Authenticity of the Ratio of Inorganic Phosphate to Phosphocreatine as a Marker for Respiratory Stress During a Maximal Aerobic Exercise

Under the context of assessing the effects of mitochondrial stress on skeletal muscles, consideration for the ratio of inorganic phosphate to phosphocreatine (Pi:PCr) may be used as a surrogate marker. Furthermore, assessing the systemic Pi:PCr, under states of high metabolic and respiratory demands with reduced oxygen supply (VO2), such as strenuous exercise while only using nasal breathing (NB), might provide valuable information regarding respiratory strain to a given exercise bout. PURPOSE: To determine if the systemic assessment of the Pi:PCr ratio can serve as an indicator of respiratory stress. METHODS: Fourteen young males (age = 20.57 ± 1.22 yrs) completed a graded maximal exercise test (GXT) on a recumbent bike using either NB (n = 8) or combined (CB, n = 6) breathing. Plasma Pi and PCr were measured pre- and immediately post-GXT. Pi was analyzed using the malachite green colorimetric method, and PCr was quantified via sandwich enzyme-linked immunosorbent assay. The Pi:PCr was calculated by Pi ÷ PCr. A paired-sample t-test examined the Pi: PCr change following a GXT. A Pearson correlational analysis examined the relationship between the Pi:PCr and the respiratory performance during preset intensities (40%, 55%, 70%, 85%, and 100% VO2max). Data are presented as mean ± SD. RESULTS: The Pi:PCr ratio significantly decreased in the NB group (0.589 ± 0.313 to 0.530 ± 0.304, p = 0.034) mainly due to the elevated PCr (601.68 ± 318.88 mmol/L to 689.40 ± 410.60 mmol/L, p = 0.033). The Pi:PCR ratio was negatively correlated with VO2 only in the NB group throughout all preset intensities of the GXT. After controlling for the pre-GXT Pi:PCr as a covariate, the NB group showed a non-significant (p = 0.340) but higher mean concentration for post-exercise Pi:PCr compared to the CB group [NB: 0.451 ± 0.027 mmol/L versus CB: 0.407 ± 0.320 mmol/L. CONCLUSION: The results from the present study suggest that the assessment of the Pi:PCr ratio could serve as a valuable marker of physical strain pertaining to high respiratory demands. Moreover, the assignment of NB during exercise is becoming a novel method due to its postulated benefits towards respiratory function, which may induce a more significant cellular stress as denoted by an increase in the post-exercise Pi:PCr ratio

The Effect on Carbon Dioxide Production During Maximal Exercise with Distinct Breathing Mechanisms

Nasal breathing (NB) may lead to lower maximal oxygen uptake (VO2max) compared to oral breathing (OB) or nasal/oral combined breathing (CB) due to a transient increase in the systemic concentration of carbon dioxide (CO2) that can replicate the effects of a hypoxic environment. The exercise intensity at which NB can elicit this response is poorly understood. PURPOSE: To examine the increase in the fractional rate of exhaled CO2 (FECO2) and FEO2 with different breathing conditions during a graded maximal aerobic exercise test (GXT). METHODS: Eight healthy males (21.88 ± 0.46 years) completed 3 GXTs (separated by 48+ hours of recovery) using a different randomly assigned breathing condition (NB, OB, and CB). Participants exercised on a semi-recumbent bicycle at a pedaling speed of 70 rpm, increasing resistance every 2 minutes until volitional fatigue. Following the GXT, participants had a 2-minute recovery. Expired respiratory gases were collected via a metabolic cart. Six time points (40%, 55%, 70%, 85%, 100% VO2max, and recovery) were compared between NB, OB, and CB. Data are presented as mean ± SD. RESULTS: FECO2 was significantly higher during NB than OB at 70% [4.52 ± 0.37 vs. 4.07 ± 0.26%, p = 0.031 and 85% (4.49 ± 0.43% vs. 3.80 ± 0.32%, p = 0.009) of VO2max. Additionally, FECO2 at 100% of VO2max was significantly higher (p = 0.001) during NB (4.33 ± 0.69%) than OB (3.47 ± 0.29%) and CB (3.55 ± 0.19%). The transient change in FECO2 during exercise rapidly changed after the 2-minute recovery, where NB = 3.75 ± 0.71%, OB = 3.38 ± 0.17%, and CB = 3.30 ± 0.27%. FEO2 was significantly lower during NB than OB at 70% (16.34 ± 0.45% vs. 17.04 ± 0.3%, p = 0.011) and 85% (16.50 ± 0.53% vs. 17.32 ± 0.38%, p = 0.009) of VO2max. FEO2 was significantly lower (p = 0.003) during NB (16.66 ± 0.91%) compared to OB (17.67 ± 0.33%) and CB (17.61 ± 0.26%) at 100% VO2max. The transient change in FEO2 during exercise rapidly changed after the 2-minute recovery, where NB = 17.67 ± 1.00%, OB = 18.03 ± 0.23%, and CB = 18.20 ± 0.17%. CONCLUSION: NB elicits an exercised-induced increase in FECO2 that is analogous to a decrease in FEO2 starting at 70% of VO2max. Given the transient increase in FECO2, NB should be considered as a potential breathing method and further explored to replicate a temporary hypoxic environment that could promote a greater exercise adaptation than CB or OB might do

