Desharnais, R., Jobin, J. & Desgagnes, P. (1995). Interaction of physical and mental stresses on heart rate and effort sense during exercise. Medicine and Science in Sports and Exercise, 27(5), Supplement abstract 355.

Young adults (N = 128) exercised at 45, 60, or 75% of VO2max. During the task, Ss were instructed to perform mathematical tasks of different difficulty levels.

It was found that effort sense (rating of perceived effort) was only affected by physical stress. Mental activity altered HR depending upon the level of exercise exertion.

• Mental activity lowered HR when the exercise intensity was low (45% of VO2max).
  
• Mental activity had no affect upon HR at moderate levels of exercise intensity (60% of VO2max).
  
• Mental activity increased HR at high levels of exercise intensity (75% of VO2max) but without Ss perceiving any change in effort sense.

Implication. Novel mental tasks during high levels of exercise intensity increase the physical cost of a performance. In competitive settings, all the mental activity required for a performance should be practiced, familiar, and without distraction. The practice of coaches giving last-minute new instructions to athletes prior to performing, is likely to detrimentally affect performances if they are attended to.

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