inﬂammation induced by the exercise protocol. Muscle

soreness is also widely used as an indirect indicator of MD

(7,10). The soreness peak is generally observed 24–48 hours

after exercise (10) as seen in our results. Also, Nosaka and

Clarkson (27) observed that DOM S was developed 1 to 3

days after exercise, whereas C IR was largest at 4–5 days after

exercise. One cause of this phenomenon might be that the

stimuli for the sensation of muscle soreness may be the

pressure inside the muscle, but swelling itself does not

necessarily cause soreness (4,20). The signiﬁcant reduction in

DOMS 72 hours postexercise in our study, despite the other

indirect markers of MD remaining elevated, supports other

research studies suggesting that muscle soreness does not

reﬂect the magnitude of the MD induced by exercise (30,40).

However, at 24 and 48 hours postexercise DOM S peaked

and force production was at its lowest; thus, these data

suggest that DOMS may be a good indirect marker between

24 and 48 hours after exercise.

An increase in EI values has been used as an indicator of

MD after an exercise bout (15,27,31). However, to our

knowledge, this is the ﬁrst study to use the EI to analyze the

MD induced by a traditional isoinertial resistance training

session. The results showed that the EI was a sensitivity

method to measure MD induced by resistance training. The

increase in EI may be associated with an increase in the

interstitial space between ﬁbers, which results from muscle

swelling or increase in plasma enzyme levels (15). Although it

was not the main objective of the study, it is important to

note that the increase in the EI of the biceps brachii muscle

was greater than the brachialis at 24, 48, and 72 hours

(Figures 5A and B). However, there were no differences in

MT between biceps brachii and brachialis across time after

the exercise protocol. It is important to observe that MT

increased 14% in biceps brachii and only 5% in brachialis.

However, the EI difference between biceps brachii and

brachialis was only 0.2% (9.9 vs. 9.7%). These ﬁndings draw

attention to the sensitivity of the EI measurement.

Furthermore, the differences between these 2 muscles in

muscle architecture and activation may have caused this

difference in the magnitude of EI increases. Allen et al. (2)

observed that the biceps brachii has a greater activation in

relation to the brachialis during elbow ﬂexion, a fact that may

have contributed to this difference in this indirect marker of

MD. However, further studies are needed to better clarify

these differences in MD between the biceps brachii and

brachialis muscles after bouts of elbow ﬂexion. Also, an

important ﬁnding from this study is that EI at 0 hours does

not change, and MT and CIR signiﬁcantly changed at

0 hours. The increase in MT and CI R at 0 hours is mainly

related to the active hyperemia and not to the M D. Active

hyperemia is the increase in organ blood ﬂow (hyperemia)

that is associated with increased metabolic activity of

a muscle contraction. However, the increase in EI is not

related to hyperemia, rather it is likely associated with

inﬂammatory responses. Fujikake et al. (15) noted that the

increase in EI was not caused by inﬁltration of inﬂammatory

cells; however, in this same study, the authors demonstrated

that the inﬂammation responses such as edema might be

associated with increases in the EI at 24 and 48 hours. The

increase at 72 hours after the exercise might be associated

with the production of new connective tissue (27). T hus,

these results showed that EI may be a better index of M D

than MT or CIR because active hyperemia does not inﬂuence

the EI measurements (36).

Regarding the period of recovery between exercise bouts,

the results of our study conﬁrm the information that sessions

that include eccentric contractions may require a period of at

least 72 hours for muscle recovery (23). The fact that

impairments in neuromuscular function were still observed

72 hours after a protocol of conventional strength training

may have important implications in the next session of

training. Because of the temporary decrease in the ability to

produce strength, the subject may not be able to accomplish

the total volume estimated for the session, and this variable

has an important inﬂuence on neuromuscular adaptations

(23,39,40). In a longitudinal study, Ha

¨ kkinen et al. (18) found

that women who underwent training sessions 3 times a week

showed smaller increases in muscle strength than those

subjected to it twice per week. These authors explained that

the results were obtained possibly because of incomplete

muscle recovery between training sessions in the high-

frequency group. Thus, based on the ﬁndings of Ha

¨ kkinen

et al. (18) and the results of this study, women unaccustomed

to resistance training should wait at least 72 hours before

starting the next training session for the same muscle group.

A limitation of this study is that we did not control for the

subjects’ menstrual cycle. The literature suggests that estro-

gen has a protective function in the muscle cell membrane to

the damage induced by exercise (38). Thus, different stages in

the menstrual cycle may have inﬂuenced the magnitude of

damage and recovery.

In conclusion, 72 hours of recovery after a protocol of

conventional strength training was not sufﬁcient to promote

a complete recovery of elbow ﬂexor muscles of young women

unaccustomed to strength training. The results highlight the

need for adequate control of the recovery period between

sessions, especially during initial training. Also, we found that

EI, assessed by ultrasonography, is a sensitivity and reliable

measurement of MD induced by a traditional resistance

exercise protocol.

P RACTICAL A PPLICATIONS

The recovery time between resistance training sessions is one

important variable that should be controlled in periodized

training programs, and a well-planned training program

should consider complete muscular recovery before begin-

ning the next training session for the same muscle group.

Therefore, according to our results, the exercise technicians

or strength coaches should wait at least 3 days before starting

the next training session of the same muscle group during the

2582

Journal of Strength and Conditioning Research

the

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Muscle Recovery and Echo Intensity

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