Function Of Exercise Intensity Research Articles

Recovery Phase Nutrition and Insulin Strategies for a Collegiate Distance Runner with Type 1 Diabetes Mellitus: A Case Study.

There is scant published research regarding nutrition and insulin strategies for athletic performance in collegiate distance runners with type 1 diabetes mellitus (CDRT1). Acute carbohydrate supplementation (CHOsup) and insulin reduction used to minimize hypoglycemia during exercise may result in deteriorated glycemic control post exercise in CDRT1. The present case study of a CDRT1 investigated outcomes associated with a moderate-carbohydrate (ModCHO) diet and 24 h insulin adjustment during recovery phases for improved glycemic control and reduced use of acute strategies. During an 8-day period, a female CDRT1 followed a ModCHO (~4 g/kg/day) nutrition program. Recovery phase adjustments to insulin doses were made using an equation developed to estimate reduced insulin needs post exercise, as a function of exercise intensity and duration. Daily training was performed in the fasted state at 6:00 a.m. and included additional exercise strategies to reduce glycemic variability when needed. Daily blood glucose time-in-range (TIR) and use of CHOsup were assessed. Athlete well-being was determined using the Student-Athlete Well-Being Scale (SAWS)TM at baseline, and days 1, 3, and 7. Throughout the 8-day period, mean TIR increased (77% versus < 50%) and the magnitude of glycemic excursions decreased (~3.8-15 versus ~3.0-26 mmol/L) relative to a prior comparison period. Minimal pre-exercise CHOsup was employed and CHOsup during exercise was not required. Additionally, the athlete achieved a new lifetime best in the 5000 m run and maintained positive well-being. The present case study provides examples of recovery phase strategies (i.e., ModCHO diet and 24 h insulin adjustments) that may support glycemic control and athletic performance in CDRT1 and provides potential considerations for nutrition and insulin strategies for use by athletes and coaches.

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na+/K+-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

Load Carriage and Physical Exertion Influence Soldier Emotional Responses.

Regular aerobic exercise benefits psychological health, enhancing mood in clinical and nonclinical populations. However, single bouts of exercise exert both positive and negative effects on emotion. Exercise reliably increases emotional arousal. Its effects on emotional valence are thought to depend on an interplay between cognitive and interoceptive factors that change as a function of exercise intensity, as studied in clinical, healthy, and athlete populations. However, special populations, such as military, first responders, and endurance athletes, have unique physical exertion requirements that can coincide with additional cognitive, physical, and environmental stressors not typical of the general population. Load carriage is one such activity. The present study examined emotional valence and arousal during sustained, heavy load carriage akin to military training and operations. Thirteen (one woman) active duty soldiers completed a V̇O2max test, a 2-h loaded (up to 50% body mass) and unloaded (empty rucksack) treadmill foot march (3 mph/4% incline) on separate days, during which they rated their exertion and emotional valence and arousal every 40 min. They also completed measures of positive and negative affect and anxiety before and every 20 min after the foot march. Two hours of loaded foot march led to elevated perceived exertion and less positive, more negative and anxious feelings. Higher rated exertion and more negative emotion were associated with higher percent HRmax and V̇O2peak at multiple time points. These results support affect exertion models such as the Dual Mode Theory, whereby physical exertion becomes less pleasant with increasing intensity, and provide insights into how affective responses applied contexts may help predict time to fatigue or failure.

Does sympathetic vasoconstriction contribute to metabolism: Perfusion matching in exercising skeletal muscle?

