Effects of induced local ischemia during a 4-km cycling time trial on neuromuscular fatigue development

No sex differences in performance and perceived fatigability during a self-paced endurance exercise performed under moderate hypoxia

This study examined potential sex differences in performance and perceived fatigability during a whole body endurance exercise performed under normoxia or moderate hypoxia. Nine males and eight females cyclists performed a 4-km cycling time trial under normoxia or hypoxia conditions. Performance fatigability and its central and peripheral determinants were measured via pre- to post-exercise changes in maximal voluntary isometric contraction (IMVC), voluntary activation (VA), and potentiated twitch force (TwPt) of knee extensors, respectively. Perceived fatigability was characterized via a rating of perceived exertion (RPE). Time to complete the trial was longer in hypoxia than normoxia in females (482 ± 24 vs. 465 ± 21 s) and males (433 ± 30 vs. 408 ± 31 s) (P = 0.039). There was no effect of sex or condition (P ≥ 0.370) for the magnitude of decrease in IMVC (female: normoxia = -14.3 ± 4.4%, hypoxia = -11.8 ± 5.2% vs. male: normoxia = -13.1 ± 9.4%, hypoxia = -12.9 ± 9.8%), TwPt (female: normoxia = -34.4 ± 11.4%, hypoxia = -31.8 ± 18.9% vs. male: normoxia = -30.5 ± 17.9%, hypoxia = -31.9 ± 20.9%), and VA (female: normoxia = -0.5 ± 2.3%, hypoxia = -1.6 ± 1.6% vs. male: normoxia = 0.8 ± 2.2%, hypoxia = -0.5 ± 1.3%). RPE was higher in hypoxia than in normoxia for both groups (P = 0.002). In conclusion, moderate hypoxia similarly impairs performance and perceived fatigability development in females and males during a 4-km cycling time trial.NEW & NOTEWORTHY In this study, we showed that females and males develop a similar hypoxia-induced impairment in endurance performance, perceived and performance fatigability during a 4-km cycling time trial. These novel findings indicate that females and males regulate their power output similarly during a 4-km cycling time trial under moderate hypoxia, likely to avoid prematurely exacerbating metabolic disturbances and thereby reaching comparable levels of performance fatigability by the end of the task.

Prior Involvement of Central Motor Drive Does Not Impact Performance and Neuromuscular Fatigue in a Subsequent Endurance Task

PURPOSE

This study evaluated whether central motor drive during fatiguing exercise plays a role in determining performance and the development of neuromuscular fatigue during a subsequent endurance task.

METHODS

On separate days, 10 males completed three constant-load (80% peak power output), single-leg knee-extension trials to task failure in a randomized fashion. One trial was performed without preexisting quadriceps fatigue (CON), and two trials were performed with preexisting quadriceps fatigue induced either by voluntary (VOL; involving central motor drive) or electrically evoked (EVO; without central motor drive) quadriceps contractions (~20% maximal voluntary contraction (MVC)). Neuromuscular fatigue was assessed via pre-post changes in MVC, voluntary activation (VA), and quadriceps potentiated twitch force ( Qtw,pot ). Cardiorespiratory responses and rating of perceived exertion were also collected throughout the sessions. The two prefatiguing protocols were matched for peripheral fatigue and stopped when Qtw,pot declined by ~35%.

RESULTS

Time to exhaustion was shorter in EVO (4.3 ± 1.3 min) and VOL (4.7 ± 1.5 min) compared with CON (10.8 ± 3.6 min, P < 0.01) with no difference between EVO and VOL. ΔMVC (EVO: -47% ± 8%, VOL: -45% ± 8%, CON: -53% ± 8%), Δ Qtw,pot (EVO: -65% ± 7%, VOL: -59% ± 14%, CON: -64% ± 9%), and ΔVA (EVO: -9% ± 7%, VOL: -8% ± 5%, CON: -7% ± 5%) at the end of the dynamic task were not different between conditions (all P > 0.05). Compared with EVO (10.6 ± 1.7) and CON (6.8 ± 0.8), rating of perceived exertion was higher ( P = 0.05) at the beginning of VOL (12.2 ± 1.0).

CONCLUSIONS

These results suggest that central motor drive involvement during prior exercise plays a negligible role on the subsequent endurance performance. Therefore, our findings indicate that peripheral fatigue-mediated impairments are the primary determinants of high-intensity single-leg endurance performance.

Comparing muscle VO2 from near-infrared spectroscopy desaturation rate to pulmonary VO2 during cycling below, at and above the maximal lactate steady state

Muscle oxygen uptake (V̇O_2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇O_2m. However, its correspondence with pulmonary oxygen uptake (V̇O_2p) during exercise remains unknown.

PURPOSE

to investigate the V̇O_2m and V̇O_2p relationship in females and males in response to prolonged constant-load cycling exercise at different intensities.

METHODS

Eighteen participants (8 females) visited the laboratory on six occasions: 1) ramp incremental test; 2-3) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); 4-6) constant-PO exercise bouts to task failure at (i) 15% below MLSS (MLSS_-15%); (ii) MLSS; (iii) 15% above MLSS (MLSS_+15%). V̇O_2m was estimated at baseline, at min 5, 10, 20, 30, and at task failure. V̇O_2p was continuously recorded during the constant-PO bouts.

RESULTS

V̇O_2pand V̇O_2m significantly increased from min 5 to min 30 in MLSS condition (all p < 0.05) and from min 5 to min 10 in MLSS_+15% condition (all p < 0.05). V̇O_2pand V̇O_2m were correlated (r² adj range of 0.70-0.98, all p < 0.001) amongst exercise intensities in both females and males. Additionally, both variables were also correlated when expressed as percent (r² adj range of 0.52-0.77, all p < 0.001).

CONCLUSION

V̇O_2p and V̇O_2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇O_2p andV̇O_2m were correlated regardless the exercise intensity and sex of the participants.

Intervention Effect of Long-Term Aerobic Training on Anxiety, Depression, and Sleep Quality of Middle School Students With Depression After COVID-19

Objective: To explore the effects of using RPE exercise intensity monitoring methods and 12-week mid- and low-intensity team aerobic training on anxiety, depression and sleep quality of depressed middle school students after the COVID-19 epidemic. Methods: All study participants were all from a boarding middle school in Chongqing, China. All study participants were screened by the self-rating depression scale and reached the diagnostic criteria for depression. The study subjects were divided into a control group (N = 35) and an exercise group (N = 34). The exercise group performed 30-min night aerobic running four times a week. Use the Borg 6-20 rating of perceived exertion scale (RPE) as a monitoring tool for exercise intensity, and control the exercise intensity at RPE = 11-14. And the control group studied and lived normally. The experiment lasted 12 weeks in total. After the experiment, there were 34 people in the control group and 23 people in the exercise group. The subjects' anxiety, depression and Pittsburgh sleep quality were scored before and after the experiment. Results: After intervention, the depression index (p < 0.01) of the exercise group was significantly lower than that of the control group. Conclusion: Using the RPE exercise intensity monitoring method for 12 weeks of mid- and low-intensity team aerobic training can improve the depressive symptoms of depressed middle school students, and it is beneficial to improve the students' mental health.