Increased protein intake derived from leucine-enriched protein enhances the integrated myofibrillar protein synthetic response to short-term resistance training in untrained men and women: a 4-day randomized controlled trial.

Leucine is a critical amino acid stimulating myofibrillar protein synthesis (MyoPS). The consumption of higher leucine-containing drinks stimulates MyoPS, but we know less about higher leucine solid foods. Here, we examined the effect of short-term resistance exercise training (STRT) combined with supplementation of a protein and leucine-enriched bar, compared with STRT alone, on integrated (%/day) rates of MyoPS and anabolic protein signaling. In a nonblinded, randomized crossover trial, eight young adults performed four sessions of STRT without or while consuming the study bar (STRT+Leu, 16 g of protein containing ∼3 g of leucine) for two 4-day phases, separated by 2 days nonexercise (Rest) washout. In combination with serial muscle biopsies, deuterated water permitted the measurement of MyoPS and protein signaling phosphorylation. MyoPS during STRT (1.43 ± 0.06%/day) and STRT+Leu (1.53 ± 0.06%/day) were greater than Rest (1.31 ± 0.05%/day), and MyoPS during STRT+Leu (1.53 ± 0.06%/day) was greater than STRT alone (1.43 ± 0.06%/day). STRT+Leu increased the ratio of phosphorylated to total mechanistic target of rapamycin and 4EBP1 compared to Rest. Engaging in STRT increased integrated MyoPS and protein signaling in young adults and was enhanced with increased protein intake derived from a leucine-enriched protein bar. This study was registered at clinicaltrials.gov as NCT03796897.

Consumption of High-Leucine-Containing Protein Bar Following Breakfast Impacts Aminoacidemia and Subjective Appetite in Older Persons.

BACKGROUND: Limited data are available examining dietary interventions for optimizing protein and leucine intake to stimulate muscle protein synthesis (MPS) in older humans. OBJECTIVES: We aimed to investigate the aminoacidemia and appetite responses of older adults after consuming breakfast, a meal frequently consumed with high-carbohydrate and below-par amounts of protein and leucine for stimulating MPS. METHODS: Five men and 3 women (means ± SD; age: 74 ± 7 y, BMI: 25.7 ± 4.9 kg/m2, fat- and bone-free mass: 63 ± 7 kg) took part in this experiment in which they consumed breakfasts with low-protein (LP = 13 ± 2 g), high-protein (HP = 32 ± 5 g), and LP followed by a protein- and leucine-enriched bar formulation 2 h later (LP + Bar = 29 ± 2 g). The LP, HP, and LP + Bar breakfast conditions contained 519 ± 86 kcal, 535 ± 83 kcal, and 739 ± 86 kcal, respectively. Blood samples were drawn for 6 h and analyzed for amino acid, insulin, and glucose concentrations. Visual analog scales were assessed for hunger, fullness, and desire to eat. RESULTS: The net AUC for essential amino acid (EAA) exposure was similar between the LP + Bar and HP conditions but greater in the HP condition compared with the LP condition. Peak leucinemia was higher in the LP + Bar condition compared with the HP, and both were greater than the LP condition. Net leucine exposure was similar between HP and LP + Bar, and both were greater than LP. Hunger was similarly reduced in LP + Bar and HP, and LP + Bar resulted in a greater hunger reduction than LP. Both LP + Bar and HP resulted in greater net fullness scores than LP. CONCLUSIONS: Consuming our bar formulation increased blood leucine availability and net exposure to EAAs to a similar degree as consuming a high-protein meal. High-protein at breakfast results in a greater net exposure to EAAs and leucine, which could support MPS in older persons. This study was registered at clinicaltrials.gov as NCT03712761.

Novel Essential Amino Acid Supplements Following Resistance Exercise Induce Aminoacidemia and Enhance Anabolic Signaling Irrespective of Age: A Proof-of-Concept Trial.