The process of matching skeletal muscle blood flow to metabolism is complex and multi-factorial. In response to exercise, increases in cardiac output, perfusion pressure and local vasodilation facilitate an intensity-dependent increase in muscle blood flow. Concomitantly, sympathetic nerve activity directed to both exercising and non-active muscles increases as a function of exercise intensity. Several studies have reported the presence of tonic sympathetic vasoconstriction in the vasculature of exercising muscle at the onset of exercise that persists through prolonged exercise bouts, though it is blunted in an exercise-intensity dependent manner (functional sympatholysis). The collective evidence has resulted in the current dogma that vasoactive molecules released from skeletal muscle, the vascular endothelium, and possibly red blood cells produce local vasodilation, while sympathetic vasoconstriction restrains vasodilation to direct blood flow to the most metabolically active muscles/fibers. Vascular smooth muscle is assumed to integrate a host of vasoactive signals resulting in a precise matching of muscle blood flow to metabolism. Unfortunately, a critical review of the available literature reveals that published studies have largely focused on bulk blood flow and existing experimental approaches with limited ability to reveal the matching of perfusion with metabolism, particularly between and within muscles. This paper will review our current understanding of the regulation of sympathetic vasoconstriction in contracting skeletal muscle and highlight areas where further investigation is necessary.

Exercise Duration Affects Session Ratings of Perceived Exertion as a Function of Exercise Intensity.

Session ratings of perceived exertion (sRPE) are considered a practical marker of whole session exercise intensity, but its relationship to exercise volume has remained unclear. We analyzed the effects of exercise duration at different intensities on overall and differentiated sRPE. Sixteen males (Mage = 22.6, SD = 2.2 years; Mheight = 176.4, SD = 5.8 cm; Mweight = 74.0, SD = 5.9 kg; and Mbody fat = 9.4, SD = 2.2%) performed 15 and 30 minute runs at speeds associated with RPE levels of two (weak), three (moderate) and five (strong) on Borg's CR-10 scale during a previous graded exercise test. We used Foster's scale to access sRPE 30 minutes after each trial. Significant increases in sRPE were found with increases in running speed (p < 0.01, ηG2 = 0.48) and duration (p < 0.01, ηG2 = 0.16), with a significant speed X duration interaction (p < 0.01, ηG2 = 0.10). In addition, there was a significant effect for sRPE type (p = 0.01, ηG2 = 0.05) in that overall sRPE was slightly lower than sRPE differentiated to legs and higher than sRPE differentiated to breathing through the trials. Changes in sRPE from 15 to 30-minute trials were minimal for the slow speed and weak sRPE (Cohen´s dz = 0.04 - 0.25) but got higher at the moderate (Cohen´s dz = 0.88 - 1.06) and strong (Cohen´s dz = 1.94 - 2.50) speeds and sRPEs. Thus, exercise duration affects sRPE in an intensity dependent manner. This finding has practical relevance for prescribing exercise, suggesting a need to target specific training loads or aims to optimize trainees' retrospective perceptions of the exercise experience.

Similar rates of fat oxidation during graded submaximal exercise in women of different body composition.

BackgroundModerate intensity exercise ranging 40–60% of maximum oxygen uptake is advised to promote energy expenditure and fat oxidation in overweight and obese people. Although fat oxidation has been shown to be highly variable among individual, there is still a relative uncertainty regarding exercise prescription for women specifically. This article aimed to determine whether indicators of body composition can be used to narrow the exercise intensity range for exercise prescription in women.MethodsA total of 35 healthy women (age 30.8±9.5 yr) classified according to their BMI in normal weight (NOR; ≤24.9 kg·m2), overweight (OVW; 25–29.9 kg·m2) and obese groups (OBE; ≥30 kg·m2) completed a submaximal graded test (intensities eliciting ~30%, 40%, 50% and 60% of maximum oxygen uptake). Blood lactate, perceived exertion and absolute and relative substrate oxidation for fat (OXFAT) and carbohydrates (OXCHO) were measured at each stage.ResultsPerceived exertion and blood lactate increased as a function of exercise but did not differ across groups. There were no significant changes in absolute and relative OXFAT across groups, or as a function of exercise intensity. Peak OXFAT occurred at the 40%, 50% and 40% stages for NOR, OVW and OBE groups, respectively, with no significant differences across groups.ConclusionWe measured no differences, but considerable inter-individual variation, in fat oxidation in women of different body composition. This result is in agreement with previous research based on exercise performed at constant rate and in independent participant groups. Our findings do not support the fat oxidation hypothesis, and further emphasise the perspective that exercise prescription should be individualised and likely be based on considerations other than substrate oxidation.

