| It is well known that strenuous eccentric exercise may result
in muscle damage. We proposed that vigorous eccentric exercise (EE)
would impair myoelectric activity of the biceps brachii. This study
utilised a 7-day prospective time-series design. Ten healthy males
performed a session of 70 maximal EE elbow flexion contractions. Analysis
of surface electromyography activity (sEMG) was performed on the signals
recorded during isometric contractions at 50% (IC50) and 80% (IC80)
of maximum voluntary isometric torque (MVT), deriving RMS and MDF
as sEMG parameters. Linear regression of the RMS and MDF time-series
(20-s sustained IC50 and IC80) was used to extract intercepts and
slopes of these signals on each day. Plasma creatine kinase activity
(CK), MVT, arm circumference, subjective perception of soreness and
elbow joint range of motion were also measured to assess effectiveness
of EE to evoke muscle damage. CK increased over resting values until
day 5 after EE, and remained significantly (p < 0.05) elevated
even on day 7. MVT had decreased to 45% of its initial value by day
2 after EE, and remained significantly depressed for the following
6 days. In addition, muscle soreness and arm circumference increased,
and range of motion decreased after EE. A significant shift of MDF
intercept towards lower frequencies at both IC50 and IC80 was observed
after EE in the exercised arm, and these values gradually recovered
within the next 3 days during IC50. Although there were some changes
in RMS values, these alterations were persistent in both control and
exercised arms, and did not follow a consistent pattern. In conclusion,
a prolonged reduction in MDF intercept was observed after EE, but
this was not closely time-associated with the biochemical, anthropometric
or functional markers of muscle damage. Compared to RMS, MDF was a
more consistent measure to reflect changes in sEMG.
KEY
WORDS: Eccentric
exercise, creatine kinase, surface electromyography, median frequency,
root mean square.
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