We investigated the effects of ingesting a leucine-enriched essential amino acid (EAA) gel alone or combined with resistance exercise (RE) versus RE alone (control) on plasma aminoacidemia and intramyocellular anabolic signaling in healthy younger (28 ± 4 years) and older (71 ± 3 years) adults. Blood samples were obtained throughout the three trials, while muscle biopsies were collected in the postabsorptive state and 2 h following RE, following the consumption of two 50 mL EAA gels (40% leucine, 15 g total EAA), and following RE with EAA (combination (COM)). Protein content and the phosphorylation status of key anabolic signaling proteins were determined via immunoblotting. Irrespective of age, during EAA and COM peak leucinemia (younger: 454 ± 32 µM and 537 ± 111 µM; older: 417 ± 99 µM and 553 ± 136 µM) occurred ~60-120 min post-ingestion (younger: 66 ± 6 min and 120 ± 60 min; older: 90 ± 13 min and 78 ± 12 min). In the pooled sample, the area under the curve for plasma leucine and the sum of branched-chain amino acids was significantly greater in EAA and COM compared with RE. For intramyocellular signaling, significant main effects were found for condition (mTOR (Ser2481), rpS6 (Ser235/236)) and age (S6K1 (Thr421/Ser424), 4E-BP1 (Thr37/46)) in age group analyses. The phosphorylation of rpS6 was of similar magnitude (~8-fold) in pooled and age group data 2 h following COM. Our findings suggest that a gel-based, leucine-enriched EAA supplement is associated with aminoacidemia and a muscle anabolic signaling response, thus representing an effective means of stimulating muscle protein anabolism in younger and older adults following EAA and COM.

Aminoacidemia following ingestion of native whey protein, micellar casein, and a whey-casein blend in young men.

We examined the aminoacidemic, glycemic, and insulinemic responses following ingestion of 25 g of native whey protein, micellar casein, and a 1:1 blend of whey and casein in randomized order in young adult men. Blood samples were drawn at baseline and at regular intervals for 6 h following ingestion. Area under curve and peak plasma essential amino acid concentrations after the ingestion of the protein blend were similar to whey and greater compared with casein.

Perspective: Protein Requirements and Optimal Intakes in Aging: Are We Ready to Recommend More Than the Recommended Daily Allowance?

The Dietary Reference Intakes set the protein RDA for persons >19 y of age at 0.8 g protein ⋅ kg body weight-1 ⋅ d-1. A growing body of evidence suggests, however, that the protein RDA may be inadequate for older individuals. The evidence for recommending a protein intake greater than the RDA comes from a variety of metabolic approaches. Methodologies centered on skeletal muscle are of paramount importance given the age-related decline in skeletal muscle mass and function (sarcopenia) and the degree to which dietary protein could mitigate these declines. In addition to evidence from short-term experimental trials, observational data show that higher protein intakes are associated with greater muscle mass and, more importantly, better muscle function with aging. We are in dire need of more evidence from longer-term intervention trials showing the efficacy of protein intakes that are higher than the RDA in older persons to support skeletal muscle health. We propose that it should be recommended that older individuals consume ≥1.2 g protein · kg-1 · d-1 and that there should be an emphasis on the intake of the amino acid leucine, which plays a central role in stimulating skeletal muscle anabolism. Critically, the often-cited potential negative effects of consuming higher protein intakes on renal and bone health are without a scientific foundation in humans.

Defining anabolic resistance: implications for delivery of clinical care nutrition.

PURPOSE OF REVIEW: Skeletal muscle mass with aging, during critical care, and following critical care is a determinant of quality of life and survival. In this review, we discuss the mechanisms that underpin skeletal muscle atrophy and recommendations to offset skeletal muscle atrophy with aging and during, as well as following, critical care. RECENT FINDINGS: Anabolic resistance is responsible, in part, for skeletal muscle atrophy with aging, muscle disuse, and during disease states. Anabolic resistance describes the reduced stimulation of muscle protein synthesis to a given dose of protein/amino acids and contributes to declines in skeletal muscle mass. Physical inactivity induces: anabolic resistance (that is likely exacerbated with aging), insulin resistance, systemic inflammation, decreased satellite cell content, and decreased capillary density. Critical illness results in rapid skeletal muscle atrophy that is a result of both anabolic resistance and enhanced skeletal muscle breakdown. SUMMARY: Insofar as atrophic loss of skeletal muscle mass is concerned, anabolic resistance is a principal determinant of age-induced losses and appears to be a contributor to critical illness-induced skeletal muscle atrophy. Older individuals should perform exercise using both heavy and light loads three times per week, ingest at least 1.2 g of protein/kg/day, evenly distribute their meals into protein boluses of 0.40 g/kg, and consume protein within 2 h of retiring for sleep. During critical care, early, frequent, and multimodal physical therapies in combination with early, enteral, hypocaloric energy (∼10-15 kcal/kg/day), and high-protein (>1.2 g/kg/day) provision is recommended.

