Gut Microbiota Composition Is Related to Cardiorespiratory Fitness in Healthy Young Adults.

Bacteria residing in the human gastrointestinal tract has a symbiotic relationship with its host. Animal models have demonstrated a relationship between exercise and gut microbiota composition. This was the first study to explore the relationship between cardiorespiratory fitness (maximal oxygen consumption, VO2max) and relative gut microbiota composition (Firmicutes to Bacteroidetes ratio [F/B]) in healthy young adults in a free-living environment. Twenty males and 17 females (25.7 ± 2.2 years), who did not take antibiotics in the last 6 months, volunteered for this study. VO2max was measured using a symptom-limited graded treadmill test. Relative microbiota composition was determined by analyzing DNA extracted from stool samples using a quantitative polymerase chain reaction that specifically measured the quantity of a target gene (16S rRNA) found in Firmicutes and Bacteroidetes. Relationships between F/B and potentially related dietary, anthropometric, and fitness variables were assessed using correlation analyses with an appropriate Bonferroni adjustment (p < .004). The average F/B ratio in all participants was 0.94 ± 0.03. The F/B ratio was significantly correlated to VO2max (r = .48, p < .003), but no other fitness, nutritional intake, or anthropometric variables (p > .004). VO2max explained ∼22% of the variance of an individual's relative gut bacteria as determined by the F/B ratio. These data support animal findings, demonstrating a relationship between relative human gut microbiota composition and cardiorespiratory fitness in healthy young adults. Gastrointestinal bacteria is integral in regulating a myriad of physiological processes, and greater insight regarding ramifications of exercise and nutrition on gut microbial composition may help guide therapies to promote human health.

Metabolic Cost and Exercise Intensity During Active Virtual Reality Gaming.

OBJECTIVE: The aim of this study was to investigate the exercise intensity of active virtual reality games (AVRGs) by oxygen consumption (VO2), heart rate (HR), and rating of perceived exertion (RPE). A second aim was to compare the AVRG intensities to current American College of Sports Medicine exercise guidelines using metabolic equivalents (METs) and %VO2 reserve (%VO2R). MATERIALS & METHODS: HR, VO2, and RPE were collected on participants (N = 41; age: 25.2 ± 4.4 years) during 10-minutes of supine rest and while the participants played each of the following AVRGs for 10 minutes: Thrill of the Fight (TOF), Audioshield (AS), and Holopoint (HP). RESULTS: Compared to resting values of HR (63 ± 10 bpm) and VO2 (4.9 ± 0.6 mL/[kg·min]), there were significant elevations in these variables during TOF (149 ± 16 bpm and 32.5 ± 7.1 mL/[kg·min]), AS (131 ± 24 bpm and 19.1 ± 5.9 mL/[kg·min]), and HP (135 ± 22 bpm and 24.8 ± 6.6 mL/[kg·min]). Based on 95% confidence intervals (CI) of %VO2R, TOF was classified vigorous (68.6% ± 2.8%), HP moderate (49.7% ± 2.7%), and AS light intensity (35.7% ± 2.4%). The 95% CI of METs indicated that TOF was classified vigorous (9.3 ± 0.3 METs), HP moderate to vigorous (7.1 ± 0.3 METs), and AS moderate intensity (5.5 ± 0.3 METs). Lastly, 95% CI of RPE led to TOF being classified as moderate (12.7 ± 0.4), whereas HP (10.5 ± 0.4) and AS (9.3 ± 0.3) were light intensity. CONCLUSIONS: These data suggest that these AVRGs can elicit significant increases in VO2 that are game-dependent, indicating increased energy expenditure. Furthermore, each game had a lower intensity categorization based on RPE compared to %VO2R or METs. These data provide information on the metabolic cost of movement-specific games and may aid consumers and fitness specialists in developing exercise programs with AVRGs.

Dissociation of heart rate variability and heart rate recovery in well-trained athletes.

