Byrd, M. Travis

AbstractIntermittent hypoxia has been used to enhance oxygen delivery in athletes and patients; however, it is unclear whether acute exposure is sufficient to elicit lasting physiologic adaptation(s). The purpose of this study was to evaluate physiologic response(s) to hypobaric‐hypoxic (HH) exercise. Nine participants (4 M/5F; 37.9 ± 12.7 yrs.; 174.3 ± 9.4 cm; 75.3 ± 15.9 kg; 24.4 ± 3.4 kg/m2) were exposed to progressively higher simulated altitudes and completed two HH submaximal exercise sessions (~30 min ea., ≥72 h apart) on a cycle ergometer at the first altitude that posed a significant challenge to them. Altitude was dependent on individual response as determined from heart rate (HR), peripheral oxygenation (SpO2), and the ratio of HR response to SpO2 (HR/SpO2). Statistical analyses included paired samples t‐test (p ≤ 0.05). No significant change in SpO2 (HH‐1: 85 ± 4% vs. HH‐2: 85 ± 4%, p = 0.684) was observed between sessions. However, there were significant decreases in: HR (HH‐1: 150 ± 18 bpm vs. HH‐2: 133 ± 27 bpm, p = 0.001) of 18 bpm (11%); HR/SpO2 (HH‐1: 1.76 ± 0.22 vs. HH‐2: 1.57 ± 0.33, p = 0.012); and RPE (HH‐1: 15 ± 2 vs. HH‐2: 11 ± 4, p = 0.017). While workload significantly increased (HH‐1: 89 ± 36 W vs. HH‐2: 105 ± 36 W, p = 0.024). Some participants had a threshold/challenging altitude, but from a single bout there is evidence of improved tolerance that can last over a week. Further investigation is required to replicate and understand possible mechanisms.

Abstract Anderson, AlOK, Voskuil, CC, Byrd, MT, Garver, MJ, Rickard, AJ, Miller, WM, Bergstrom, HC, and Dinyer McNeely, TK. Affective and perceptual responses during an 8-week resistance training to failure intervention at low vs. high loads in untrained women. J Strength Cond Res 37(3): 546–554, 2023—This study examined the effects of resistance training (RT) to failure on the perceptual and affective responses, intent-to-continue RT to failure in a self-initiated session, and affect-intent relationship. Twenty-three untrained women (mean ± SD : age 21.2 ± 2.2 years; height 167 ± 5.7 cm; body mass, 62.3 ± 16.2 kg) completed an 8-week, full-body RT to failure intervention at a low (30% 1RM; n = 11) or high (80% 1RM; n = 12) load. The Borg’s rating of perceived exertion (RPE) scale was used to assess the acute (aRPE) and session (sRPE) RPE immediately after repetition failure and each training session, respectively. Immediately, 15-minute, and 60-minute postsession affective responses were assessed using the feeling scale (FS; −5 to +5), and intent to continue to RT was assessed on a scale of 0–100% intention. During week 4 (W4) and week 8 (W8), aRPE (W4: 18 ± 2, W8: 18 ± 2; p ≤ 0.032) and sRPE (W4: 17 ± 2, W8: 18 ± 1; p ≤ 0.018) were greater than that during week 1 (W1; aRPE: 17 ± 2; sRPE: 16 ± 2). The FS responses increased from immediately to 60-minute postsession during W4 ( p ≤ 0.019) and W8 ( p ≤ 0.049). The correlation between affect and intent-to-continue RT increased from W1 ( r = 0.416) to W8 ( r = 0.777). Regardless of load, untrained women reported similar perceptual, affective, and intention responses. These variables should be considered to improve RT program adoption and adherence in women.