The Impact of Nasal Breathing During Exercise on Cerebral Blood Flow

Achieving hypercapnic-induced vasodilation while exercising can increase cerebral blood flow (CBF) to a greater extent than during normoxic conditions. Evidence suggests that nasal breathing during a maximal aerobic effort can elicit a hypercapnic condition. PURPOSE: To compare the effect of combined (CB), oral (OB), and nasal (NB) breathing on CBF during a graded maximal exercise test (GXT). METHODS: Six healthy males (age: 21.83 ± 1.00 years) abstained from physical activity and caffeine for 12+ hours prior to a GXT. Three GXTs were performed (48+ hours between each trial) using a different randomized breathing condition (CB, OB, and NB). After a warm-up, participants completed a GXT until volitional fatigue on a semi-recumbent bicycle. Stages lasted 2 minutes and increased by a pre-set wattage at 70 rpm. Respiratory gases were assessed via a metabolic cart. Throughout the GXT, ultrasound sonography (7.5 MHz linear transducer) was utilized to assess the peak systolic velocity (PSV) and vessel diameter of the internal (ICA) and external (ECA) carotid artery on the right side of the neck. A one-way ANCOVA with mean arterial blood pressure and oxygen uptake (VO2) as covariates was utilized to compare the three breathing patterns at 40%, 55%, 70%, 85%, and 100% of VO2max. Data are presented as mean ± SEM. RESULTS: The partial pressure of exhaled CO2 (PECO2) was significantly greater (p = 0.008) during NB (33.16 ± 1.37 mmHg) compared to CB (26.63 ± 1.32 mmHg) and OB (26.72 ± 1.37) at 100% VO2max. While not statistically significant, there was a greater PSV in the ICA during NB (99.72 ± 7.12 cm/s) compared to CB (87.34 ± 9.36 cm/s) and OB (89.63 ± 9.77 cm/s) at 100% VO2max. Similarly, there was a greater PSV in the ICA during NB (102.53 ± 8.07 cm/s) compared to CB (93.13 ± 7.79 cm/s) and OB (81.25 ± 7.80 cm/s) at 85% VO2max. In contrast, there was a significantly greater (p = 0.027) PSV in the ICA during NB (126.12 ± 7.51 cm/s) compared to OB (92.47 ± 7.34 cm/s) but not CB (111.91 ± 7.14 cm/s) at 70% VO2max. There were no significant differences in the PSV of the ECA nor the diameter of the ICA and ECA. CONCLUSION: NB during a GXT increased PSV in the ICA compared to CB and OB, which might be partly related to an increased systemic concentration of CO2. A greater increase in PSV in the ICA represents a greater CBF that might provide greater cognitive health benefits than while exercising with either CB or OB. Studies with a bigger sample size will provide greater statistical power to examine the benefits of increasing the PSV in the ICA and its effect on cognitive health