The relationship between exercise intensity and neurophysiological responses to food stimuli in women: A randomized crossover event-related potential (ERP) study

We tested the effect of different intensities of acute exercise on hunger, and post-exercise energy intake, and neurophysiological measures of attention towards food- and non-food stimuli in women. In a within-subjects crossover design, forty-two women completed no exercise, moderate-intensity exercise, and vigorous-intensity exercise sessions separated by one week, in a counterbalanced fashion. At each session, participants completed a passive viewing task of food (high- and low-calorie) and non-food pictures while electroencephalogram (EEG) data were recorded. The early posterior negativity (EPN), P3, and late positive potential (LPP) components of the event-related potential (ERP) measured neurophysiological responses. Subjective ratings of hunger were measured before and immediately after each condition using a visual analog scale (VAS) and food intake was measured using an ad libitum snack buffet offered at the end of each condition. Results indicated that hunger levels increased as time passed for all sessions. EPN amplitude was larger to non-food compared to food images; P3 amplitude was larger to food than non-food stimuli. LPP amplitude did not differ by high-calorie, low-calorie, or non-food images. Notably, there were no significant main effects or interactions of any ERP component amplitude as a function of exercise intensity. Food intake also did not differ by rest or moderate or vigorous exercise, although subjective arousal ratings to the images were higher after moderate and vigorous exercise compared to rest. Food images also had higher arousal and valence ratings than non-food images overall. Findings indicate that, in this sample, acute moderate and vigorous exercise compared to rest did not disproportionately affect neurophysiological measures of attention to food or non-food stimuli, caloric intake, or hunger.

High adventure shunts old notions of pulmonary vascular control during hypoxic exercise: contrasting views that might just burst your bubble!

High adventure shunts old notions of pulmonary vascular control during hypoxic exercise: contrasting views that might just burst your bubble!

Effects of type of exercise along with caloric restriction on plasma apelin 36 and HOMA-IR in overweight men

Summary Objectives Apelin is an adipokine that is related to regulation of glucose homeostasis and disorders caused by obesity. However, few studies have addressed the effects of exercise in along with caloric restriction on plasma apelin. The purpose of this study was to investigate the impact of different types of exercise along with caloric restriction on plasma apelin 36, TNF-α, and insulin resistance. Material and methods Forty volunteer subjects were randomly divided into four groups: caloric restriction (n = 8) with 500 kcal/d; caloric restriction with high-intensity interval training (n = 10) (6–12 × 1 min intervals running on a treadmill at 90–95% maximal heart rate with 1 min of active rest between the intervals); caloric restriction with continuous training (walking/jogging at 65–70% maximal heart rate) (n = 12); and caloric restriction with resistance training (60–80% one-repetition maximum (1RM)) (n = 10). The protocols were isocaloric. Results Body weight, fat percent, and body mass index (BMI) significantly decreased in all groups (P Conclusion Isocaloric interventions (exercise and nutritional) similarly decreased plasma apelin 36 levels and HOMA-IR in overweight men, whereas plasma levels of TNF-α are a function of exercise intensity.

The Effects of Acute Exercise on Memory and Brain-Derived Neurotrophic Factor (BDNF).

Acute exercise benefits cognition, and some evidence suggests that brain-derived neurotrophic factor (BDNF) plays a role in this effect. The purpose of this study was to explore the dose-response relationship between exercise intensity, memory, and BDNF. Young adults completed 3 exercise sessions at different intensities relative to ventilator threshold (Vt) (VO2max, Vt - 20%, Vt + 20%). For each session, participants exercised for approximately 30 min. Following exercise, they performed the Rey Auditory Verbal Learning Test (RAVLT) to assess short-term memory, learning, and long-term memory recall. Twenty-four hours later, they completed the RAVLT recognition trial, which provided another measure of long-term memory. Blood was drawn before exercise, immediately postexercise, and after the 30-min recall test. Results indicated that long-term memory as assessed after the 24-hr delay differed as a function of exercise intensity with the largest benefits observed following maximal intensity exercise. BDNF data showed a significant increase in response to exercise; however, there were no differences relative to exercise intensity and there were no significant associations between BDNF and memory. Future research is warranted so that we can better understand how to use exercise to benefit cognitive performance.