Dissociations among direct and indirect indicators of adiposity in young wrestlers.

The purposes of this study were to: (a) examine the age-related patterns of differences in height (HT), body mass (BM), percent body fat (% fat), body mass index (BMI), and skinfolds (SF) in 11- to 18-year-old wrestlers; (b) determine the coherence of direct (% fat) and indirect (BMI and SFs) indicators of adiposity in the wrestlers; and (c) compare the age-related patterns and mean values for HT, BM, BMI, subscapular, and triceps SF for the wrestlers to those of national samples of boys from the National Health and Nutrition Examination Survey (NHANES) database. One hundred thirty wrestlers were divided into 8 independent yearly age groups (AG): AG11-AG18 years. Height, BM, BMI, subscapular SF, triceps SF, medial calf SF, thigh SF, sum of SFs, and % fat were assessed. There were no differences between the wrestlers and NHANES samples for age-related patterns of BMI (0.61 and 0.63 kg·m·y), subscapular SF (0.47 and 0.37 mm·y), or triceps SF (-0.31 and -0.39 mm·y). Furthermore, the wrestlers displayed no differences in % fat between age groups. The results indicated that: (a) dissociations existed between the direct and indirect indicators of adiposity; (b) the wrestlers were similar in height but had smaller upper-body SFs when compared with NHANES samples; and (c) participation in wrestling (1-8 years) had no adverse effects on the normal age-related growth patterns for HT, but favorable effects on measures of adiposity.

Differences among estimates of critical power and anaerobic work capacity derived from five mathematical models and the three-minute all-out test.

Estimates of critical power (CP) and anaerobic work capacity (AWC) from the power output vs. time relationship have been derived from various mathematical models. The purpose of this study was to examine estimates of CP and AWC from the multiple work bout, 2- and 3-parameter models, and those from the 3-minute all-out CP (CP3min) test. Nine college-aged subjects performed a maximal incremental test to determine the peak oxygen consumption rate and the gas exchange threshold. On separate days, each subject completed 4 randomly ordered constant power output rides to exhaustion to estimate CP and AWC from 5 regression models (2 linear, 2 nonlinear, and 1 exponential). During the final visit, CP and AWC were estimated from the CP3min test. The nonlinear 3-parameter (Nonlinear-3) model produced the lowest estimate of CP. The exponential (EXP) model and the CP3min test were not statistically different and produced the highest estimates of CP. Critical power estimated from the Nonlinear-3 model was 14% less than those from the EXP model and the CP3min test and 4-6% less than those from the linear models. Furthermore, the Nonlinear-3 and nonlinear 2-parameter (Nonlinear-2) models produced significantly greater estimates of AWC than did the linear models and CP3min. The current findings suggested that the Nonlinear-3 model may provide estimates of CP and AWC that more accurately reflect the asymptote of the power output vs. time relationship, the demarcation of the heavy and severe exercise intensity domains, and anaerobic capabilities than will the linear models and CP3min test.

Metabolic, cardiovascular, and perceptual responses to a thermogenic nutritional supplement at rest, during exercise, and recovery in men.

Twenty-one men (mean ± SD; age = 23.5 ± 2.6 years, BMI = 26.0 ± 2.4 kg-1·m-2) completed this randomized, double-blinded, placebo-controlled, crossover study to examine acute responses to a thermogenic nutritional supplement. Each testing session included: (a) 30 minutes resting, followed by placebo or thermogenic nutritional supplementation, (b) 50 minutes postsupplementation resting, (c) 60 minutes walking, and (d) 50 minutes postexercise recovery. Gas exchange variables and heart rate (HR) were recorded during each phase. Blood pressure was recorded during all phases except exercise. Ratings of perceived exertion (RPE) were recorded only during exercise. There were no significant differences for any of the measures between the supplement and placebo during the initial resting or postsupplementation phases. During exercise, energy expenditure (EE) (placebo = 18.98-19.06 kJ·min-1 and supplement = 19.44-19.82 kJ·min-1) and VO2 (placebo = 11.27-11.35 ml·kg-1·min-1; supplement = 11.64-11.82 ml·kg-1·min-1) were greater for the supplement than placebo. There were no differences in respiratory exchange ratio (RER), HR, or RPE between the supplement and placebo during exercise. Postexercise, only VO2 (placebo = 3.53-3.63 ml·kg-1·min-1; supplement = 3.71-3.84 ml·kg-1·min-1) was greater for the supplement than placebo, but there were no differences in EE, RER, HR, or blood pressure. These findings suggested that the specific blend of ingredients in the thermogenic nutritional supplement, when combined with exercise, increased the metabolic rate with minimal changes in cardiovascular function and no effect on RPE.