The purpose of this investigation was to examine the relationships between aerobic fitness, volume of physical activity (PA), heart rate variability (HRV), and heart rate recovery (HRR) in a group of well-trained endurance athletes. Nineteen endurance athletes participated in this study and had aerobic capacities that placed them above the 99th percentile based on normative values (VO(2max): 67.1 ± 2 ml kg(-1) min(-1)). HRV was obtained via an EKG collected during supine rest and reported as high-frequency (HF), low-frequency (LF), and total power (TP). Natural log (ln) transformation was applied when variables violated assumptions of normality. HRR recovery was reported as the reduction in heart rate from peak exercise to the heart rate 1 min after cessation of exercise and PA was estimated from a questionnaire. HRR was significantly correlated with PA and VO(2max) (r = 0.67, P = 0.003 and 0.51, P = 0.039, respectively), but not with any index of HRV. Age was significantly correlated with lnHF (r = -0.49, P = 0.033), lnLF/lnHF (r = 0.48, P = 0.037), and normalized units (NU) of LF (r = 0.47, P = 0.042) and HF (r = -0.47, P = 0.042). Stepwise regression revealed that the strongest predictor of HRR was PA (R (2) = 0.45) and that VO(2max) did not add significant predictive value to the model. The relationship between HRV and age is evident in well-trained endurance athletes, whereas the relationship between HRV and PA/aerobic fitness is not. The maintained relationship between HRR and PA/aerobic fitness suggests that HRR may be a better marker of fitness-related differences in autonomic control in this population.

Accuracy of an infrared LED device to measure heart rate and energy expenditure during rest and exercise.

The purpose of this study was to examine the accuracy of the ePulse Personal Fitness Assistant, a forearm-worn device that provides measures of heart rate and estimates energy expenditure. Forty-six participants engaged in 4-minute periods of standing, 2.0 mph walking, 3.5 mph walking, 4.5 mph jogging, and 6.0 mph running. Heart rate and energy expenditure were simultaneously recorded at 60-second intervals using the ePulse, an electrocardiogram (EKG), and indirect calorimetry. The heart rates obtained from the ePulse were highly correlated (intraclass correlation coefficients [ICCs] ≥0.85) with those from the EKG during all conditions. The typical errors progressively increased with increasing exercise intensity but were <5 bpm only during rest and 2.0 mph. Energy expenditure from the ePulse was poorly correlated with indirect calorimetry (ICCs: 0.01-0.36) and the typical errors for energy expenditure ranged from 0.69-2.97 kcal · min(-1), progressively increasing with exercise intensity. These data suggest that the ePulse Personal Fitness Assistant is a valid device for monitoring heart rate at rest and low-intensity exercise, but becomes less accurate as exercise intensity increases. However, it does not appear to be a valid device to estimate energy expenditure during exercise.

The influence of bar diameter on neuromuscular strength and activation: inferences from an isometric unilateral bench press.

The purpose of this study was to examine the influence of two different bar diameters on neuromuscular activation and strength. The bar diameters used reflected a standard Olympic bar (28 mm (1.1 inch); THIN) and a larger fat bar (51 mm [2 inch]; THICK). Eighteen healthy men (age 25.0 +/- 1 years) were assessed for their maximal voluntary contraction (MVC) during a unilateral isometric bench press exercise with the 2 bar types at 2 different joint angles (angle 1 and angle 2; elbow joint at approximately 45 and 90 degrees , respectively). Additionally, on a separate day, subjects performed three 10-second isometric repetitions at an intensity of 80% MVC using the 2 different bars at angle 1 and angle 2. Electromyographic recordings were collected in the pectoralis major and the muscles of the forearm flexor region at a sampling rate of 1000 Hz during the second day of testing. Analysis of variance was used to examine differences in MVC between bars and also examine between bar differences in electromyographic activity for each muscle group at each joint angle. A significance level of 0.05 was used for all tests. MVC was not different between bar types, although there was a main effect of joint angle on MVC such that it was greater at angle 2. There was a main effect of bar at both angles for the forearm muscles and at angle 1 for the pectoralis such that electromyographic activity was greater with THIN. Our data do not support the hypothesis that bar diameter influences performance during an isometric bench press exercise. However, higher electromyographic activity with THIN suggests greater neuromuscular activation with a standard Olympic bar as opposed to a larger diameter "fat" bar. Although our data do not support the use of a fat bar for increasing neuromuscular activation, these findings should be confirmed in other resistance training exercises.

