Author(s): BROWNSTEIN, C., HORNER, D., JEFFRIES, O., Institution: NEWCASTLE UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 665

INTRODUCTION:
The effect of eccentric exercise-induced muscle damage (EIMD) on cycling efficiency are unclear. While some studies report a reduction in economy during cycling with EIMD (Marcora et al. 2008), others report no change (Twist et al. 2009). This study assessed the effect of EIMD on gross and delta efficiency and the cardiopulmonary responses to cycling.
METHODS:
21 recreational athletes performed 3 × 5 minute stages of cycling at 70%, 90% and 110% of the gas exchange threshold (GET) under control conditions (Control) and 24 h following a bout of damaging eccentric exercise (Damage). Efficiency, cardiopulmonary and vastus lateralis electromyographic responses, as well as rate of perceived exertion (RPE) were assessed during the last 2 minute of each stage. Damage was assessed via changes in knee extensor maximal voluntary contraction (MVC) and potentiated twitch responses (Qtw,pot). A reliability control was also performed to assess the reliability of gross and delta efficiency, in order to assess whether any change in these measures as a result of muscle damage was beyond typical error.
RESULTS:
EIMD resulted in a reduction in MVC and Qtw,pot of ~25%. A 0.5-0.6% absolute reduction in gross efficiency across all work rates was found for Damage relative to Control (p < 0.001). However, there was no change in delta efficiency (p = 0.513). Concurrently, root-mean-squared EMG was 5-6% higher during Damage than Control, with RPE also higher for Damage (p < 0.001). Regarding the cardiopulmonary responses, an intensity-dependent increase in ventilation was found with Damage at 90% and 110%, but not 70% GET. Similarly, an increase in ventilatory equivalents for oxygen and carbon dioxide were intensity-dependent, and were only increased during Damage at 110% GET. The reliability analysis showed good to excellent reliability of gross efficiency (ICCs 0.89-0.96 across work rates), and poor reliability for delta efficiency (ICC = 0.24).
CONCLUSION:
These results demonstrate the EIMD reduces gross efficiency. The concurrently higher vastus lateralis EMG activity indicates that reductions in muscle efficiency were likely responsible, at least in part, for reductions in gross efficiency. However, delta efficiency was unchanged, which could relate to its poor reliability hindering the ability to detect change. The study also demonstrates intensity-dependent hyperventilation when cycling with EIMD, which might relate to the higher central command, as indicated by the higher EMG and RPE. These results provide new insight into the effects of EIMD on the physiological responses to cycling.

Marcora et al. (2008, Am J Physiol Regul Integr Comp Physiol)
Twist et al. (2009, Eur J Appl Physiol)