This document discusses using surface electromyography (EMG) to study muscle fatigue. It defines fatigue as a decline in muscle performance and force capacity. Surface EMG can objectively evaluate muscle performance and fatigue by measuring changes in electrical activity during muscle contraction. As muscles fatigue, the shape of motor unit action potentials changes, resulting in lower frequencies in the EMG signal spectrum. Specific time and frequency domain parameters like mean and median frequency can serve as indices of fatigue by detecting this spectral shift to lower frequencies. Surface EMG provides an objective way to measure muscle fatigue beyond subjective scales.

1. La fatica muscolare:
come studiarla con l'EMG di superficie
Leonardo Piano
Fisioterapista OMT
Casa di Cura “La Residenza” - Rodello (CN)
Studio di Fisioterapia – Alba (CN)
Arvier, 2 aprile 2016

2. What is fatigue?
“a transient decrease in the capacity to
perform physical actions” (Enoka 2008)
“Intensive activity of muscles causes a
decline in performance, known as
fatigue…” (Allen & Westerblad, 2001)
... can refer to a motor deficit, a perception or a decline in mental function, it can describe the
gradual decrease in the force capacity of muscle or the endpoint of a sustained activity, and it can
be measured as a reduction in muscle force,
or an exhaustion of contractile function (Enoka 2008)
a change in electromyographic activity

3. How to measure?
 Borg scale
 Rate Perceived Exertion (RPE) scale
 Global Fatigue Index
 Modified Fatigue Impact Scale (MS)
 Fatigue Severity Scale
 ...

4. Why EMG?
 To objective the evaluation of muscle performance
 To improve the clinical and subjective assessment
 To manage the rehabilitation program after trauma or
surgery (es.: ACL reconstruction)
 To correctly manage the rest period during training
sessions
 For research

5. Surface EMG
L'elettromiografia (EMG) misura i potenziali elettrici che si
formano in un muscolo durante la sua contrazione

6. Surface EMG

7. EMG
 Skin preparation
 IZ (Beretta-Piccoli et al 2014)
 Cross-talk
 Sampling rate
 Amplification

9. EMG and muscle fibers
Biological signal frequency:
10 - 450 Hz
Slow twitch motor units (tonic - Type I)
Frequency range = (20) 70 - 125 Hz
Fast twitch motor units (phasic - Type II)
Frequency range = 126 - 250 Hz

10. Surface EMG and fatigue
quali parametri?
Frequency-domain parameters
Mean Frequency (MNF)
Median Frequency (MDF)
Time-domain parameters
Average Rectified Value (ARV)
Root Mean Square (RMS)
- number of active MUAP
- Firing rate MUAP
- MUAP shape

11. With fatigue there is a
change in the shape of
action potentials
(Enoka, 1994)
< amplitude
> duration
Surface EMG and fatigue
quali parametri?
Result is a EMG spectrum
shift to lower frequencies
(Sadoyama 1981, Winter, 1990)

12. Surface EMG and fatigue
quali parametri?
Firing rate = frequency
No. of cycles (firings) per unit of time
Mean Power Frequency (MNF)
Median Power Frequency (MDF)
a decrease in the mean/median power frequency serves as an
index of fatigue (Gonzalez-Izal 2012)
Velocità di conduzione delle fibre muscolari?
(Rainoldi et al 2015)