Motor fatigue and cognitive task performance in humans

Abstract

During fatiguing submaximal contractions a constant force production can be obtained at the cost of an increasing central command intensity. Little is known about the interaction between the underlying central mechanisms driving motor behaviour and cognitive functions. To address this issue, subjects performed four tasks: an auditory choice reaction task (CRT), a CRT simultaneously with a fatiguing or a non-fatiguing submaximal muscle contraction task, and a fatiguing submaximal contraction task alone. Results showed that performance in the single-CRT condition was relatively stable. However, in the fatiguing dual-task condition, performance levels in the cognitive CRT deteriorated drastically with time-on-task. Moreover, in the fatiguing dual-task condition the rise in force variability was significantly larger than during the fatiguing submaximal contraction alone. Thus, our results indicate a mutual interaction between cognitive functions and the central mechanisms driving motor behaviour during fatigue. The precise nature of this interference, and at what level this interaction takes place is still unknown.

Figure 1. Schematic representation of experimental procedures in the two sessions

Sections 1 (practice) and 2 (control maximum voluntary contraction, cMVC, determination) have been left out for reasons of clarity. Section 3 consists of a choice reaction task (CRT) with intervening maximal voluntary contractions (MVC). In section 4 the CRT is combined with a submaximal contraction; 30 % cMVC in session 1 and 5 % cMVC in session 2. Section 5 is a repetition of section 3. In section 6 only the submaximal contraction is performed. In this illustration the frequent stimulus is 900 Hz.

Figure 2. Mean reaction times and percentage incorrect responses

Mean reaction times (± s.e.m.; A) and percentage of incorrect responses (± s.e.m.; B) in the first and second half of sections 3 (single task), 4 (dual task) and 5 (single task) for session 1 (squares; n = 16) and session 2 (circles; n = 10) are shown. Reaction times and percentage of incorrect responses are shown separately for frequent (filled symbols) and infrequent stimuli (open symbols).

Figure 3. Mean MVC force

Mean reaction times (± s.e.m.) in the first and second half of sections 3 (single task: CRT), 4 (dual task: CRT and force task), 5 (single task: CRT) and 6 (single task: force task) for session 1 (▪; n = 16) and session 2 (○; n = 10) are shown.

Figure 4. Force variation

The amount of force variation (± s.e.m.) in the first and second half of the dual-task condition (section 4) in session 1 (▪; n = 16) and session 2 (•: n = 10) and the force-alone condition (section 6; □; n = 10) are shown.