EMG Analysis: How Much Activity?
Question level 4: How much is the muscle active?
On this question level the EMG amplitude has to be calculated on a metric scale, giving a number to the
question “How much?” This question cannot be answered by the original microvolt scaling, because the
original electrical muscle activity is influenced by the local given detection condition which can vary greatly.
To overcome this external influence, a rescaling to percent of a certain reference value is applied - preferred
to the maximum EMG signal available in optimal static contraction condition (see The concept of MVC-
normalization).
The question: How much EMG basically ad-
dresses how much work or effort a particular
muscle needs to share in a certain exercise or
task. This kind of evaluation is important in order
to understand the effect of treatment and train-
ing exercises (Fig. 74) and reveal their character
of being low, submaximal or maximal in de-
mand: e.g. efficient strength training exercises
need a innervation level of at least 40 – 60% of
MVC to create a positive effect strength increase
due to supercompensation (muscle hypertrophy
in healthy subjects).
Ergonomics may need to understand the neuromuscular demand of a given work activity to improve tech-
niques and conditions to lower stress and strain on employees. The design of work tools, seats and other
work space related conditions/devices will benefit from the analysis of the neuromuscular effort.
Beinpresse liegend
0
10
20
30
40
50
60
70
80
90
100
EMG Aktivität [% MVC]
Flexion
Extension
Flexion
27,42 26,82 12,52 7,22 8,1 15,28 10,06 12,11
Extension
38,68 37,95 19,5 8,06 12,88 18,25 12,38 24,38
M.vast.
med.
M.vast.
lat.
M.rect.
fem.
M.semi-
tend.
M.gast.
med.
M.gast.
lat.
M. bic.
fem.
M.glut.
max.
Leg Press - Lying
EMG Activity [%MVC]
Beinpresse liegend
0
10
20
30
40
50
60
70
80
90
100
EMG Aktivität [% MVC]
Flexion
Extension
Flexion
27,42 26,82 12,52 7,22 8,1 15,28 10,06 12,11
Extension
38,68 37,95 19,5 8,06 12,88 18,25 12,38 24,38
M.vast.
med.
M.vast.
lat.
M.rect.
fem.
M.semi-
tend.
M.gast.
med.
M.gast.
lat.
M. bic.
fem.
M.glut.
max.
Leg Press - Lying
EMG Activity [%MVC]
1
1
2
3
2
3
Seat Position Seat Position Seat Position
Flexion Extension
1
1
2
3
2
3
Seat Position Seat Position Seat Position
Flexion Extension
Fig. 74: Muscular innervation profile of 8 hip/leg muscles in the horizontal squat
movement. Data shows the MVC normalized mean EMG of 6 extension and flexion
periods measured for a group of 10 subjects at 40% of the individual for one repeti-
tion maximum.
Fig. 75: EMG efficiency analysis for 3 different seat positions based on the
MVC-normalized average curve of the multifidus muscle in a sequence of back
flexion/extension cycles. At a given load (60% Max.), seat position 3 shows the
highest EMG innervation.
Fig. 76: Ergonomic EMG analysis of two shoulder muscles (upper trace -
trapezius p. desc; lower trace - deltoideus anterior) in a work task in a steel
production process. The MVC normalized signal shows the muscular de-
mand in ratio to the given video picture