Cardiac autonomic modulation following high-intensity static muscle contractions.

BACKGROUND: The purpose of this investigation was to examine cardiac autonomic modulation, as measured by wavelet analysis of heart rate variability, following a series of high-intensity static muscle contractions. METHODS: After 10 minutes of rest, electrocardiograms (ECGs) were collected in 17 participants (age, 24.5 +/- 1 yr) 2.5 minutes before (REST) and 10 minutes after a series of static contractions of the knee extensors. Participants performed contractions with the nondominant leg (knee fixed at 90 degrees) at either 70% or 85% (randomized order) of their maximal voluntary contraction (MVC) on two separate visits. The postexercise ECGs were further divided into four consecutive 2.5-minute segments (POST 1-POST 4) to evaluate the time course of any possible autonomic changes after exercise. Each 2.5-minute segment was evaluated for the standard deviation of normal RR intervals (SDNN) and the percentage of successive RR intervals that differed by more than 50 ms (pNN50). Frequency-domain indices were obtained via wavelet transformation giving coefficients that reflected high- and low-frequency fluctuations in heart period (HFw and LFw). RESULTS: SDNN was elevated during POST-1 and pNN50 was reduced during POST-3 and POST-4 (P < 0.05) compared to REST for both intensities. Furthermore, HFw and LFw were increased during POST-1 and reduced during POST-3 and POST-4 compared to REST for both intensities (P < 0.05). CONCLUSION: These data suggest that complex alterations cardiac autonomic modulation exist for at least 10 minutes following a series of high-intensity static contractions performed at either 70% or 85% of MVC.

Heart rate variability after isocaloric exercise bouts of different intensities.

PURPOSE: To examine cardiac autonomic modulation, via heart rate variability (HRV), after exercise bouts at 50% (LO) and 80% (HI) of VO2 reserve (VO2R). METHODS: Thirteen male volunteers (age: 25.7+/-3 yr) exercised on a treadmill at either LO or HI (randomly assigned) on separate days, expending 300 kcal during each bout. During each visit, electrocardiogram (ECG) recordings were obtained during a supine 5-min period before exercise (PRE) and during 30 min of postexercise supine recovery (POST). The last 25 min of POST was divided into five 5-min segments to closely examine postexercise HRV. ECG segments were analyzed for the standard deviation of RR intervals (SDNN), whereas total- (lnTP), low- (lnLF), and high-frequency (lnHF) power were obtained via spectral analysis. LF and HF were further normalized (LFNU and HFNU) to better quantify autonomic balance. RESULTS: There were main effects of time and intensity on SDNN such that it was lower than PRE until 15 min POST, and lower after HI. There were significant intensity x time interactions on lnTP, lnLF, lnHF, LFNU, HFNU, and lnLF/lnHF. Post hoc analysis revealed that lnTP and lnLF were lower than PRE up to 20 min POST after HI. lnHF was lower than PRE for 25 min POST for HI, and for 10 min POST for LO. LFNU and lnLF/lnHF were greater, whereas HFNU was lower, compared with PRE up to 15 min POST, and from 20-25 min POST for HI only. CONCLUSION: Exercise at 50% VO2R caused less of a shift in the cardiac autonomic balance, with a quicker restoration of vagal modulation than exercise at 80% VO2R.

Evidence of an association among age-related changes in physical, psychomotor and autonomic function.

