**2.3. Ramp contractions**

This protocol was had increase of maximal voluntary contraction (MVC) (10, 20 30 e 40%). The knee was flexion to 90º and isometric contractions were done by pulling on a cable fixed to the ankle which was kept at 90º relative to the longitudinal axis of the leg. The cable length was adjusted to the size of the subject's leg.

The load cell traction was performed initial with 10% MVC during 20s, immediately increased to 20% MVC during 20s. This characteristic was used until 40% of MVC.

Initially the participant with the knee flexed 90°, is a traction against the cell load corresponding to 10% maintaining that drift for 20 seconds. Immediately the participant was asked to traction 20% and so on for 30 and 40% MVC (Figure 1).

Continuous samples were collected these traction. These collections take place without the participants to rest between them. The RMS-sEMG values there is a change in load has been discarded (Figure 2).

#### **2.4. Signal processing**

The sEMG signals were amplified with gain 1000. The analog channel band pass was set to 20-500 Hz and the sampling rate for analog-to-digital conversion was 1024 Hz.

For analyses time-domain the ramp contractions, sEMG-RMS value, were calculated from a 200 millisecond (ms) window at each the following force levels: 10%, 20%, 30% e 40% of MVC.

Relationships Between Surface Electromyography and Strength During Isometric Ramp Contractions 57

Isometric exercises have shown a diversity of results regarding the strength gain and with it major changes have occurred regarding its inclusion within methods of strength training. This type of training is applied, mostly in clinics specializing in rehabilitation, physiotherapy and sports training centers aimed at improving muscle and joint injuries [8]. One of the most difficult physical qualities to be worked on is the strength, because a mistake in any application can lead to unpleasant consequences, such as stretching and muscle contractures. So the force is a physical quality that shows a vector quantity, it has magnitude and direction. The vectors are displayed graphically by a line of action, showing the direction and an attachment point of great importance for daily tasks as well as sports

In the isometric there is a consensus response to an increase in sEMG as to alter some characteristic muscle joint as the increase in signal amplitude [13,24,25,26] changes the

Classic research shown that there is not always a tendency for this linearity. Research by [31] DeLuca & Lawrence (1983) studied the electromyographic behavior of the biceps brachii, deltoid and 1st dorsal interosseous fadigantes isometric contractions. They concluded that for the interosseous muscle was an almost linear relationship, but further analysis showed a characteristic polynomial 2nd order, the same is true for the biceps and deltoid muscles that

Studies [32] Clamann & Broecker (1979) who analyzed the triceps brachii, biceps, adductor pollicis and 1st interosseous, and [33] Woods & Bigland-Ritchie (1983) who analyzed the triceps brachii, biceps, adductor pollicis and soleus, showed that the electromyographic signal amplitude as a function of force applied to the interosseous muscle and adductor pollicis was always an almost linear relationship to the muscles and biceps, triceps and soleus this relationship was not linear, unless an exception of biceps brachii this relationship

Recent research report the nonlinear characteristic between amplitude of depolarization of motor units related to time and muscle strength [11,34]. This non-linear increase was also observed in this present study (Figure 3) in isometric ramp contraction test during time performance. The data presented in a slow onset, over time it has a rapid and finally back to

According [35] Miyashita et al. (1981) and [11] Marson (2010) acting with incremental the amplitude of the electromyographic signal has an almost linear function of time to begin the individual fatigued. After the onset of muscular fatigue process the signal begins to have an

The electromyographic signal has quite often been used as a mean of assessment of muscle fatigue [17]. The increase in amplitude (Figure 3) of the EMG signal as an empirical measure

of localized muscle fatigue or as an indicator of muscle fatigue [15].

length and range of motion [27] and temperature [28,29,30].

showed a remarkable non-linearity of your data.

**3. Results and discussion** 

performance.

was almost linear [32].

grow slowly of sEMG amplitude.

increase predominantly curvilinear.

For signal processing of each isometric ramp contractions was used routine development by Matlab® and OriginLab©.

**Figure 1.** Box chart of mean,standard deviation and percentile (25,75) in 10% (F10), 20% (F20), 30%, (F30) and 40% (F40) of CVM

**Figure 2.** Relation of RMS-sEMG (µV) value versus CVM (kg). The rectangular box is the 10% (F10), 20% (F20), 30%, (F30) and 40% (F40) of CVM.
