Am J Physiol Regulatory Integrative Comp Physiol
281: R155–R161, 2001.
Lengthening contractions are not required to induce
protection from contraction-induced muscle injury
TIMOTHY J. KOH AND SUSAN V. BROOKS
Institute of Gerontology, University of Michigan, Ann Arbor, Michigan 48109–2007
Received 9 January 2001; accepted in final form 12 March 2001
mouse extensor digitorum longus; fiber degeneration; force
deficit; isometric training; passive stretch training
CONTRACTION-INDUCED SKELETAL
muscle injury is associated with stretch of highly activated muscle (lengthening contractions; 1, 19, 23, 37). Fortunately, training
with lengthening contractions protects muscle from
injury during subsequent lengthening contractions (7,
13, 24, 26, 33–35). Despite the consensus for the existence of exercise-induced protection from muscle injury
and its potential importance, little is known about this
phenomenon.
Armstrong and colleagues (1, 35) proposed that a
population of injury susceptible fibers undergoes necrosis following lengthening contractions. Training with
lengthening contractions may eliminate susceptible fibers, or parts of fibers, leaving muscle fibers that are
less susceptible to injury. In addition, Devor and
Address for reprint requests and other correspondence: S. V.
Brooks, Institute of Gerontology, Univ. of Michigan, Ann Arbor, MI
48109–2007 (E-mail: [email protected]).
http://www.ajpregu.org
Faulkner (9) reported that muscles injected with bupivacaine to induce degeneration or regeneration
showed dramatic protection from contraction-induced
injury. This observation is consistent with the hypothesis that degeneration or regeneration is sufficient to
protect muscle from contraction-induced injury.
Whether degeneration or regeneration is necessary to
induce protection has not been established.
There is little evidence of whether training that does
not involve lengthening contractions nor measurable
injury can protect muscle from lengthening contraction-induced injury. A single bout of training with
maximal voluntary isometric contractions protected
muscle from enzyme leakage during a subsequent
identical bout of isometric exercise (6). Whether maximal isometric training can protect muscle from injury
following lengthening contractions is not known. Previous exposure to level running that did not appear to
produce injury in vastus intermedius and triceps
brachii muscles protected these muscles from injury
during downhill running in rats (35). Although the
authors speculated that the lengthening contractions
during level running produced the protective effect,
isolating the effects of a specific type of contraction
using the treadmill running model is not possible.
The hypothesis of this study was that lengthening
contractions and subsequent muscle fiber degeneration
and/or regeneration are required to induce exerciseassociated protection from lengthening contraction-induced muscle injury. A corollary to this hypothesis was
that training with isometric contractions or stretches
of passive muscle that did not produce fiber degeneration and/or regeneration would not induce protection.
MATERIALS AND METHODS
Animals. Three- to-four-month-old specific pathogen-free
male C57BL/6 mice (Harlan Sprague-Dawley, Indianapolis,
IN) were housed in a pathogen-free barrier facility until
experimentation and then returned to a separate barrier
facility between experimental procedures. All experimental
procedures were approved by the University Committee for
the Use and Care of Animals at the University of Michigan.
In situ pretraining evaluation. Each mouse was anesthetized with an intraperitoneal injection of 2% avertin (0.015
ml/g body wt). Supplemental doses (0.1 ml) were adminisThe costs of publication of this article were defrayed in part by the
payment of page charges. The article must therefore be hereby
marked ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734
solely to indicate this fact.
0363-6119/01 $5.00 Copyright © 2001 the American Physiological Society
R155
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016
Koh, Timothy J., and Susan V. Brooks. Lengthening
contractions are not required to induce protection from contraction-induced muscle injury. Am J Physiol Regulatory
Integrative Comp Physiol 281: R155–R161, 2001.—We tested
the hypothesis that lengthening contractions and subsequent
muscle fiber degeneration and/or regeneration are required
to induce exercise-associated protection from lengthening
contraction-induced muscle injury. Extensor digitorum longus muscles in anesthetized mice were exposed in situ to
repeated lengthening contractions, isometric contractions, or
passive stretches. Three days after lengthening contractions,
maximum isometric force production was decreased by 55%,
and muscle cross sections contained a significant percentage
(18%) of injured fibers. Neither isometric contractions nor
passive stretches induced a deficit in maximum isometric
force or a significant number of injured fibers at 3 days. Two
weeks after an initial bout of lengthening contractions, a
second identical bout produced a force deficit (19%) and a
percentage of injured fibers (5%) that was smaller than those
for the initial bout. Isometric contractions and passive
stretches also provided protection from lengthening contraction-induced injury 2 wk later (force deficits ⫽ 35 and 36%,
percentage of injured fibers ⫽ 12 and 10%, respectively),
although the protection was less than that provided by
lengthening contractions. These data indicate that lengthening contractions and fiber degeneration and/or regeneration
are not required to induce protection from lengthening contraction-induced injury.
R156
PROTECTING SKELETAL MUSCLE FROM INJURY
decrease in maximum isometric force produced 10 min and 3
days following the training bout expressed as a percentage of
pretraining values.
Posttraining injury bout and functional evaluation. Two or
six weeks after the training bout of lengthening contractions,
passive stretches, or isometric contractions, EDL muscles
were exposed in situ to 75 lengthening contractions using a
protocol identical to the training bout of lengthening contractions. Three days after the posttraining injury bout, mice
were anesthetized, isometric contractile properties were
measured in situ using a protocol identical to that for the
pretraining evaluation, and force deficits were calculated in
the same manner as those for the training bout.
