**3.3. Profile of muscular electrical activity**

The profile of the electrical activity is characterized by the length of time of muscle activity, the peak (maximum amplitude), and the time of its appearance. Changes in muscle activity can occur in any of the variables: amplitude, time, and frequency. In all three conditions muscle electrical activity was present for short periods of time.

The functions of the muscles varied through the cycle of jogging. There is no statistically significant difference between the three conditions with respect to the activity profile of the jogging cycle.

Rectus femoris, VM, and GN had a peak at the beginning of the stance phase. Tibialis anterior showed two peaks: one in the swing phase and another in the final flight. Biceps femoris and ST showed two peaks, one at the end of the non-support phase, and one in the initial support.

#### *3.3.1. Time of onset of maximum intensity*

**Table 4** gives the exact percentages of jogging cycle at which the maximum amplitude occurred. For five muscles there were no differences in the time of peak onset in their GEAV, maintaining their patterns of activity in the three conditions. As shown in Figure 3, the peak of the RF, VM, and GN appeared in the support phase; the peak of the BF, ST, TA, in the non-support phase.

In both legs, the peak appears in very similar times. Depending on the footwear, the time of occurrence of the peak is slightly modified. In general, muscles that have their peak after the impact when shod may appear a little later; and muscles that have their peak before impact when shod can occur earlier.

The peak of the RF, VM, and GN appeared between 6% and 10% in the three conditions and in both legs. The TA peaks between 94-96% in the final flight; the highest peak of the BF appeared between 88% and 90%. Semitendinosus peak appeared about 84%-90% in the shod condition, ahead respect to the barefoot condition, which appeared between 94-98%.

#### **3.4. Maximum amplitude**

The changes of amplitude or intensity of muscle activity can be evaluated considering: (1) the entire cycle, (2) the stance phase after impact, and (3) the non-support, before impact. We will describe the changes in that order.


**Table 4.** Time of occurrence (in % of the jogging cycle) of the GEAV peak in each of the three different locomotion conditions.
