La fatica muscolare:come studiarla con l'EMG di superficie

Leonardo PianoFisioterapista OMT

Casa di Cura “La Residenza” - Rodello (CN)Studio di Fisioterapia – Alba (CN)

Arvier, 2 aprile 2016

What is fatigue?

“a transient decrease in the capacity to perform physical actions” (Enoka 2008)

“Intensive activity of muscles causes adecline 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

How to measure?

Borg scale

Rate Perceived Exertion (RPE) scale

Global Fatigue Index

Modified Fatigue Impact Scale (MS)

Fatigue Severity Scale

...

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

Surface EMG

L'elettromiografia (EMG) misura i potenziali elettrici che siformano in un muscolo durante la sua contrazione

Surface EMG

EMG

Skin preparation

IZ (Beretta-Piccoli et al 2014)

Cross-talk

Sampling rate

Amplification

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

Surface EMG and fatiguequali 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

With fatigue there is a change in the shape of action potentials (Enoka, 1994)

< amplitude

> duration

Surface EMG and fatiguequali parametri?

Result is a EMG spectrum

shift to lower frequencies(Sadoyama 1981, Winter, 1990)

Surface EMG and fatiguequali 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)