Effects of anatabine and unilateral maximal eccentric isokinetic muscle actions on serum markers of muscle damage and inflammation.

The purpose of this study was to examine the effects of anatabine supplementation in conjunction with unilateral, maximal eccentric isokinetic muscle actions on serum markers of muscle damage and pro-inflammatory cytokines in humans. Seventeen men (mean ± S.D. age = 22.4 ± 3.2 yrs) participated in this double-blinded, placebo-controlled, crossover study. Participants were randomly assigned to two 10-day conditions (anatabine and placebo) separated by a 2-4 week washout period. After seven days of supplementation, blood was sampled immediately prior to PRE, immediately following POST, and 24, 48, and 72 h after 6 sets of 10 repetitions of unilateral, maximal eccentric isokinetic forearm flexion exercise. Concentrations of serum creatine kinase, lactate dehydrogenase, myoglobin, high sensitivity c-reactive protein, and TNF-α were measured. Creatine kinase, myoglobin, and lactate dehydrogenase increased (P<0.05), while high sensitivity c-reactive protein and TNF-α did not change (P>0.05) after the eccentric exercise during both conditions. Lactate dehydrogenase was higher (P<0.05) during the anatabine condition. The primary findings of this study were two-fold: (a) anatabine had no beneficial effects on traditional markers of muscle damage (creatine kinase, lactate dehydrogenase, and myoglobin) compared to placebo after the eccentric exercise protocol, and (b) the eccentric exercise protocol did not elicit increase in the pro-inflammatory cytokines (c-reactive protein and TNF-α). Future studies are needed to examine the effects of anatabine on naturally-occurring inflammation that is common with aging or obesity. Furthermore, additional research is needed to examine the relationship between muscle damage and inflammation after eccentric exercises of different modes, durations, and intensities.

The effects of polyethylene glycosylated creatine supplementation on anaerobic performance measures and body composition.

The purpose of this study was to examine the effects of 28 days of polyethylene glycosylated creatine (PEG-creatine) supplementation (1.25 and 2.50 g·d) on anaerobic performance measures (vertical and broad jumps, 40-yard dash, 20-yard shuttle run, and 3-cone drill), upper- and lower-body muscular strength and endurance (bench press and leg extension), and body composition. This study used a randomized, double-blind, placebo-controlled parallel design. Seventy-seven adult men (mean age ± SD, 22.1 ± 2.5 years; body mass, 81.7 ± 10.8 kg) volunteered to participate and were randomly assigned to a placebo (n = 23), 1.25 g·d of PEG-creatine (n = 27), or 2.50 g·d of PEG-creatine (n = 27) group. The subjects performed anaerobic performance measures, muscular strength (one-repetition maximum [1RM]), and endurance (80% 1RM) tests for bench press and leg extension, and underwater weighing for the determination of body composition at day 0 (baseline), day 14, and day 28. The results indicated that there were improvements (p < 0.0167) in vertical jump, 20-yard shuttle run, 3-cone drill, muscular endurance for bench press, and body mass for at least one of the PEG-creatine groups without changes for the placebo group. Thus, the present results demonstrated that PEG-creatine supplementation at 1.25 or 2.50 g·d had an ergogenic effect on lower-body vertical power, agility, change-of-direction ability, upper-body muscular endurance, and body mass.

An examination of neuromuscular and metabolic fatigue thresholds.