Selected physiological and perceptual responses during a simulated limited overs century in non-elite batsmen

Few studies have examined the impact of an increased physical demand on batting performance, especially over extended periods of play. Therefore, the purpose of this study was to determine the physiological and perceptual responses of batsmen scoring a simulated limited overs century, and to link these to sprint times and accuracy of the impact of the ball on the bat. Seventeen male, university level cricketers, performed a batting protocol (BATEX©), typical of a limited overs century. The protocol consisted of six stages, each of five overs, with each stage matched to a specific phase of play. Throughout the protocol heart rate (HR), central ratings of perceived effort (RPE), sprint times and impact accuracy were recorded. HR fluctuated as a function of exercise intensity (124.16–159.61 bpm). Central RPE increased as a function of intensity and duration (11.87–16.04). Sprint times got slower over time (5.67–5.81 s), while impact accuracy improved significantly (p < .05) after stage one and then plateaued for the remainder of the protocol (64.81–57.39 mm). In conclusion, the protocol significantly impacted cardiac strain and perceptual responses negatively impacting sprint times with an improvement in batting accuracy.

Correlation Analysis of Exercise-Induced Changes in Plasma Trace Element and Hormone Levels During Incremental Exercise in Well-Trained Athletes.

This study analyzes the relationship between hormonal changes induced by exercise and variations in trace elements associated with oxidative stress during incremental exercise. Nineteen well-trained endurance athletes performed a cycle ergometer test: after a warm-up of 10min at 2.0Wkg(-1), workload increased by 0.5Wkg(-1) every 10min until exhaustion. The analysis was controlled for prior diet and activity patterns, levels of exercise training, and time of day (circadian rhythms). Whole blood lactate concentration and plasma concentrations of ions (Zn, Se, Mn, and Co), insulin, glucagon, aldosterone, thyroid stimulating hormone (TSH), calcitonin, and parathyroid hormone (PTH) were measured at rest; at the end of each stage; and 3, 5, and 7min post-exercise. The statistical analysis involved paired non-parametric tests and correlation coefficients. No significant differences were found in Mn or Co levels as a function of exercise intensity. Zn and Se levels at the end of the exercise protocol and over the recovery time were significantly different to baseline. Further, Zn levels were significantly correlated with aldosterone, calcitonin, and PTH levels, while Se levels were associated with aldosterone, calcitonin, and TSH levels. Our results indicate several different patterns of association between acute changes in hormone concentrations and variations in trace element concentrations related to oxidative stress during submaximal exercise.

Effect of Heat Acclimation on Lactate Excretion Rate and Sodium Ion Reabsorption Rate during Exercise

Sweat production requires two Na+/K+-ATPase energy dependent processes: (i) isoosmotic precursor sweat formation in the secretory coil, and (ii) sodium ion reabsorption along the distal sweat duct. Sweat lactate production has been hypothesized to reflect glycolytic ATP-resynthesis for both processes. Research suggests that heat acclimation does not alter sweat lactate concentration ([Lactate]). This is hard to rationalize considering heat acclimation is reported to increase sweat production and sodium ion reabsorption, which are the energy dependent processes. PURPOSE: (1) To determine the relationships during exercise between sweat rate (SR) and sodium ion reabsorption rate (NaRR), and exercise intensity and lactate excretion rate (LER), and (2) to determine whether heat acclimation affects these relationships. METHODS: Six subjects completed an eight-day heat acclimation protocol comprised of 90-minutes treadmill walking in an environmental chamber set at 39°C and 40% relative humidity. Subjects performed three, 30-minute exercise bouts at 30, 40, and 50% of their previously determined VO2max. Sweat rate was measured volumetrically during each bout on the flexor surface of the proximal half of the forearm. [Lactate] was measured and multiplied by forearm SR to calculate LER. Variables of interest were analyzed using non-parametric Friedman tests. RESULTS: LER, and ratios of LER to NaRR, and [Lactate] to SR were not significantly different between the 30, 40, and 50% workloads or between pre and post-heat acclimation based on 95% confidence intervals. Additionally, these relationships were not significantly different between the three workloads on the first or last day of heat acclimation except for LER to NaRR (p<0.05), which increased from 0.05 ± 0.02 to 0.08 ± 0.02 from 30 to 50% of VO2max. CONCLUSION: These data suggest that sweat gland ATPase activity does not increase as a function of exercise intensity, as demonstrated by LER and NaRR remaining relatively constant. Heat acclimation does not appear to affect these relationships.