BACKGROUND: autonomic modulation of the heart, as measured by heart rate variability, is directly associated with cardiorespiratory fitness and inversely associated with all-cause mortality. The extent to which cardiorespiratory fitness and heart rate variability are related in older adults is difficult to ascertain due to difficulties in assessing physical fitness among older age groups. OBJECTIVE: to examine heart rate variability and measures of physical function, thereby allowing for the inclusion of a greater cross-section of older adults than can be tested using traditional fitness tests. METHODS: 39 older adults (mean age: 73.2+/-8.1 years; range=60-93 years) underwent evaluation of short-term (5 min) heart rate variability and performance of the American Alliance for Health Physical Education Recreation and Dance Functional Fitness Assessment for Older Adults. Pearson correlation, stepwise multiple regression, and factor analysis were used to describe associations among age, heart rate variability, and functional fitness test-items. RESULTS: significant associations were observed for age and the standard deviation of all normal RR intervals (r=-0.39, P<0.01), and the American Alliance for Health Physical Education Recreation and Dance cardiovascular endurance (r=0.45, P<0.01), strength (r=-0.53, P<0.001), agility (r=0.80, P<0.001), and coordination (r=0.57, P<0.001) items. Standard deviation of all normal RR intervals was negatively associated with the American Alliance for Health Physical Education Recreation and Dance agility (r=-0.37, P<0.01) and coordination (r=-0.49, P<0.001) items. Stepwise multiple regression included only the American Alliance for Health Physical Education Recreation and Dance coordination performance in predicting standard deviation of all normal RR intervals [standard deviation=63.98-2.5 (coordination), F=33.9, P<0.01]. Factor analysis revealed that age, agility, and coordination comprised one factor with a high degree of commonality. CONCLUSION: the association between heart rate variability and coordination suggests concurrent aging of autonomic and psychomotor function.

Influence of short-term endurance exercise training on heart rate variability.

PURPOSE: To examine the influence of 2 wk (eight sessions) of endurance training on cardiac autonomic modulation, as measured by heart rate variability (HRV). METHODS: Twenty-four males (mean age: 23.1 yr) were randomized to an exercise (EX; N = 12) or control group (CT; N = 12). EX trained for eight sessions (4x wk-1, 40 min, 80-85% HRreserve) on a cycle ergometer. ECG tracings were collected during 5 min of paced breathing (12 breaths x min-1 (PB)), 5 min of spontaneous breathing (SB1), 5 min of 70 degrees head-up tilt (TILT), and a second 5-min period of spontaneous breathing (SB2). Data were collected before (test 1), during (tests 2-4), and 48 h after (test 5) the 2-wk period. HRV was reported as the standard deviation of RR intervals, and as natural logarithm of the normalized units (NU) of high- and low-frequency power (lnHF and lnLF). RESULTS: EX exhibited a significant increase in peak oxygen consumption (8%). During PB and TILT conditions, ANOVA revealed a group x time interaction such that EX exhibited lower lnLFNU and lnLF/lnHF during test 5 compared with test 1. CONCLUSION: These data suggest that eight endurance exercise-training sessions performed over 2 wk enhance the relative vagal modulation of the heart during PB and TILT, but not during SB.

Short-term heart rate variability during a cognitive challenge in young and older adults.

BACKGROUND: attention-demanding tasks cause changes in the autonomic modulation of cardiac function. Heart rate variability, an index of autonomic modulation of heart rate, decreases with age. OBJECTIVE: to examine heart rate variability in elderly and young participants at rest and during an attention-demanding task. METHODS: we assessed 16 old participants (ages 72-91) and 16 college-age (ages 20-25) participants for short-term (5 min) heart rate variability at rest and during a simple-reaction time task. We report heart rate variability as the standard deviation of all interbeat intervals, and as the relative contribution of changes occurring at low- and high-frequencies. RESULTS: there were no group differences in resting heart rate. A 2x2 mixed model ANOVA suggested a main effect of age on standard deviation of all interbeat intervals (P<0.05) which was significantly lower for the older group than their younger counterparts. There was also a significant effect of the test condition on standard deviation of all interbeat intervals and spectral measures of heart rate variability (P<0.05) in that standard deviation of all interbeat intervals dropped during the simple reaction time as did high-frequencies, while normalized low frequency power increased. CONCLUSION: cardiac autonomic modulation during provocative stress show similar physiologic responses in young and older adults.