Relationships Between Anthropometric Variables and the Internal Carotid Blood Flow

Assessment of peak systolic velocity (PSV) of the internal carotid artery (ICA) is utilized to examine stroke-symptomatic individuals for ICA stenosis. While a sedentary lifestyle is a common risk factor for ICA stenosis, a deeper understanding of how body composition affects ICA blood flow could provide insights before symptoms appear. PURPOSE: To examine the relationship between ICA blood flow and body composition variables. METHODS: ICA blood flow was assessed in eight healthy males (21.88 ± 2.25 years) on three different days to control for possible diurnal variability that could affect blood flow. Participants abstained from caffeine and physical activity for a minimum of 12 hours prior to each visit. Dual-energy X-ray absorptiometry was used to assess body fat percentage (BF%) and visceral fat area (VFA). Bioelectrical impedance (BIA) was used to assess body water percentage (BW%), metabolic age (MetA), and visceral fat rating (VFR). Participants rested supine with eyes closed for 5 minutes prior to assessment of ICA. B-mode doppler ultrasound sonography (7.5 MHz linear transducer) was used to measure PSV, end-diastolic velocity (EDV), resistance index (RI), and vessel diameter on the right ICA after 2 minutes of continual scanning with a 60° insonation angle. The relationship between ICA blood flow and body composition variables was examined via Pearson correlation analysis. RESULTS: BF% was positively correlated with ICA EDV (r = 0.669, p \u3c 0.001) and ICA PSV (r = 0.416, p = 0.043) but negatively correlated with ICA diameter (r = -0.424, p = 0.039). VFA was positively correlated with ICA EDV (r = 0.505, p = 0.012). BW% was negatively correlated with ICA PSV (r = -0.417, p = 0.043) and EDV (r = -0.620, p \u3c 0.001). MetA was positively correlated with ICA EDV (r = 0.630, p \u3c 0.001) but negatively correlated with ICA RI (r = -0.509, p = 0.011) and diameter (r = -0.513, p = 0.010). Similarly, VFR was positively correlated with ICA EDV (r = 0.644, p \u3c 0.001) but negatively correlated with ICA RI (r = -0.511, p = 0.011) and diameter (r = -0.496, p = 0.014). CONCLUSION: EDV has a greater correlation with body composition than PSV, suggesting that adiposity-related factors can describe ICA blood flow. Similarly, BIA might offer a solid and easy-to-attain procedure to indirectly assess ICA blood flow that warrants further research

Evaluation of Body Fat Percentage with Vertical and Longitudinal Skinfolds

Subcutaneous fat content, as well as body fat percentage (BF%), can be effectively assessed using skinfold calipers. While skinfolds (SFs) are practical and easy to attain, their accuracy could be reduced if the SFs are not collected with the ideal fold orientation. PURPOSE: To determine if vertical or longitudinal SFs in the trunk area are better predictors of BF%. METHODS: A pool of thirty-eight male (21.29 ± 4.59 yrs, 15.68 ± 4.82 BF%) and twenty-two female (21.14 ± 4.05 yrs, 26.63 ± 5.34 BF%) participants completed the study. A dual-energy X-ray absorptiometry scan was utilized to assess BF%. Using a Lange caliper, one technician assessed all SFs within the trunk in triplicate using both a vertical pinch and a longitudinal pinch. SFs sites included: 2 cm left, right, superior, and inferior of the umbilicus; left and right anterior mid-axillary line at the level of the navel; 2 cm left and right of the vertebral column at the level of the navel; midsternal line at the slimmest part of the waist and at the level of the xiphoid process. In addition, two commonly assessed diagonal folds (right suprailiac and subscapular) were collected. The relationship between SFs orientation and BF% was assessed utilizing a Pearson correlation. Stepwise linear regression was utilized to predict BF%. Data are presented as mean ± SD. RESULTS: Overall, vertical folds for both males and females had a higher correlation with BF% than longitudinal folds. The right vertical mid-axillary (RVMA) SFs had a significant correlation with BF% for both male (r = 0.864, p \u3c 0.001) and female (r = 0.712, p \u3c 0.001) participants. Similarly, the subscapular (SS) SFs had a significant correlation with BF% for both male (r = 0.851, p \u3c 0.001) and female (r = 0.788, p \u3c 0.001) participants. BF% was successfully predicted [4.142 + (10.154 * Sex) + (0.255 * RVMA) + (0.516 * SS), adjusted R2 = 0.874], where sex (0 = male, 1 = female). The average RVMA SFs were 18.43 ± 7.85 mm for males and 19.91 ± 6.78 mm for females, while the SS SFs were 13.50 ± 4.95 mm for males and 14.05 ± 5.34 mm for females. CONCLUSION: Although RVMA SFs are not commonly utilized to estimate BF%, there is evidence of a high correlation with BF%. The applicability of utilizing the RVMA jointly with the SS SFs as a fast yet reliable method to estimate BF% should be examined in a large and diverse cohort

