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. 2025 Mar 14:10:129-133.
doi: 10.1016/j.cnp.2025.03.002. eCollection 2025.

Muscle excitability testing: Age and sex dependency of normative data

Matthias Thomas Exl  1   2 , Belén Rodriguez  1 , Karl Ng  3   4 , Stella Veronica Tan  5   6 , James Howells  7 , Hugh Bostock  5 , Hatice Tankisi  8   9 , Werner J Z'Graggen  1   10
Affiliations

Muscle excitability testing: Age and sex dependency of normative data

Matthias Thomas Exl et al. Clin Neurophysiol Pract. .

Abstract

Objective: To establish normative data for muscle excitability testing in the tibialis anterior muscle of a healthy population, and to determine their dependence on age and sex.

Methods: Parameters of muscle velocity recovery cycle recordings with 1, 2 and 5 conditioning stimuli of 197 healthy subjects and frequency ramp recordings of 151 healthy subjects were retrospectively analysed for age and sex differences.

Results: There were no differences by sex and only small age differences were found in healthy subjects older than 60 years for the muscle excitability parameters muscle relative refractory period, early supernormality and latency to the first response in a train at 15 Hz and 30 Hz.

Conclusions: In this study, based on a large sample of muscle velocity recovery cycle and frequency ramp recordings, we have provided normative data and shown that muscle excitability testing is not influenced by sex, and that age only has an influence from the age of 60 years onwards on parameters reflecting muscle membrane potential.

Significance: Our results suggest that future studies no longer need to control for sex when using a healthy control group.

Keywords: Age; Direct muscle stimulation; Electric stimulation; Electromyography; Multi-fibre muscle velocity recovery cycle; Sarcolemmal excitability properties.

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Conflict of interest statement

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [Hugh Bostock and James Howells receive from UCL shares of the royalties for sales of the Qtrac software. The other authors have no potential conflicts of interest to declare.].

Figures

Fig. 1
Fig. 1
MVRC and frequency ramp. (A) Top: Mean MVRC recordings for 1, 2 and 5 conditioning stimuli, indicating the parameters MRRP (muscle relative refractory period), ESN (early supernormality) and LSN (late supernormality). Bottom: Mean differences between 2 and 1 (2–1) and between 5 and 1 (5–1) conditioning stimuli, indicating the parameters XLSN (extra late supernormality for 2) and 5XLSN (extra late supernormality for 5 conditioning stimuli).(B) Mean frequency ramp recordings, showing changes in latency for the first and last responses in a train as frequency was increased to 30 Hz.
Fig. 2
Fig. 2
Age-related changes in muscle excitability. Scatter plots illustrating age-related changes in A: muscle relative refractory period (MRRP), B: early supernormality (ESN), and C: latency to the first response in train at 15 Hz (Lat(15 Hz)first) for the age groups 21–60 (grey) and 61–77 years (black). Lines are regression lines ± SD and R values correlation coefficients.
Fig. 3
Fig. 3
MVRCs and frequency ramps in younger and older subjects. (A) Top: MVRC recordings with single conditioning stimulus in healthy subjects aged 21–60 and 71–77 years (mean ± SE). Bottom: Mean differences between 2 and 1 and between 5 and 1 conditioning stimuli (means ± SE) as in Fig. 1A. (B) Frequency ramps as in Fig. 1B, compared between ages 21–60 and 71–77 (mean ± SE).
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