Effects of an Exhaustive Exercise on Motor Skill Learning and on the Excitability of Primary Motor Cortex and Supplementary Motor Area

Abstract

We examined, on 28 healthy adult subjects, the possible correlations of an exhaustive exercise, and the consequent high blood lactate levels, on immediate (explicit) and delayed (implicit) motor execution of sequential finger movements (cognitive task). Moreover, we determined with transcranial magnetic stimulation whether changes in motor performance are associated with variations in excitability of primary motor area (M1) and supplementary motor area (SMA). We observed that, after an acute exhaustive exercise, the large increase of blood lactate is associated with a significant worsening of both explicit and implicit sequential visuomotor task paradigms, without gender differences. We also found that, at the end of the exhaustive exercise, there is a change of excitability in both M1 and SMA. In particular, the excitability of M1 was increased whereas that of SMA decreased and, also in this case, without gender differences. These results support the idea that an increase of blood lactate after an exhaustive exercise appears to have a protective effect at level of primary cortical areas (as M1), although at the expense of efficiency of adjacent cortical regions (as SMA).

FIGURE 1

Experimental design for cognitive task. When a 7-digit number stimulus appeared on a computer screen subjects had to press the keyboard keys. The 7-digit sequence of numbers was a combination of 1, 2, 3, or 4 randomly ordered and was displayed on the monitor for 2.5 s (s). Participants were instructed to press the 1, 2, 3, or 4 numbered keys as accurately and quickly as possible, with their right hand. Each key was labeled with a number representing the finger to be used: 1, 2, 3, and 4 represented the index, the middle, the ring, and the little finger, respectively. When the 7-digit number stimulus appeared, subjects had to hit the 1st number as quickly as possible and press the remaining 6 numbered keys for 2.5 s. That was defined as the explicit trial. After a 2.5 s rest, a black bar was displayed on the monitor and the participants had to press the 7-digit sequence of numbers as quickly and accurately as possible on the basis of memory for 2.5 s. That was defined as the implicit trial. It was followed by a rest for 2.5. This 2.5 s × 4 cycle was repeated 4 times. A 20 s rest followed. This entire set was repeated 5 times for a total duration of the cognitive task of 5 min.

FIGURE 2

Flowchart illustrating the principal phases of the study.

FIGURE 3

Blood lactate and blood glucose levels ( ± SD) of the 28 subjects performing the acute exhaustive exercise in 3 different days. Lactate and glucose were measured before the exercise (pre), at its conclusion (end), as well as 7 and 15 min after its conclusion. The error bars indicate standard deviation. Symbols from ANOVA with Dunns's Multiple Comparison Test: ^∗, P < 0.05; ^∗∗, P < 0.01; ^∗∗∗, P < 0.001; ^∗∗∗∗, P < 0.0001. SD = standard deviation.

FIGURE 4

Mean values ( ± SD) of response time (in milliseconds), task duration (in milliseconds), and accuracy (in percent of correct responses) of motor performance in explicit as well as implicit trials. Values were measured before (pre) and at the end (post) of the acute exhaustive exercise. SD = standard deviation.

FIGURE 5

Recruitment curves constructed from the mean amplitudes ( ± SD) of MEPs reported at the 110%, 120%, 130%, and 140% of the resting motor threshold for primary motor area and of the active motor threshold for supplementary motor area. For each cortical area curves obtained before (pre) and at the end (post) of the acute exhaustive exercise are shown. SD = standard deviation.