Nervous system differences between the sexes and across the menstrual cycle

Sex hormones have in vitro effects on the nervous system. Furthermore, the effects of estradiol and progesterone metabolites have neurologic responses on the motor system, evidenced by transcranial magnetic stimulation studies. Sex hormone effects on the nervous system may underlie some of the sex discrepancies seen in athletic performance, injury and cardiovascular events. Investigating sex differences is often complicated by hormonal oscillations across the menstrual cycle; therefore, the aims of this research were to investigate sex and menstrual cycle effects on the motor and cardiovascular systems and the interaction of these two systems. In study 1, motor unit (MU) recruitment patterns of the vastus medialis (VM) and vastus medialis oblique (VMO) were examined in males and females at five menstrual cycle phases. Initial discharge rate between the VM and VMO were different only in females. This VM/VMO discharge discrepancy was only evident in females during the ovulatory and mid luteal menstrual phases. Study 2 examined the frequency domain relationship of the VM and VMO MUs between the sexes and across the menstrual cycle. Males have 256% to 741% greater odds of having coherent MU oscillations in the common drive band than females, indicating a greater common rate modulation. Further evidence indicated MU pairs from the VMO and VM/VMO have 228% and 212% greater odds of having beta band oscillations than the VM, indicating control of those muscle groups has a common cortical modulation. Study 3 looked at changes in the autonomic nervous system across the menstrual cycle via heart rate variability analysis. Heart rate variability decreases from the follicular to the luteal phases of the menstrual cycle, indicating a decrease in parasympathetic control. In study 4, the time and frequency domain relationship between electrocardiogram and MU discharge timing was examined between the sexes and across the menstrual cycle. The time domain relationship indicated that both males and females have MU time lag centered between 20-25 milliseconds, with an apparent modulation of this relationship across the menstrual cycle. The findings from this series of studies indicate that there are differences between the sexes which are often modified by the menstrual cycle in females.Kinesiology and Health Educatio

The relationship between blood potassium, blood lactate, and electromyography signals related to fatigue in a progressive cycling exercise test

Local muscle fatigue may be related to potassium efflux from the muscle cell and lactate accumulation within the muscle. However, this has not been verified. The primary purpose of this investigation was to determine if there was a relationship between fatigue related changes in median power frequency (MPF) of EMG signals from the vastus lateralis and blood lactate (LAC) or potassium (K) during a progressive cycling test. This was tested in eight trained cyclists and triathletes under normal and glycogen reduced conditions to modify the LAC environment. No significant relationships were found between LAC (p>0.27) or K (p>0.16) in either condition during exercise or recovery. Though both lactate and potassium have been implicated as factors relating to neuromuscular fatigue, neither is significantly related to changes in MPF during or after progressive exercise on a cycle ergometer

Changes in Plasma Potassium During Graded Aerobic Exercise and Two Hours of Recovery

Plasma potassium increases with exercise intensity. Subjects (n=8) were monitored for changes in plasma potas-sium while exercising at progressively increasing steady-state intensities and for two hours of recovery. Plasma po-tassium was significantly increased at 100% of VO2peak compared to 20% and 40% (p<0.01). Plasma potassium at 60 and 120 minutes of recovery from exercise was significantly higher than 6 minutes post exercise (p<0.015). These results support the supposition that high-intensity exercise may lead to hyperkalemia, and also indicates that in-creases in [K + ] occur up to two hours after the cessation of exercise, a newly reported phenomenon. Although, high levels of plasma potassium are known to cause cardiac abnormalities and related events, exercise induced changes in normal healthy adults are not currently believed to have clinical implications

Maximal force and tremor changes across the menstrual cycle

PURPOSE: Sex hormones have profound effects on the nervous system in vitro and in vivo. The present study examines the effect of the menstrual cycle on maximal isometric force (MVC) and tremor during an endurance task. METHODS: Nine eumenorrheic females participated in five study visits across their menstrual cycle. In each menstrual phase, an MVC and an endurance task to failure were performed. Tremor across the endurance task was quantified as the coefficient of variation in force and was assessed in absolute time and relative percent time to task failure. RESULTS: MVC decreases 23% from ovulation to the mid luteal phase of the menstrual cycle. In absolute time, the mid luteal phase has the highest initial tremor, though the early follicular phase has substantially higher tremor than other phases after 150 s of task performance. In relative time, the mid luteal phase has the highest level of tremor throughout the endurance task. CONCLUSIONS: Both MVC and tremor during an endurance task are modified by the menstrual cycle. Performance of tasks and sports which require high force and steadiness to exhaustion may be decreased in the mid luteal phase compared to other menstrual phases