Describing Visceral Fat via Girth and Skinfold Measurements

While girth ratios (GR), such as waist-to-height ratio (WHtR) and waist-to-hip ratio (WHR), and body fat percentage (BF%) have been widely used to describe visceral fat (VF), the applicability of skinfold (SF) measurements has been given less attention for the same purpose. PURPOSE: This study examined the associations between BF%, GR, SF, and VF. METHODS: Sixty healthy participants (38 males and 22 females, age = 21.23 ± 4.37 years, BMI = 24.87 ± 3.02 kg/m2, BF% = 19.70 ± 7.28%) participated in the study. Girth ratios, including WHtR and WHR, were assessed using a Gulick tape specifically at the level of the navel and slimmest part of the waist. SF thickness was assessed using a Lange skinfold caliper at 5 different regions, including the navel, upper abdomen, axillary, lumbar, and subscapular. Dual-energy X-ray absorptiometry was used to determine VF. A Pearson correlation was utilized to examine the associations among BF%, GR, SF, and VF. RESULTS: Females’ VF (33.9 ± 16.9 cm2) was significantly correlated with BMI (23.9 ± 3.7 kg/m2, r = .451, p = .035) and BF% (26.6 ± 5.3%, r = .590, p = .004), while males’ VF (49.6 ± 10.9 cm2) was not correlated with BMI (25.4 ± 2.4 kg/m2, r = -.021, p = .899) nor BF% (15.7 ± 4.8%, r = -.084, p = .616). In addition, WHR (.85 ± .04) was correlated with VF in males (r = .462, p = .004), while WHtR (.47 ± .06) was correlated with VF (r = .616, p = .002) in females. When participants were clustered into two groups based on BMI (\u3c 25 or ≥ 25 kg/m2), VF was correlated with the WHR in males (n = 18) with a BMI ≥ 25 kg/m2 (r = .522, p = .026) and in women (n = 14) with a BMI \u3c 25 kg/m2 (r = .567, p = .035). However, males (n = 20) with a BMI \u3c 25 kg/m2 and women (n = 8) with a BMI ≥ 25 kg/m2 had no correlations between VF and any GR or SF measurements. Although there was no correlation between VF and SF in males, VF in females was correlated with SF at the anterior slimmest part of the waist (16.1 ± 4.9 mm, r = .450, p = .035), iliac crest (14.0 ± 5.4 mm, r = .527, p = .012), and subscapular (14.0 ± 5.3 mm, r = .51, p = .018). CONCLUSION: BF% has a greater correlation with VF in females than in males, while WHR (a marker of body fat distribution) better explains VF in males. In addition, SF only held a degree of applicability within females. Furthermore, fat content seems to play a more important role in females when assessing VF content, while fat distribution seems to be more important in males

Responses of Inflammatory Biomarkers in Circulation and Peripheral Blood Mononuclear Cell to Maximal Exercise with Nasal Breathing

