Study population
Thirty-four healthy subjects were included in this study, of which 23 (67.6%) were male, and 11 (32.4%) were female. The mean ± standard deviation of subjects' age was 31.79 ± 7.23 years old.
The subjects were enrolled in the study due to certain criteria. The inclusion criteria were as follows: Men and women aged from 18 to 65 with normal general and neurological history and physical examinations, without history of any neurologic diseases (such as spinal canal stenosis, radiculopathies, etc.) and any underlying medical diseases such as diabetes, hypothyroidism, etc. Any disturbances in the examination of lower extremities, such as decreased muscle strength, reduction or absence of deep tendon reflexes, or sensory disturbances, even if the person did not have a known disease, prevented him/her from entering the study.
Exclusion criteria were intolerance of activity, premature fatigue, and neurological symptoms following activity, and the unwillingness of the patient to continue the study.
The sample size was calculated based on the formula: n = ((z1 + z2) s ^ 2)/d ^ 2 and 95% confidence interval (Z1 = 1.96) and test power factor 80% (Z2 = 0.84). The ratio of minimum means the difference of each variable that shows a significant difference (d) to the standard deviation of the change of each variable (s) equals half (d = 0.5 s), which resulted the number of at least 32 subjects. Sampling was done by convenience method.
Study procedure
This prospective semi-experimental single-group study was performed in neuromuscular clinics affiliated with the Department of Physical Medicine and Rehabilitation of Isfahan University of Medical Sciences in 2021.
At first, the study procedure was explained to the individuals, and their informed consent was obtained. A complete clinical history was then taken, and a physical examination was performed. If there were no symptoms or known diseases in the history and the examination was normal, the person was admitted to the study.
Electrodiagnostic studies were performed using an UltraPro S100 EMG/NCS/EP neurodiagnostic system (Natus Medical Incorporated). Surface self-adhesive electrodes were used to record motor and F responses. To obtain onset latency and baseline to peak amplitude, tibial nerve motor conduction studies were performed by stimulating the nerve trunk supramaximally at the ankle while recording the evoked CMAP from the abductor hallucis muscle. F waves were elicited at rest from the tibial nerve by supramaximal stimulation with a frequency of 1 Hz and 10–15 stimulations over the distal nerve and recording from the same muscle to obtain minimum, maximum, and mean latency and the difference between the maximum and minimum latency (chronodispersion) and the number of repetitions (persistence).
Acquisition conditions included a filter setting of 3 Hz to 10 kHz, a sweep speed of 8 ms per division and an amplifier gain of 0.2 millivolts per division for F waves and 5 mV for CMAP.
Following baseline studies, patients were asked to walk at normal speed for 15 min [13, 17] without interruption in the clinic environment [18, 19]. The same electrophysiological parameters were recorded immediately after and in five and ten minutes upon completion of physical activity [12, 16] (Fig. 1).
Ethical considerations
Before the project, all patients have been explained the objectives and methodology of the research and then declared informed consent. Following principles of ethics and confidentiality, all patient information remained confidential. This research was approved by Isfahan University of Medical Sciences, Iran (code of ethics: IR.MUI.MED.REC.1400.313).
Statistical analysis
Data were analyzed using the Statistical Package for Social Sciences (SPSS) software version 21 using T-test, and repeated measures ANOVA. P-value < 0.05 was considered as the significance level.