Exercise-Induced Glycogen Reduction Increases Muscle Activity

International Journal of Exercise Science 9(3): 336-346, 2016. Intramuscular glycogen stores are an important energy source during extended bouts of strenuous exercise. A substantial reduction in glycogen could influence neural muscular drive and result in a decreasing quality of exercise performance and potentially increased injury rates. The aim of this study was to examine the effect of glycogen reduction on motor drive as determined by the surface electromyogram (EMG) amplitude and median frequency during a cycling graded exercise test. Eight trained cyclists performed a discontinuous cycling graded exercise test to exhaustion under both normal and glycogen reduced conditions. EMG was collected from the vastus lateralis. Repeated measures regression models indicated that EMG amplitudes were elevated at cycling workloads higher than 196 Watts and metabolic workloads higher than 40.8 ml/kg/min, corresponding to 77% VO2max. There was no effect of increases in workload or glycogen reduction on EMG median frequency. Changes in mechanical and metabolic workload had a substantial effect on EMG amplitude (Cohen’s f2 = 0.227 and 0.247, respectively), but not median frequency (Cohen’s f2 = 0.026 and 0.033, respectively). Thus, EMG amplitude is a more effective and reliable measure to examine changes in motor drive during variable workload conditions and metabolic perturbations. The results suggest that healthy glycogen reduced humans require higher levels of muscle activity in order to attain a given mechanical and metabolic workload. This may affect the long term performance of professional and military athletes who need to be able to perform at a high level for extended periods of activity

Heart Rate Variability Spectral Parameters Across the Menstrual Cycle

Heart Rate Variability Spectral Parameters Across the Menstrual Cycle Andrew Tweedell1 (Undergraduate), Matthew Tenan1 (MA, ATC) Anthony Hackney2 (PhD, DSc, FACSM), Matthew Brothers1 (PhD), Lisa Griffin1 (PhD) 1 Neuromuscular Physiology Laboratory, Department of Kinesiology, University of Texas at Austin; 2 Applied Physiology Laboratory, Department of Exercise and Sport Science, University of North Carolina at Chapel Hill Heart rate variability (HRV) is a measure of autonomic nervous system function. Absolute low frequency (LF) and high frequency (HF) and the ratio of these components (LH/HF) are used as measures of HRV. Gonadotropin hormones may affect autonomic nervous system function; however, no difference in HRV across the menstrual cycle has been found while participants were in a supine position and breathing spontaneously. The purpose of this study was to investigate different heart rate variability power spectral components across the menstrual cycle while participants were seated and breathing spontaneously. Method: Five women volunteered for this experiment. A month prior to testing, they measured basal body temperature daily to map the timing of the menstrual cycle phases. Participants were tested once in each cycle phase. A three lead electrode arrangement recorded electrocardiographic data, sampled at 1000 Hz. A piezoelectric force transducer was placed around the participant’s chest to concurrently record breathing rate. The test consisted of a 15 minute rest period at an upright seated position. Following the rest period, 5 minutes of ECG activity was recorded while the participant remained in a seated position and breathed spontaneously. A power spectral density analysis was performed on the R-R interval variations by the fast Fourier transformation method using ECGlab. The spectrum was reduced to absolute and normalized LF, HF and LH/HF. Results: There were no significant differences in the absolute LF (p=0.7944), normalized LF (p=0.4449), absolute HF (p=0.4805), normalized HF (p=0.3994), or the LF/HF ratio (p=0.6315) across the five phases of the menstrual cycle. The breathing rate also showed no significant differences (p=0.2116). Conclusions: HRV did not change across the cycle when collected in a seated position. However, slow breathing rates (\u3c10 breaths per\u3eminute) can increase low frequency power. Participant breathing rate for this study ranged from 6.6 - 23.6 breaths per minute. It is possible that the slow breathing rates caused a false increase in LF and LF/HF ratio. While confirming previous reports of HRV changes across the menstrual cycle, follow-up research should investigate seated HRV changes across the menstrual cycle in a controlled breathing condition

