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Activities of daily living are characterized by continuous changes in exercise intensity and duration resulting in many abrupt changes in metabolic demand. The ability to readily meet these demands is described by the rate of adaptation in oxygen uptake measured at either the mouth (VO2p) or at the site of active muscle. Many studies have used a single step transition to assess this rate of adaptation. However, a continually changing exercise, such as a pseudorandom binary sequence (PRBS) protocol, provides more transition phases to analyze. We examined the VO2p and microvascular oxygenation responses using near infrared spectroscopy (NIRS) during PRBS exercise. Five healthy males (30 ± 6 yrs, 83.4 ± 20.9 kg, VO2pk, 38.9 ± 5.9 mL/kg/min; mean ± SD) completed a ramp exercise to fatigue for the determination of the lactate threshold (LT) and peak VO2p (VO2pk). Each bout of PRBS exercise transitioned from a baseline of 20 W to a WR corresponding to either 90% of LT (MOD, 100 ± 7 W)) or to a WR at 40% of the difference between LT and VO2pk (HVY, 173 ± 13 W). The PRBS exercise consisted of 30 units of 15 s that alternated between BSL and the higher WR in a pseudorandom pattern; the pattern was repeated 3 times. VO2p was measured breath‐by‐breath using a metabolic cart and interpolated to 1 s intervals. For each subject and WR, the 3 repetitions for each trial were ensembled averaged yielding a single 450 s response. Changes in hemoglobin oxygenation (deoxy‐[Hb+Mb]) and total hemoglobin concentration ([THC]) were measured from the vastus lateralis (VL) using frequency‐domain NIRS. Data were collected at 1 Hz and ensembled averaged to yield a single 450 s response. VO2p and deoxy‐[Hb+Mb] responses were transformed into the frequency domain and analyzed using standard approaches and the mean‐normalized gain (MNG). The harmonic amplitudes (Amph) for VO2p/WR were lower (p<0.05) during HVY at 0.0067 Hz (Mod, 56.9 ± 13.0 %; HVY, 49.3 ± 6.8 %), 0.011 Hz (Mod, 37.6 ± 17.0 %, HVY: 25.8 ± 5.7 %) and 0.013 Hz (Mod, 33.2 ± 12.8 %; HVY, 15.8 ± 10.2 %). The Amph for deoxy‐[Hb+Mb]/WR were lower (p<0.05) for VO­2p/WR in HVY compared to MOD (Mod, 39.5 ± 6.0 %; HVY, 30.2 ± 3.9 %). MNG was also lower (p<0.05) for deoxy‐[Hb+Mb]/WR in HVY compared to MOD (Mod, 77.4 ± 26.6 %; HVY, 47.3 ± 10.0 %). The VO2p and deoxy‐[Hb+Mb] responses from a PRBS trial represent the responses to individual sinusoidal inputs at each frequency tested. The normalized Amph and MNG measured in the current study described the temporal dynamics of the variables of interest (i.e., VO2p and deoxy‐[Hb+Mb]). The results of the current study showed a significant decrease in both normalized Amph and MNG for VO2p and deoxy‐[Hb+Mb] suggesting that exercise performed above the LT results in a slowing of both the VO2p and microvascular deoxy‐[Hb+Mb] responses. These findings are consistent with previous studies demonstrating a slowing of VO2p above the LT. Compared to studies using a single step protocol, responses to PRBS protocols include many transition periods to identify...

Dietary nitrate supplementation in the form of beetroot juice has been the subject of numerous studies in recent literature with inconclusive results. Beetroot juice (BRJ) has been consistently tested using constant‐load or maximal‐exertion exercise, but the influence of nitrate on pulmonary oxygen uptake (VO2p) and microvascular oxygenation to continually‐changing exercise demands has received less attention. Five healthy males (30 ± 6 yrs, 83.4 ± 20.9 kg, VO2pk, 38.9 ± 5.9 mL/kg/min; mean ± SD) completed a ramp exercise to fatigue for the determination of the lactate threshold (LT) and peak VO2p (VO2pk). Each bout of PRBS exercise transitioned from a baseline of 20 W to a WR corresponding to 90% of LT (MOD, 100 ± 7 W). The PRBS exercise consisted of 30 units of 15 s that alternated between BSL and 90% LT in a pseudorandom pattern; the pattern was repeated 3 times. VO2p was measured breath‐by‐breath using a metabolic cart and interpolated to 1 s intervals. For each subject and WR, the 3 repetitions for each trial were ensemble averaged yielding a single 450 s response. Changes in hemoglobin oxygenation (deoxy‐[Hb+Mb]) and total hemoglobin concentration ([THC]) were measured from the vastus lateralis (VL) using frequency‐domain NIRS. Data were collected at 1 Hz and ensemble averaged to yield a single 450 s response. VO2p gain was calculated in the time domain by dividing the ΔVO2p by the ΔWR. VO2p and deoxy‐[Hb+Mb] responses were transformed into the frequency domain and analyzed using standard approaches and the mean‐normalized gain (MNG). Subjects completed the first trial under control conditions (CON), and then were put on a dosing