Fig. 1

Rationale of the experimental design, hypothesis, and summarized results. For example, if maximal voluntary contraction (MVC) strength decreased from 20.0 kg [in which a 1.0-kg weight belt (5 % of 20.0 kg) was used during the regular weight trial (Regular or Reg) for measuring ventilatory response (V. _I) before eccentric exercise (ECC) (Pre)] to 11.1 kg 2 days after ECC (D2) in experiment (Exp) 1, relative exercise intensity (weight belt/MVC strength) would increase to 9 % (1.0 kg/11.1 kg × 100) presumably with an increase in effort sense. The reason for this is that greater motor command outputs would be necessary to perform the regular weight trial because of reduced tension developments in muscle fibers damaged by ECC. Then, the relative exercise intensity would be expected to return to 5 % MVC during the subtracted weight trial (Subtracted or Sub) in which a 0.6-kg weight belt was used (5 % of 11.1 kg), and subsequently, effort sense would also be expected to return to the Pre level. In Exp 2, for instance, MVC strength is assumed to have already recovered from 11.1 to 20.0 kg. The ECC-induced increase in relative exercise intensity (9 % MVC = 1.0 kg/11.0 kg × 100) was reproduced by the added weight trial (Added or Add). In the trial, a 1.8-kg weight belt (9 % of 20 kg) would be utilized, conceivably resulting in the same level of effort sense as that in the regular weight trial at D2 without any influence from muscle damage and/or pain. As demonstrated by previous studies (e.g., [13, 14, 21]), effort sense could reflect the conscious awareness of the motor command sent to exercising muscles and effort sense and “central command” might be altered in parallel. Hence, we hypothesized that alteration in effort sense resulting from the change in relative exercise intensity caused by ECC-induced loss of muscle strength affects V. _I