This study examined the relationships among the physical working capacity at the fatigue threshold (PWCFT), the power outputs associated with the gas exchange threshold (PGET) and the respiratory compensation point (PRCP), and critical power (CP) to identify possible physiological mechanisms underlying the onset of neuromuscular fatigue. Ten participants (mean ± SD age: 20 ± 1 years) performed a maximal incremental cycle ergometer test to determine the PWCFT, PGET, and PRCP. CP was determined from the 3 min all-out test. The PWCFT (197 ± 55 W), PRCP (212 ± 50 W), and CP (208 ± 63 W) were significantly greater than the PGET (168 ± 40 W), but there were no significant differences among the PWCFT, PRCP, and CP. All thresholds were significantly inter-4 (r = 0.794-0.958). The 17% greater estimates for the PWCFT than PGET were likely related to differences in the physiological mechanisms that underlie these fatigue thresholds, while the non-significant difference and high correlation between the PWCFT and the PRCP suggested that hyperkalemia may underlie both thresholds. Furthermore, it is possible that the 5% lower estimate of the PWCFT than CP could more accurately reflect the demarcation of the heavy from severe exercise intensity domains.

Physiologic responses to a thermogenic nutritional supplement at rest, during low-intensity exercise, and during recovery from exercise in college-aged women.

This study examined acute physiologic responses to a thermogenic nutritional supplement at rest, during exercise, and during recovery from exercise in women. Twelve women (mean ± SD age, 22.9 ± 3.1 years) were recruited for this randomized, double-blinded, placebo-controlled, crossover study. Each testing session consisted of 4 phases: 30 min of presupplementation resting, followed by the ingestion of the placebo or thermogenic nutritional supplement; 50 min of postsupplementation resting; 60 min of walking (at 3.2-4.8 km·h(-1)); and 50 min of postexercise resting. Energy expenditure (EE), oxygen consumption, respiratory exchange ratio (RER), oxygen (O2) pulse, and heart rate (HR) values were recorded during all 4 phases. Systolic (SBP) and diastolic (DBP) blood pressure were recorded during the rest, postsupplementation, and postexercise recovery phases; ratings of perceived exertion (RPE) were recorded only during exercise. There were no significant differences for EE, oxygen consumption, O2 pulse, HR, SBP, or DBP between the supplement and placebo during the presupplementation resting or postsupplementation phases. The RER, however, was higher with the supplement at 30 min postsupplementation. During exercise, EE and O2 pulse were 3%-6% greater with the supplement than placebo; there were no significant differences in RPE. Postexercise, EE, oxygen consumption, and DBP were 3%-7% greater with the supplement than placebo. These findings suggest that a thermogenic nutritional supplement, when combined with exercise, increases metabolic rate but has no effect on the perception of effort and results in only minimal changes in cardiovascular function.

The relationships among critical power determined from a 3-min all-out test, respiratory compensation point, gas exchange threshold, and ventilatory threshold.

PURPOSE: Critical power (CP) from the 3-min test was compared to the power outputs associated with thresholds determined from gas exchange parameters that have been used to demarcate the exercise-intensity domains including the respiratory compensation point (RCP), gas exchange threshold (GET), and ventilatory threshold (VT). METHOD: Twenty-eight participants performed an incremental-cycle ergometer test to exhaustion. The VT was determined from the relationship between the ventilatory equivalent for oxygen uptake (VE/VO2) versus VO2 and the GET was determined using the V-slope method (VCO2 vs. VO2). The RCP was identified from the VE-versus-VCO2 relationship. CP was the average power output during the last 30 s of the 3-min all-out test. Linear regression was used to determine the power outputs associated with the RCP, GET, and VT, as well as the VO2 associated with CP. Mean differences among the associated power outputs, percent VO2 peak, and percent peak power output for the GET, VT, RCP, and CP were analyzed using separate one-way repeated-measures analyses of variance. RESULTS: There were no significant differences between CP (187 +/- 47W) and the power output associated with RCP (190 +/- 49W) or between the power outputs associated with GET (139 +/- 37W) and VT (145 +/- 37W). The power outputs associated with GET and VT, however, were significantly less than were those at CP and associated with RCRP. CONCLUSIONS: These findings suggest CP and RCP demarcate the heavy from severe exercise-intensity domain and result from a different mechanism of fatigue than that of GET and VT, possibly hyperkalemia.

The effects of anatabine on non-invasive indicators of muscle damage: a randomized, double-blind, placebo-controlled, crossover study.