The Reliability of a Pain-Based Pacing Strategy during Cycle Ergometry

The intensity of aerobic exercise is typically prescribed as a percent of V†O2 peak and/or heart-rate reserve or VO2 reserve. Perceptions of muscle pain increase as a function of exercise intensity, contribute to perceptions of effort, and may provide an important source of intensity-related information to athletes. In addition, it has been hypothesized that for populations with pathological conditions, such as peripheral vascular disease (PVD), muscle pain is more salient than other perceptions of effort. PURPOSE: To determine the reliability of cycling performance using a pain-based pacing strategy. METHODS: Eleven college-aged males performed 3 bouts of submaximal exercise on a cycle ergometer on separate days. Each bout consisted of a 5 minute warm-up at 50 watts, a 3 minute transition period, and 15 minutes of self-paced exercise. Following the transition period, subjects were instructed to cycle at an intensity that elicited a moderate level of pain in the quadriceps (a “3” on a 0 to 10 pain scale) and to maintain that pain level for the remaining 15-min of the test. Participants were blinded to ergometer power output, but were allowed to freely adjust power output in order to maintain quadriceps pain at a “3”. Distance, power output, V†O2, heart rate, and RPE were recorded every 3 minutes. Reliability was assessed using an intraclass correlation coefficient (ICC) and a repeated-measures ANOVA was used evaluate means among the 3 testing bouts. RESULTS: No significant differences were observed between bouts for any dependent variable (p≥0.05). Distance cycled (0.979), power output (0.946), V†O2 (0.914), heart rate (0.86) and RPE (0.86) all exhibited high day-to-day reliability. CONCLUSIONS: Pain-based pacing leads to reliable exercise performance during cycle ergometry. The use of pain-based pacing in clinical populations such as PVD and those with chronic pain conditions could help the development of more efficacious exercise programs in clinical population who may be limited by pain.

Plasma levels of trace elements and exercise induced stress hormones in well-trained athletes

This study analyzed the variation and relationship of several trace elements, metabolic substrates and stress hormones activated by exercise during incremental exercise. Seventeen well-trained endurance athletes performed a cycle ergometer test: after a warm-up of 10min at 2.0Wkg−1, the workload was increased by 0.5Wkg−1 every 10min until exhaustion. Prior diet, activity patterns, and levels of exercise training were controlled, and tests timed to minimize variations due to the circadian rhythm. Oxygen uptake, blood lactate concentration, plasma ions (Zn, Se, Mn and Co), serum glucose, non-esterified fatty acids (NEFAs) and several hormones were measured at rest, at the end of each stage and 3, 5 and 7min post-exercise. Urine specific gravity was measured before and after the test, and participants drank water ad libitum.Significant differences were found in plasma Zn and Se levels as a function of exercise intensity. Zn was significantly correlated with epinephrine, norepinephrine and cortisol (r=0.884, P<0.01; r=0.871, P<0.01; and r=0.808, P=0.05); and Se showed significant positive correlations whit epinephrine and cortisol (r=0.743, P<0.05; and r=0.776, P<0.05). Neither Zn nor Se levels were associated with insulin or glucagon, and neither Mn nor Co levels were associated with any of the hormones or substrate metabolites studied. Further, while Zn levels were found to be associated only with lactate, plasma Se was significantly correlated with lactate and glucose (respectively for Zn: r=0.891, P<0.01; and for Se: r=0.743, P<0.05; r=0.831, P<0.05).In conclusion, our data suggest that there is a positive correlation between the increases in plasma Zn or Se and stress hormones variations induced by exercise along different submaximal intensities in well-hydrated well-trained endurance athletes.