Cognitive Fatigue Influences Time-On-Task during Bodyweight Resistance Training Exercise

Prior investigations have shown measurable performance impairments on continuous physical performance tasks when preceded by a cognitively fatiguing task. However, the effect of cognitive fatigue on bodyweight resistance training exercise task performance is unknown. In the current investigation 18 amateur athletes completed a full body exercise task preceded by either a cognitive fatiguing or control intervention. In a randomized repeated measure design, each participant completed the same exercise task preceded by a 52 minute cognitively fatiguing intervention (vigilance) or control intervention (video). Data collection sessions were separated by 1 week. Participants rated the fatigue intervention as being significantly more mentally demanding than the control intervention (p .05). There was no statistical difference for heart rate or metabolic expenditure as a function of fatigue intervention during exercise. Cognitively fatigued athletes have decreased time-on-task in bodyweight resistance training exercise tasks

Moving Sport and Exercise Science Forward: A Call for the Adoption of More Transparent Research Practices

The primary means for disseminating sport and exercise science research is currently through journal articles. However, not all studies, especially those with null findings, make it to formal publication. This publication bias towards positive findings may contribute to questionable research practices. Preregistration is a solution to prevent the publication of distorted evidence resulting from this system. This process asks authors to register their hypotheses and methods before data collection on a publicly available repository or by submitting a Registered Report. In the Registered Report format, authors submit a stage 1 manuscript to a participating journal that includes an introduction, methods, and any pilot data indicating the exploratory or confirmatory nature of the study. After a stage 1 peer review, the manuscript can then be offered in-principle acceptance, rejected, or sent back for revisions to improve the quality of the study. If accepted, the project is guaranteed publication, assuming the authors follow the data collection and analysis protocol. After data collection, authors re-submit a stage 2 manuscript that includes the results and discussion, and the study is evaluated on clarity and conformity with the planned analysis. In its final form, Registered Reports appear almost identical to a typical publication, but give readers confidence that the hypotheses and main analyses are less susceptible to bias from questionable research practices. From this perspective, we argue that inclusion of Registered Reports by researchers and journals will improve the transparency, replicability, and trust in sport and exercise science research. The preprint version of this work is available on Sport

Moving sport and exercise science forward: A call for the adoption of more transparent research practices

This is an accepted manuscript of an article published by Springer on 04/02/2020, available online: https://doi.org/10.1007/s40279-019-01227-1 The accepted version may differ from the final published version. For re-se please see the publisher's terms and conditions.The primary means of disseminating sport and exercise science research is currently through journal articles. However, not all studies, especially those with null findings, make it to formal publication. This publication bias towards positive findings may contribute to questionable research practices. Preregistration is a solution to prevent the publication of distorted evidence resulting from this system. This process asks authors to register their hypotheses and methods before data collection on a publicly available repository or by submitting a Registered Report. In the Registered Report format, authors submit a stage 1 manuscript to a participating journal that includes an introduction, methods, and any pilot data indicating the exploratory or confirmatory nature of the study. After a stage 1 peer review, the manuscript can then be offered in-principle acceptance, rejected, or sent back for revisions to improve the quality of the study. If accepted, the project is guaranteed publication, assuming the authors follow the data collection and analysis protocol. After data collection, authors re-submit a stage 2 manuscript that includes the results and discussion, and the study is evaluated on clarity and conformity with the planned analysis. In its final form, Registered Reports appear almost identical to a typical publication, but give readers confidence that the hypotheses and main analyses are less susceptible to bias from questionable research practices. From this perspective, we argue that inclusion of Registered Reports by researchers and journals will improve the transparency, replicability, and trust in sport and exercise science research. The preprint version of this work is available on SportRχiv: https://osf.io/preprints/sportrxiv/fxe7a/.Published versio

MCID Empirical Issues

This contains the raw data used in the manuscript entitled "All MCIDs are Wrong, but Some May be Useful" for Journal of Orthopaedic &amp; Sport Physical Therap