + MILK, r = 0.83, p < 0.01; LF + MILK, r = 0.65, p < 0.05). CONCLUSION: Our results suggest that circulating substrate and hormone levels during the short post-exercise recovery period may be affected by differences in beverage intake but not the menstrual cycle.

Late‐In‐Life Treadmill‐Training Improves Autophagy, Protein Clearance, and Contractile Function in Mouse Hearts

Evidence exists that a progressive decline of the cellular quality control mechanism called macroautophagy occurs during the process of primary aging. This leads to the accumulation of protein aggregates (i.e., proteotoxicity) that would otherwise be transported to and degraded in the lysosome. Post‐mitotic cells like cardiomyocytes rely heavily on macroautophagy because of their inability to clear defective proteins via cell division. While voluntary wheel running improves cardiac autophagy, lessens cardiac proteotoxicity, and attenuates myocardial dysfunction in mice with desmin‐related cardiomyopathy (Bhuiyan et al., JCI, 2013), the ability for a physiological intervention to improve these indexes in aged mice is unknown. We hypothesized that late‐in‐life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs adult mice. As expected, 24‐month old male C57Bl6 mice (old) exhibited repressed autophagosome formation in the heart, myocardial protein aggregate accumulation, systolic and diastolic dysfunction, and reduced exercise capacity vs. 6‐month old (adult) mice (all p&lt; 0.05; n=10 per group) Separate cohorts of 21 month old mice completed a 10‐week progressive resistance / duration treadmill‐running program (old‐ETR) that improved (all p&lt;0.05): (i) body composition; (ii) maximal workload capacity; and (iii) soleus muscle citrate synthase activity vs. age‐matched sedentary mice (old‐SED). Of note, (iv) mRNA and protein expression of autophagy markers indicated trafficking of the autophagosome to the lysosome increased, (v) protein aggregate clearance improved, and (vi) contractile function was enhanced (all p&lt;0.05), in hearts from old‐ETR vs. old‐SED mice. Dietary maneuvers (e.g., caloric restriction, nutraceutical supplementation) and pharmacological interventions (e.g., rapamycin) are reported to elevate myocardial autophagy and mitigate / reverse age‐associated cardiac dysfunction. Here we show the first evidence that a physiological intervention i.e., late‐in‐life exercise training, improves autophagic flux, protein aggregate clearance, and contractile function in hearts from aged mice.Support or Funding InformationKL [APS STRIDE, UU Undergraduate Research Program (UROP)], JMC (UU Research Fellowship), SKP (AHA 17POST33670663), CR (APS UGRF, UROP), LT (UROP), SB (NIDDK R01‐DK‐098646‐01A1, R01‐DK‐099110, AHA 16GRNT30990018), JDS (AHA16GRNT31050004, NIH RO3AGO52848, NIHRO1HL141540).

Muscle glycogen synthesis and breakdown are both impaired in glycogenin-1 deficiency.

To study fat and carbohydrate metabolism during exercise in patients with glycogenin-1 (GYG1) deficiency, and to study whether IV glucose supplementation can alleviate exercise intolerance in these patients. This is a case-control study with 4 patients with GYG1 deficiency and 4 healthy controls. Patients performed 1 hour of cycling at 50% of their maximal workload capacity, while controls cycled at the same absolute workloads as patients. Heart rate was measured continuously, and production and utilization of fat and glucose was assessed by stable isotope technique. The following day, patients repeated the exercise, this time receiving an IV 10% glucose supplement. Glucose utilization during exercise was similar in patients and controls, while palmitate utilization was greater in patients compared to controls. However, exercise-induced increases in lactate were attenuated to about half normal in patients. This was also the case during a handgrip exercise test. Glucose infusion improved exercise tolerance in patients, and lowered heart rate by on average 11 beats per minute during exercise. The findings suggest that patients with GYG1 deficiency not only have abnormal formation of glycogen, but also have impaired muscle glycogenolysis, as suggested by impaired lactate production during exercise and improved exercise tolerance with glucose infusion.

Exercise Therapy in Type 2 Diabetes

OBJECTIVEGiven the transient nature of exercise-induced improvements in insulin sensitivity, it has been speculated that daily exercise is preferred to maximize the benefits of exercise for glycemic control. The current study investigates the impact of daily exercise versus exercise performed every other day on glycemic control in type 2 diabetic patients.RESEARCH DESIGN AND METHODSThirty type 2 diabetic patients (age 60 ± 1 years, BMI 30.4 ± 0.7 kg/m2, and HbA1c 7.2 ± 0.2%) participated in a randomized crossover experiment. Subjects were studied on three occasions for 3 days under strict dietary standardization but otherwise free-living conditions. Blood glucose homeostasis was assessed by continuous glucose monitoring over 48 h during which subjects performed no exercise (control) or 60 min of cycling exercise (50% maximal workload capacity) distributed either as a single session performed every other day or as 30 min of exercise performed daily.RESULTSThe prevalence of hyperglycemia (blood glucose >10 mmol/L) was reduced from 7:40 ± 1:00 h:min per day (32 ± 4% of the time) to 5:46 ± 0:58 and 5:51 ± 0:47 h:min per day, representing 24 ± 4 and 24 ± 3% of the time, when exercise was performed either daily or every other day, respectively (P < 0.001 for both treatments). No differences were observed between the impact of daily exercise and exercise performed every other day.CONCLUSIONSA short 30-min session of moderate-intensity endurance-type exercise substantially reduces the prevalence of hyperglycemia throughout the subsequent day in type 2 diabetic patients. When total work is being matched, daily exercise does not further improve daily glycemia compared with exercise performed every other day.