Determination of respiratory point compensation in healthy adults: Can non-invasive near-infrared spectroscopy help?

We tested the hypothesis that the respiratory compensation point can be accurately determined in healthy participants during incremental cycling exercise using non-invasive near-infrared spectroscopy-derived measures of deoxygenated hemoglobin (deoxyHb). Validation study. 118 healthy men (average age 47 ± 19 yrs, range 20-79 yrs) performed an incremental cycling test to exhaustion. Breath-by-breath pulmonary oxygen uptake (VO2) and other ventilatory and gas exchange variables were measured and used to determine respiratory compensation point. Vastus lateralis deoxyHb was monitored using a frequency domain multi-distance system near-infrared spectroscopy device and deoxyHb data were modeled with a piece-wise double-linear function from which the deoxyHb deflection point (deoxyHbDP) was determined. The absolute (L min(-1)) and relative (% maximal VO2 [VO 2max]) VO2 values associated with the respiratory compensation point and deoxyHbDP were determined for each individual. DeoxyHb increased as a function of exercise intensity up to a point (deoxyHbDP) after which the signal displayed a "near-plateau". The deoxyHbDP corresponded to a VO2 of 2.25 ± 0.69 L min(-1) (74 ± 12% VO 2max) which was not significantly different from the VO2 at respiratory compensation point (2.28 ± 0.70 L min(-1) and 74 ± 10% VO 2max, p < 0.05). Both indices were highly correlated (r(2) = 0.86) and Bland Altman analyses confirmed a non-significant bias for VO2 (-0.024 L min(-1)) concomitant with a small imprecision of 0.26 L min(-1). During incremental cycling exercise, the VO2 associated with the onset of a plateau in near-infrared spectroscopy-derived deoxyHb occurs in coincidence with the VO2 at respiratory compensation point suggesting that respiratory compensation point can be accurately estimated, non-invasively, using near-infrared spectroscopy-derived deoxyHb in alternative to the use of ventilatory-based techniques.

Determination of Maximal Lactate Steady State in Healthy Adults

We tested the hypothesis that the maximal lactate steady state (MLSS) can be accurately determined in healthy subjects based on measures of deoxygenated hemoglobin (deoxyHb), an index of oxygen extraction measured noninvasively by near-infrared spectroscopy (NIRS). Thirty-two healthy men (mean ± SD age = 48 ± 17 yr, range = 23-74 yr) performed an incremental cycling test to exhaustion and square wave tests for MLSS determination. Cardiorespiratory variables were measured bbb and deoxyHb was monitored noninvasively on the right vastus lateralis with a quantitative NIRS device. The individual values of V˙O2 and HR corresponding to the MLSS were calculated and compared to the NIRS-derived MLSS (NIRSMLSS) that was, in turn, determined by double linear function fitting of deoxyHb during the incremental exercise. V˙O2 and HR at MLSS were 2.25 ± 0.54 L·min (76% ± 9% V˙O2max) and 133 ± 14 bpm (81% ± 7% HRmax), respectively. Muscle O2 extraction increased as a function of exercise intensity up to a deflection point, NIRSMLSS, at which V˙O2 and HR were 2.23 ± 0.59 L·min (76% ± 9% V˙O2max) and 136 ± 17 bpm (82% ± 8% HRmax), respectively. For both V˙O2 and HR, the difference of NIRSMLSS from MLSS values was not significant and the measures were highly correlated (r = 0.81 and r = 0.76). The Bland-Altman analysis confirmed a nonsignificant bias for V˙O2 and HR (-0.015 L·min and 3 bpm, respectively) and a small imprecision of 0.26 L·min and 8 bpm. A plateau in muscle O2 extraction was demonstrated in coincidence with MLSS during an incremental cycling exercise, confirming the hypothesis that this functional parameter can be accurately estimated with a quantitative NIRS device. The main advantages of NIRSMLSS over lactate-based techniques are the noninvasiveness and the time/cost efficiency.