BACKGROUND: Anatabine (ANA), a minor tobacco alkaloid found in the Solanaceae family of plants, may exhibit anti-inflammatory activity, which may be useful to aid in recovery from exercise-induced muscle damage. The purpose of this study, therefore, was to examine the effects of ANA supplementation on the recovery of isometric strength and selected non-invasive indicators of muscle damage. METHODS: A double-blinded, placebo-controlled, crossover design was used to study eighteen men (mean ± SD age = 22.2 ± 3.1 yrs; body mass = 80.3 ± 15.7 kg) who participated in two randomly-ordered conditions separated by a washout period. The ANA condition consisted of consuming 6-12 mg anatabine per day for 10 days, while testing took place during days 7-10. The placebo (PLA) condition was identical except that the PLA supplement contained no ANA. Maximal voluntary isometric peak torque (PT) of the forearm flexors, arm circumference, hanging joint angle, and subjective pain ratings were measured before (PRE), immediately after (POST), and 24, 48, and 72 h after six sets of 10 maximal, eccentric isokinetic forearm flexion muscle actions. Resting heart rate and blood pressure were measured at PRE and 72 h in each condition. RESULTS: For PT, hanging joint angle, arm circumference, and subjective pain ratings, there were no condition x time (p > 0.05) interactions, there were no main effects for condition (p > 0.05), but there were main effects for time (p < 0.001). There were no condition x time (p > 0.05) interactions and no main effects for condition (p > 0.05) or time (p > 0.05) for blood pressure or resting heart rate. CONCLUSIONS: ANA supplementation had no effect on the recovery of muscle strength, hanging joint angle, arm swelling, or subjective pain ratings after a bout of maximal eccentric exercise in the forearm flexors. Therefore, ANA may not be beneficial for those seeking to improve recovery from heavy eccentric exercise. Future studies should examine the effects of ANA on the pro-inflammatory cytokine responses to exercise-induced muscle damage and the chronic low-grade inflammation observed in obese and elderly individuals.

Neuromuscular and metabolic comparisons between ramp and step incremental cycle ergometer tests.

INTRODUCTION: We compared peak and submaximal mean values for neuromuscular and metabolic parameters between ramp (15 W · min(-1)) and step (30 W increments every 2 min) incremental cycle ergometer tests. METHODS: Thirteen healthy adults (7 men and 6 women; mean ± SD age = 23.4 ± 3.3 years) performed randomly ordered ramp or step incremental tests. Two-way repeated measures analyses of variance were used to analyze the data. RESULTS: The ramp incremental test resulted in lower mean EMG amplitude, O2, and HR values at the common power outputs, with no differences for MMG amplitude values. CONCLUSIONS: It is possible that the cumulative effect of producing an increased amount of work during the step (total work = 75.83 kJ) vs. ramp (total work = 65.60 kJ) incremental cycle ergometer tests at the common power outputs may have contributed to the greater fatigue-induced increase in muscle recruitment and/or firing rate, oxygen consumption, and heart rate.

Metabolic and neuromuscular responses at critical power from the 3-min all-out test.

The purpose of this study was to determine the specific metabolic and neuromuscular responses at critical power (CP) from the 3-min all-out test. Nine men (mean ± SD: aged 23.7 ± 3.3 years) performed an incremental test for the determination of peak oxygen consumption (VO(2peak)) and gas exchange threshold. CP was estimated for each subject from the 3-min all-out test. Oxygen consumption (VO(2)), the ventilation versus carbon dioxide production ratio (V(E)/VCO(2) ratio), electromyographic (EMG) amplitude, and EMG mean power frequency (MPF) were examined during exhaustive rides at CP for each subject. There was no significant difference between the VO(2) at exhaustion (40.6 ± 7.5 mL·kg(-1)·min(-1)) and VO(2peak) (42.9 ± 7.3 mL·kg(-1)·min(-1)). Furthermore, there were significant increases in EMG amplitude and the V(E)/VCO(2) ratio during the exhaustive rides at CP. There was, however, no significant change in EMG MPF over time. Therefore, the current findings indicated that the 3-min all-out test overestimated CP and the demarcation between the heavy- and severe-intensity domains. Specifically, the VO(2), ventilatory, and EMG amplitude responses were consistent with those observed during continuous exercise in the severe exercise intensity domain. It is likely that the ventilatory and EMG amplitude responses were associated with a common mechanism of fatigue that is different from what affects EMG MPF.