There is growing interest in utilizing nasal breathing (NB) in exercise routines to improve performance. However, there is uncertainty on the impact of such exercise on inflammatory biomarkers in circulation and peripheral blood mononuclear cells (PBMCs), which play a significant role in immune response. PBMCs can undergo functional changes from interactions with exercise-related cytokines, potentially inducing a more efficient immune response. PURPOSE: This study examined the acute responses of pro- and anti-inflammatory cytokines in circulation and PBMCs following a maximal exercise with NB. METHODS: Eleven physically healthy, sedentary men (age = 20.63 ± 1.36, BMI = 26.03 ± 3.16 kg/m2, and VO2max = 32.60 ± 6.46 mL/kg/min) were randomly assigned to the NB (N=6) or the combined breathing (CB, N = 5) group and performed a maximal graded exercise on a recumbent bike. Blood samples were collected to the vacutainer tubes containing EDTA to separate plasma and PBMCs before and immediately following the maximal exercise. PBMCs were isolated using density gradient centrifugation over Lymphoprep. The acute changes in pro- (IL-6 and IL-1β) and anti-inflammatory cytokines (IL-10) were measured in both plasma and PBMCs. RESULTS: The concentration of PBMC cytokines was significantly lower, ranging from 5 to 22 times, than the plasma cytokine concentrations. The plasma vs. PBMC cytokine concentrations were as follows: IL-6 (10.10 ± 9.3 vs. 1.92 ± 1.55 pg/mL, p = 0.001), IL-10 (18.18 ± 17.66 vs. 2.55 ± 1.41 pg/mL, p = 0.008) and IL-1b (17.73 ± 16.77 vs. 0.80 ± 0.82 pg/mL p = 0.008, p = 0.004). No significant changes in either plasma or PBMC IL-10 and IL-1β were observed immediately following the maximal exercise or between the NB and CB groups, whereas PBMC IL-6 was significantly lower in the NB (1.24 ± 1.27 pg/mL, p = 0.029) than the CB (2.79 ± 1.5 pg/mL) group. CONCLUSION: The current study found that the concentrations of cytokines in PBMCs were significantly lower than those in circulation. Furthermore, the lower levels of pro-inflammatory cytokine, such as PBMC IL-1β, associated with NB exercise imply potential immune health benefits. Further research is essential to better understand and validate these findings using different exercise modalities in various subject groups. Doing so will determine whether this benefit of adding nasal breathing to exercise can extend to larger patient populations

A framework of transient hypercapnia to achieve an increased cerebral blood flow induced by nasal breathing during aerobic exercise

During exercise, cerebral blood flow (CBF) is expected to only increase to a maximal volume up to a moderate intensity aerobic effort, suggesting that CBF is expected to decline past 70 % of a maximal aerobic effort. Increasing CBF during exercise permits an increased cerebral metabolic activity that stimulates neuroplasticity and other key processes of cerebral adaptations that ultimately improve cognitive health. Recent work has focused on utilizing gas-induced exposure to intermittent hypoxia during aerobic exercise to maximize the improvements in cognitive function compared to those seen under normoxic conditions. However, it is postulated that exercising by isolating breathing only to the nasal route may provide a similar effect by stimulating a transient hypercapnic condition that is non-gas dependent. Because nasal breathing prevents hyperventilation during exercise, it promotes an increase in the partial arterial pressure of CO2. The rise in systemic CO2 stimulates hypercapnia and permits the upregulation of hypoxia-related genes. In addition, the rise in systemic CO2 stimulates cerebral vasodilation, promoting a greater increase in CBF than seen during normoxic conditions. While more research is warranted, nasal breathing might also promote benefits related to improved sleep, greater immunity, and body fat loss. Altogether, this narrative review presents a theoretical framework by which exercise-induced hypercapnia by utilizing nasal breathing during moderate-intensity aerobic exercise may promote greater health adaptations and cognitive improvements than utilizing oronasal breathing