Continuous low- to moderate-intensity exercise training is as effective as moderate- to high-intensity exercise training at lowering blood HbA1c in obese type 2 diabetes patients

Aims/hypothesisExercise represents an effective interventional strategy to improve glycaemic control in type 2 diabetes patients. However, the impact of exercise intensity on the benefits of exercise training remains to be established. In the present study, we compared the clinical benefits of 6 months of continuous low- to moderate-intensity exercise training with those of continuous moderate- to high-intensity exercise training, matched for energy expenditure, in obese type 2 diabetes patients.MethodsFifty male obese type 2 diabetes patients (age 59 ± 8 years, BMI 32 ± 4 kg/m2) participated in a 6 month continuous endurance-type exercise training programme. All participants performed three supervised exercise sessions per week, either 55 min at 50% of whole body peak oxygen uptake left( {mathop Vlimits^{ cdot } {text{O}}_{{2{text{peak}}}} } right) (low to moderate intensity) or 40 min at 75% of mathop Vlimits^{ cdot } {text{O}}_{{2{text{peak}}}} (moderate to high intensity). Oral glucose tolerance, blood glycated haemoglobin, lipid profile, body composition, maximal workload capacity, whole body and skeletal muscle oxidative capacity and skeletal muscle fibre type composition were assessed before and after 2 and 6 months of intervention.ResultsThe entire 6 month intervention programme was completed by 37 participants. Continuous endurance-type exercise training reduced blood glycated haemoglobin levels, LDL-cholesterol concentrations, body weight and leg fat mass, and increased mathop Vlimits^{ cdot } {text{O}}_{{2{text{peak}}}} , lean muscle mass and skeletal muscle cytochrome c oxidase and citrate synthase activity (p < 0.05). No differences were observed between the groups training at low to moderate or moderate to high intensity.Conclusions/interpretationWhen matched for energy cost, prolonged continuous low- to moderate-intensity endurance-type exercise training is equally effective as continuous moderate- to high-intensity training in lowering blood glycated haemoglobin and increasing whole body and skeletal muscle oxidative capacity in obese type 2 diabetes patients.Trial registration:ISRCTN32206301Funding:None

Long-standing, insulin-treated type 2 diabetes patients with complications respond well to short-term resistance and interval exercise training

To determine the feasibility and the benefits of combined resistance and interval exercise training on phenotype characteristics and skeletal muscle function in deconditioned, type 2 diabetes (T2D) patients with polyneuropathy. Short-term, single-arm intervention trial. Eleven male T2D patients (age: 59.1+/-7.5 years; body mass index: 32.2+/-4.0 kg/m2) performed progressive resistance and interval exercise training thrice a week for 10 weeks. Besides primary diabetes outcome measures, muscle strength (MUST), maximal workload capacity (Wmax), whole-body peak oxygen uptake (VO2peak) and muscle oxidative capacity (MUOX), intramyocellular lipid (IMCL) and glycogen (IMCG) storage, and systemic inflammation markers were determined before and after training. Daily exogenous insulin requirements (EIR) and historic individualized EIR were gathered and analysed. MUST and Wmax increased with 17% (90% confidence intervals 9-24%) and 14% (6-21) respectively. Furthermore, mean arterial blood pressure declined with 5.5 mmHg (-9.7 to -1.4). EIR dropped with 5.0 IU/d (-11.5 to 1.5) compared with baseline. A decline of respectively -0.7 mmol/l (-2.9 to 1.5) and -147 micromol/l (-296 to 2) in fasting plasma glucose and non-esterified fatty acids concentrations were observed following the intervention, but these were not accompanied by changes in VO2peak, MUOX, IMCL or IMCG, and blood glycolysated haemoglobin, adiponectin, tumor necrosis factor-alpha and/or cholesterol concentrations. Short-term resistance and interval exercise training is feasible in deconditioned T2D patients with polyneuropathy and accompanied by moderate improvements in muscle function and blood pressure. Such a specific exercise regimen may provide a better framework for future exercise intervention programmes in the treatment of deconditioned T2D patients.

Inhibition of adipose tissue lipolysis increases intramuscular lipid use in type 2 diabetic patients

In the present study, we investigated the consequences of adipose tissue lipolytic inhibition on skeletal muscle substrate use in type 2 diabetic patients. We studied ten type 2 diabetic patients under the following conditions: (1) at rest; (2) during 60 min of cycling exercise at 50% of maximal workload capacity and subsequent recovery. Studies were done under normal, fasting conditions (control trial: CON) and following administration of a nicotinic acid analogue (low plasma non-esterified fatty acid trial: LFA). Continuous [U-13C]palmitate and [6,6 -2H2]glucose infusions were applied to quantify plasma NEFA and glucose oxidation rates, and to estimate intramuscular triacylglycerol (IMTG) and glycogen use. Muscle biopsies were collected before and after exercise to determine net changes in lipid and glycogen content specific to muscle fibre type. Following administration of the nicotinic acid analogue (Acipimox), the plasma NEFA rate of appearance was effectively reduced, resulting in lower NEFA concentrations in the LFA trial (p<0.001). Plasma NEFA oxidation rates were substantially reduced at rest, during exercise and subsequent recovery in the LFA trial. The lower plasma NEFA oxidation rates were compensated by an increase in IMTG and endogenous carbohydrate use (p<0.05). Plasma glucose disposal rates did not differ between trials. In accordance with the tracer data, a greater net decline in type I muscle fibre lipid content was observed following exercise in the LFA trial (p<0.05). This study shows that plasma NEFA availability regulates IMTG use, and that adipose tissue lipolytic inhibition, in combination with exercise, could be an effective means of augmenting intramuscular lipid and glycogen use in type 2 diabetic patients in an overnight fasted state.