Responses during exhaustive exercise at critical power determined from the 3-min all-out test.

The purpose of the present study was to examine oxygen consumption rate ([Vdot][Formula: see text]), heart rate (HR), and ratings of perceived exertion (RPE) responses, as well as time to exhaustion (Tlim) values during continuous rides at critical power (CP) determined from the 3-min all-out test. Eighteen participants (mean ± s: 23.6 ± 3.5 years; 72.7 ± 18.2 kg) performed an incremental cycle ergometer test to exhaustion to determine peak oxygen consumption rate ([Vdot][Formula: see text] peak) and HR peak. Critical power was determined from the 3-min all-out test. Metabolic responses ([Vdot][Formula: see text] and heart rate), RPE, and Tlim were recorded during continuous rides to exhaustion at CP. Linear regression and t-tests were used to compare [Vdot][Formula: see text], heart rate, and RPE responses during the continuous rides to exhaustion. The Tlim at CP was 12.5 ± 6.5 min. There were significant increases in [Vdot][Formula: see text], HR, and RPE during the continuous rides at CP and 15 of the 18 participants reached [Vdot][Formula: see text] peak at exhaustion. Therefore, the [Vdot][Formula: see text], heart rate, and RPE responses, as well as the Tlim values in the present study suggested that CP determined from the 3-min all-out test overestimated the "true" CP and was within the severe exercise intensity domain.

Electromyographic and mechanomyographic responses across repeated maximal isometric and concentric muscle actions of the leg extensors.

The purpose of the present study was to examine the patterns of responses for torque, electromyographic (EMG) amplitude, EMG mean power frequency (MPF), mechanomyographic (MMG) amplitude, and MMG MPF across 30 repeated maximal isometric (ISO) and concentric (CON) muscle actions of the leg extensors. Twelve female subjects (21.1±1.4yrs; 63.3±7.4kg) performed ISO and CON fatigue protocols with EMG and MMG signals recorded from the vastus lateralis. The relationships for torque, EMG amplitude, EMG MPF, MMG amplitude, and MMG MPF versus repetition number were examined using polynomial regression. The results indicated there were decreases (p<0.05) across the ISO muscle actions for torque (r(2)=0.95), EMG amplitude (R(2)=0.44), EMG MPF (r(2)=0.62), and MMG MPF (r(2)=0.48), but no change in MMG amplitude (r(2)=0.07). In addition, there were decreases across the CON muscle actions for torque (R(2)=0.97), EMG amplitude (R(2)=0.46), EMG MPF (R(2)=0.86), MMG amplitude (R(2)=0.44), and MMG MPF (R(2)=0.80). Thus, the current findings suggested that the mechanisms of fatigue and motor control strategies used to modulate torque production were similar between maximal ISO and CON muscle actions.

Mechanomyographic and metabolic responses during continuous cycle ergometry at critical power from the 3-min all-out test.

There are limited data regarding metabolic responses during continuous exhaustive rides at critical power (CP) from the 3-min all-out test. In addition, no previous studies have examined the mechanomyographic (MMG) responses at CP from the 3-min all-out test. Therefore, this study examined the metabolic and MMG responses during continuous exercise at CP determined from the 3-min all-out test. Nine college-aged females (mean±SD: age 23.0±3.6yrs) performed an incremental test to exhaustion on a cycle ergometer to identify the gas exchange threshold, peak oxygen consumption rate (V˙O2 peak) and heart rate peak (HR peak). The V˙O2, HR, MMG amplitude and mean power frequency (MPF) responses were examined during continuous rides to exhaustion at CP (81±6% peak power). There were significant increases in V˙O2 and HR over time and there was no significant difference between V˙O2 peak and V˙O2 at exhaustion or HR peak and HR at exhaustion. There were, however, no significant changes for MMG amplitude or MPF over time. Therefore, the current findings suggested that the 3-min all-out test overestimated CP and the demarcation between the heavy and severe intensity domains. Specifically, the V˙O2 and HR responses did not reach a steady state and were driven to peak values. Furthermore, the non-significant change in MMG amplitude and MPF were consistent with the responses observed at fatiguing power outputs (i.e., >80% peak power).