Many individuals travel to high altitude each year. Acclimatization to altitude occurs over the course of several days as the body adequately adapts to function in an environment with reduced partial pressure of oxygen. However, with a faster accent to attitude, comes an increased potential for maladaptations to occur, leading to the development of acute mountain sickness (AMS). Each year scientists and support workers are transported by plane from McMurdo Station in Antarctica (sea level) to the Amundsen‐Scott South Pole Station (2835m). This uniform and rapid deployment to altitude provides a unique opportunity to study the effects of hypobaric hypoxia on gene expression, which may help to illustrate the body’s ability to acclimatize to these environmental conditions. Purpose To detect pathway specific gene expression changes associated with the development of AMS and help identify potential targets that may aid in the prediction of risk in the development of AMS symptoms due to rapid exposure to high altitude. Methods Venous blood samples were collected from 53 (height 176.65±8.91cm, weight: 80.49±14.36kg) healthy subjects (38 (27 males; 11 females) that did not develop AMS and 15 (10 males; 5 females) that did develop AMS, as defined by the Lake Louis symptom questionnaire, collected at 2 different time points, with the first being at sea level and the second being after 48hr of altitude exposure). Microarray analysis was performed on the peripheral blood mononuclear cells (PBMCs) from the collected samples, and a logistic regression was performed to determine probe set association with AMS. Results There was a total of 178 significant (p<0.05) probe sets, with 156 of the probe sets being associated with AMS and 22 of the probe sets being associated with no AMS. The probe sets were entered into the Reactome Pathway Database (reactome.org). Pathways identified in association with AMS involved immune system pathways (interleukin signaling) and cellular responses to stimuli pathways (oxidative stress induced senescence signaling), and gene transcription pathways (mitochondrial biogenesis signaling, differentiation of hematopoietic stem cells). Interestingly, pathways identified in association with no development of AMS involved cell cycling pathways (mitotic signaling), chromatin organization pathways (chromatin modifying enzymes), metabolism pathways (utilization of ketone bodies) and the circadian clock pathway (circadian gene expression signaling). Conclusion These findings indicate potential maladaptive responses within the immune system and mitochondrial function, may play a key role in why some individuals develop AMS symptoms. An individual’s ability to sufficiently utilize different metabolic fuel sources and adapt their circadian rhythm may also prevent the development of AMS symptoms.

Abstract Succi, PJ, Dinyer, TK, Byrd, MT, Voskuil, CC, and Bergstrom, HC. Application of V̇ o 2 to the critical power model to derive the critical V̇ o 2 . J Strength Cond Res 36(12): 3374–3380, 2022—The purposes of this study were to (a) determine whether the critical power (CP) model could be applied to V̇ o 2 to estimate the critical V̇ o 2 (CV̇ o 2 ) and (b) to compare the CV̇ o 2 with the V̇ o 2 at CP (V̇ o 2 CP), the ventilatory threshold (VT), respiratory compensation point (RCP), and the CV̇ o 2 without the V̇ o 2 slow component (CV̇ o 2 slow). Nine subjects performed a graded exercise test to exhaustion to determine V̇ o 2 peak, VT, and RCP. The subjects performed 4 randomized, constant power output work bouts to exhaustion. The time to exhaustion (T Lim ), the total work (W Lim ), and the total volume of oxygen consumed with (TV̇ o 2 ) and without the slow component (TV̇ o 2 slow) were recorded during each trial. The linear regressions of the TV̇ o 2 vs. T Lim , TV̇ o 2 slow vs. T Lim , and W Lim vs. T Lim relationship were performed to derive the CV̇ o 2 , CV̇ o 2 slow, and CP, respectively. A 1-way repeated-measures analysis of variance ( p ≤ 0.05) with follow-up Sidak-Bonferroni corrected pairwise comparisons indicated that CV̇ o 2 (42.49 ± 3.22 ml·kg −1 ·min −1 ) was greater than VT (30.80 ± 4.66 ml·kg −1 ·min −1 ; p < 0.001), RCP (36.74 ± 4.49 ml·kg −1 ·min −1 ; p = 0.001), V̇ o 2 CP (36.76 ± 4.31 ml·kg −1 ·min −1 ; p < 0.001), and CV̇ o 2 slow (38.26 ± 2.43 ml·kg −1 ·min −1 ; p < 0.001). However, CV̇ o 2 slow was not different than V̇ o 2 CP ( p = 0.140) or RCP ( p = 0.235). Thus, the CP model can be applied to V̇ o 2 to derive the CV̇ o 2 and theoretically is the highest metabolic steady state that can be maintained for an extended period without fatigue. Furthermore, the ability of the CV̇ o 2 to quantify the metabolic cost of exercise and the inefficiency associated with the V̇ o 2 slow component may provide a valuable tool for researchers and coaches to examine endurance exercise.