Affective change as a function of exercise intensity in a group aerobics class

This study examined, in a naturalistic setting, affective changes in 15 women. Measurements were obtained presession, postsession, and at 10-minute intervals during three aerobics sessions that were conducted at high (HI), low (LI) and self-selected (SS) intensities. The intensity was manipulated via changes in music tempo and movement size. Scores on the Feeling Scale (FS) and the Felt Arousal Scale (FAS) were subjected to two-way repeated measures analysis of variance (ANOVA). Circumplex models were constructed to display the path followed by the affective changes throughout the course of each exercise session. A main effect for time and condition emerged in that the FS scores were more positive in the SS intensity participants than in the LI participants, and the post-test FS scores were more favorable than they were at pretest or at 10 minutes, 20 minutes, 30 minutes, or 40 minutes. The FAS scores were higher in the SS intensity participants and HI participants than in the LI participants. A difference only emerged between the SS intensity and HI participants at the 20-minute interval. Variability in the circumplex profiles was evident across each intensity level and for each participant. The study supports and extends previous work in confirming that: (1) exercise can positively influence affective changes in ecologically valid settings; (2) a self-selected intensity is the most beneficial for producing affective changes; (3) idiosyncratic patterns of affective change occur when exercising at different intensities. The implications of these findings for exercise professionals are discussed.

Lactate kinetics of rainbow trout during graded exercise: Do catheters affect the cost of transport?

Changes in lactate kinetics as a function of exercise intensity have never been measured in an ectotherm. Continuous infusion of a tracer is necessary to quantify rates of lactate appearance (Ra) and disposal (Rd), but it requires double catheterization, which could interfere with swimming. Using rainbow trout, our goals were to: (1) determine the potential effects of catheters and blood sampling on metabolic rate (O2), total cost of transport (TCOT), net cost of transport (NCOT) and critical swimming speed (Ucrit), and (2) monitor changes in lactate fluxes during prolonged, steady-state swimming or graded swimming from rest to Ucrit. This athletic species maintains high baseline lactate fluxes of 24 μmol kg(-1) min(-1) that are only increased at intensities >2.4 body lengths (BL) s(-1) or 85% Ucrit. As the fish reaches Ucrit, Ra is more strongly stimulated (+67% to 40.4 μmol kg(-1) min(-1)) than Rd (+41% to 34.7 μmol kg(-1) min(-1)), causing a fourfold increase in blood lactate concentration. Without this stimulation of Rd during intense swimming, lactate accumulation would double. By contrast, steady-state exercise at 1.7 BL s(-1) increases lactate fluxes to ~30 μmol kg(-1) min(-1), with a trivial mismatch between Ra and Rd that only affects blood concentration minimally. Results also show that the catheterizations and blood sampling needed to measure metabolite kinetics in exercising fish have no significant impact on O2 or TCOT. However, these experimental procedures affect locomotion energetics by increasing NCOT at high speeds and by decreasing Ucrit.

Decline in executive control during acute bouts of exercise as a function of exercise intensity and fitness level

Studies on the effects of acute bouts of cardiovascular exercise on cognitive performances show contradictory findings due to methodological differences (e.g., exercise intensity, cognitive function assessed, participants’ aerobic fitness level, etc.). The present study assessed the acute effect of exercise intensity on cognition while controlling for key methodological confounds. Thirty-seven participants (Mage=23. 8years; SD=2.6) completed a computerized modified-Stroop task (involving denomination, inhibition and switching conditions) while pedalling at 40%, 60% and 80% of their peak power output (PPO). Results showed that in the switching condition of the task, error rates increased as a function of exercise intensity (from 60% to 80% of PPO) in all participants and that lower fit individuals showed increased reaction time variability. This suggests that acute bouts of cardiovascular exercise can momentarily alter executive control and increase performance instability in lower fit individuals.