regimen of 400mg of dietary nitrate (Beet It! Beetroot Juice) 2x/day for 3 days before returning to the lab for the second trial (BRJ). The gain (VO2/WR) was decreased in the BRJ condition versus CON (CON: 5.58 ± 0.65 mL/min/W, BRJ: 4.66 ± 1.03 mL/min/W, p = 0.049). The VO2 harmonics were not different between conditions. The deoxy‐[Hb+Mb] harmonics were lower at all frequencies in the BRJ condition versus CON (p < 0.05). MNG is a measure that isolates the temporal characteristics of the investigated variable, using a normalization procedure. MNG for VO2 was not significantly different between conditions. The deoxy‐[Hb+Mb] MNG was lower in BRJ (CON: 77.4 ± 26.6 %, BRJ: 42.3 ± 11.8 %, p = 0.011). The results of the current study are consistent with previous studies showing that BRJ supplementation decreases the oxygen cost of exercise for a given work rate. The similarity in the harmonics and the MNG for VO2 suggest that there was no impact of BRJ on the speed of VO2 adaptation, but the significant decrease in the MNG for the deoxy‐[Hb+Mb] suggests that the rate of adaptation of deoxy‐[Hb+Mb] was slower in the BRJ condition. The PRBS protocol has many on‐ and off‐transitions that may identify influences of dietary nitrate that are not discernable during the rapid adaptation of deoxy‐[Hb+Mb] to a single‐step transition. Additionally, the results of the current study indicate that fur...

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An individual typically experiences a wide range of metabolic demands during a normal day. Rarely does a person perform abrupt changes in physical activity nor does the demand last for a long period of time at that same intensity. However, much of the research into the control of oxygen uptake (VO2) kinetics has utilized square wave, constant load exercise to understand the underlying physiological responses to exercise. This study examined the integrated response of pulmonary VO2, microvascular oxygenation measured using near‐infrared spectroscopy (NIRS) and muscle activation using surface electromyography (sEMG) techniques during sinusoidal cycling where the exercise intensity continuously changes. Ten male subjects (age, 30 ± 9 yrs (±SD); height, 179 ± 8 cm; weight, 89.9 ± 18.7 kg) completed a maximal exercise test to determine the lactate threshold (LaT) and peak VO2 (VO2pk). Each subject completed 2 trials consisting of 4 min of cycling at 20 W followed by 4 bouts of sinusoidal cycling transitions. The work rate transitioned between 30 W and a work rate corresponding to 70% of the difference between the LaT and VO2pk (Δ70) as a sinewave function. Pulmonary VO2 was measured breath‐by‐breath using a metabolic cart, interpolated to 1 s and ensemble averaged to yield a single sinewave for analysis. Changes in hemoglobin oxygenation ([HHb]) and total hemoglobin concentrations [(THC)] were measured from VL using NIRS. Data were collected at 1 Hz and ensemble averaged to yield a single sinewave for analysis. Muscle activation (vastus medialis (VM), vastus lateralis (VL)) was assessed using sEMG and reported as the root mean square (RMS). The RMS of the VL and VM were divided into 5 s bins and compared at each crest (CR) and trough (TR) during the 4 sinewaves. The group mean transition in work rate from the TR to the crest CR of each sinewave was 208 ± 27 W. No difference in muscle activation was observed at the CR of each sinewave as shown by the similar RMS for VL and VM. Compared to baseline (1064 ± 136 ml/min), there was a significant (p<0.05) increase in VO2 (2567 ± 322 ml/min) that was 220 ml lower (p<0.05) than the predicted VO2 (assuming 10 ml/min/W) for the work rate (2788 ± 271 ml/min). VO2 did not return to baseline values during the TR (1806 ± 223 ml/min, p<0.05) resulting in an lower gain for VO2 than expected (4.7 ± 1.0 ml/min/W). A significant phase lag was observed for VO2 of 64.9 ± 14.0 deg. Mean [HHb] increased (p<0.05) from baseline (12.4 ± 2.9 μM) to the CR of the sinewave (17.7 ± 7.8 μM). Similar to VO2, there was a significant phase lag observed for [HHb] of 56.9 ± 16.0 deg. The difference in phase lag responses between VO2 and [HHb] was not different. These findings are consistent with previous studies reporting a lower gain and a significant phase lag for VO2 during sinewave exercise. Compared to studies utilizing square wave exercise which have shown [HHb] to adapt much faster than VO2, the similar phase lag for VO2 and [HHb] observed in the present study suggests that VO2 and [HHb] respond similarly to the increase in exercise intensity during sinewave exercise. Further investigations into the integration of VO2 and [HHb] during exercise that is continuously changing intensities are warranted.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.