THE INFLUENCE OF ATTENTIONAL FOCUS INSTRUCTION ON NEUROMUSCULAR FATIGUE DURING A SUBMAXIMAL ELBOW FLEXION CONTRACTION

A.K. Antolinez¹, E. Noel¹, I. Halperin², E.J. Lockyer¹, D.C. Button¹

¹Memorial University of Newfoundland, School of Human Kinetics and Recreation, St John's, Canada, ²Tel Aviv University, Sylvan Adams Sports Institute, Tel-Aviv, Israel

Background: Verbal cues during exercise and rehabilitation sciences are used to instruct, give feedback and cue a client during a motor execution. The method used to provide these verbal cues has been shown to impact the client's physical performance. Verbal cues often direct a client's focus of attention (FOA) toward themselves, which is defined as internal focus (IF) or externally, towards their environment, termed external focus (EF). Previous studies found that the use of external cues positively impacts performance for tasks requiring accuracy, balance, strength and endurance. However, the physiological mechanisms underlying this phenomenon have not been described yet, nor do we know the impact of FOA on physical fatigue.

Purpose: Our research study was conducted with the goal of determining if FOA influences neuromuscular fatigue of the elbow flexors and to determine potential underlying mechanisms.

Methods: Twenty healthy university students (10 females and 10 males) completed one experimental session, which included two randomized continuous submaximal isometric contractions of the dominant elbow flexors until fatigue and isometric maximal voluntary contractions (MVICs) pre- and post- the submaximal fatigue contractions while verbally receiving either EF or IF cues. Each submaximal fatigue contraction was separated by 30 minutes. The EF cue was “pull up on the clamp (over the wrist of the dominant arm),” and the IF cue was “contract your biceps brachii”. Transcranial Magnetic Stimulation and electrical stimulation of Erb’s point were used to elicit motor evoked potentials (MEP) and maximal compound muscle action potentials (Mmax) as measures of corticospinal and peripheral excitability, respectively, of the biceps brachii during the submaximal fatiguing contraction. Electromyography (EMG) of the biceps and triceps brachii was recorded during all contractions.Nine of the twenty participants returned to the laboratory and completed the same experimental session as above, but no stimulation was used during this session.

Results: There was no significant difference between IF and EF during the fatiguing submaximal contraction. Furthermore, there was no significant difference in the MEP/Mmax ratio between IF and EF. While MVC prior to fatigue was higher during EF compared to IF it was not significant.Biceps/triceps brachii EMG ratio was significantly (p=0.004) higher in IF compared to EF during the no-stimulation experiment.

Conclusions: We conclude that the FOA does not have an impact on time to fatigue nor corticospinal excitability of the biceps brachii during a continuous submaximal elbow flexion contraction to fatigue. Interestingly the biceps/triceps EMG ratio was reduced (i.e. lower co-contraction) by IF during the fatiguing contraction when stimulation was not given. These results suggest that: the effect of FOA on EMG is altered by stimulation and the change in the EMG ratio may be due to peripheral as opposed to central factors. Finally, neuromuscular efficiency may be influenced by focus type.

Implications: Many people suffer from the debilitating effects of physical fatigue and therefore have reduced performance. During rehabilitation exercise the type of verbal cues given from practitioners to clients could be one of the factors that helps mitigate fatigue induced impairments, facilitate physical performance and enhance recovery

Funding acknowledgements: This research was funded by an NSERC Discovery Grant to Dr. Duane Button.

Keywords:
Attention
Corticospinal excitability
Neurophysiology

Topics:
Musculoskeletal: upper limb
Neurology
Sport & sports injuries

Did this work require ethics approval? Yes

Institution: Memorial University of Newfoundland

Committee: Interdisciplinary Committee on Ethics in Human Research (ICEHR)

Ethics number: 20220524