Histological evaluation. After the final in situ functional
evaluations, anesthetized mice were killed by cervical dislocation. EDL muscles were dissected, blotted dry, weighed,
mounted in tissue freezing media, and frozen in isopentane
chilled with dry ice. Cross sections were cut at 10 ␮m with a
cryostat and stained with hematoxylin and eosin. Fibers
exhibiting clear evidence of degeneration or regeneration and
the total number of fibers in a single cross section from the
mid-belly of each muscle were counted with the aid of a
microscope imaging system (Bioquant, Nashville, TN). Degenerating fibers were defined as those with infiltration of
inflammatory cells, pale and/or discontinuous staining of the
cytoplasm, or a substantially swollen appearance. Regenerating fibers were defined as those with nonperipheral nuclei
without other degenerative changes. Fiber counts were performed by two independent observers, and values were averaged. Degenerating and regenerating fibers are reported as a
percentage of the total number of fibers in the cross section.
Data analysis. Physiological cross-sectional area (PCSA)
was calculated by dividing muscle mass by the product of Lf
and muscle density, 1.06 mg/mm3. Specific Po was calculated
by dividing Po by physiological cross-sectional area. Mean
values and standard errors were determined for each variable for each group. Force deficits and percentages of injured
fibers were compared between groups using the nonparametric Kruskal-Wallis one-way ANOVA on ranks (multiple
groups) or the Mann-Whitney ranked-sum test (two groups).
The 0.05 level was taken to indicate statistical significance. A
significantly smaller force deficit in trained vs. nontrained
muscle indicated protection from functional injury, and a
significantly smaller percentage of injured fibers indicated
protection from structural injury.
RESULTS
For 51 mice included in the study, mean body mass
(27.3 ⫾ 0.4 g) and noninjured EDL muscle mass
(10.2 ⫾ 0.1 mg), Lo (12.6 ⫾ 0.1 mm), Po (379 ⫾ 7 mN),
and specific Po (22.7 ⫾ 0.3 N/cm2) were similar to those
reported previously for mice of the same strain and age
(4). Ten minutes after the training protocols, lengthening contractions resulted in a force deficit of 59.0 ⫾
6.1%, passive stretches resulted in a much smaller
force deficit of 9.8 ⫾ 1.4%, and isometric contractions
resulted in a force deficit not significantly different
from zero. The absence of a force deficit after isometric
contractions suggests that the force deficit associated
with lengthening contractions was not due to surgical
procedures or to metabolic fatigue. The force deficits
measured 10 min after the training protocols involving
stretch of active or passive muscle may have been
influenced by a shift in Lo to longer muscle lengths (15),
because Po was measured at the Lo determined before
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016
tered if the mouse responded to a toe pinch. A small incision
was made at the right ankle, and the distal tendons of the
extensor digitorum longus (EDL) muscle were exposed. The
mouse was then placed on a heated platform maintained at
37°C. The hindlimb was stabilized by fixing the distal femur
between sharpened screws and securing the foot with tape to
the platform. The intact tendon was tied with 4–0 silk to the
lever arm of a servomotor (Aurora Scientific, Richmond Hill,
ON, Canada), which controlled the length of the muscle and
measured the force developed by the muscle. The servomotor
was controlled by a computer to move the lever arm through
a given distance at a constant velocity. The computer was
also used to collect and analyze force data. The small region
of exposed tendon was kept moist with warmed isotonic
saline.
The EDL muscle was activated via the peroneal nerve
using an isolated stimulator (Grass Instruments, West Warwick, RI), and needle electrodes were placed transcutaneously adjacent to the nerve. A pulse duration of 0.2 ms was
used for all contractions. Stimulation voltage was set at 6 V
and adjusted in 1-V increments until maximal twitch tension
was achieved, and a voltage 1.2 times this value was used for
the remainder of the experiment (⬃8–12 V). Muscle length
was set to the length of the EDL with the knee fully extended
and the foot fully plantarflexed and then adjusted in
0.125-mm increments for maximal twitch tension. Stimulation frequency was set to 200 Hz and then adjusted in 50-Hz
increments for maximum isometric force (typically 250 Hz).
Finally, optimal muscle length (Lo) was determined for maximum isometric force (Po); this was either the same as, or
slightly shorter than, the optimum length for twitch contractions. Lo was measured using well-defined anatomical landmarks as previously established (4). Optimal muscle fiber
length (Lf) was calculated by multiplying Lo by the Lf-to-Lo
ratio of 0.44 (23). This evaluation protocol minimized the
number of isometric contractions performed to minimize the
possible confounding influence on subsequent training and
injury protocols.
Training bout and functional evaluation. The EDL muscle
was exposed to one of three training protocols: stretches with
the muscle near maximally activated (lengthening contractions), stretches with the muscle relaxed (passive stretches),
or near-maximal activation of the muscle held at Lo (isometric contractions). Near-maximal activation was achieved using the voltage determined in In situ pretraining evaluation
to elicit a maximal response and a frequency (150 Hz) that
elicited 94 ⫾ 1% Po. A sham training group underwent
identical surgical procedures, but no stretch or contractions
were performed. All training protocols involved 75 repetitions performed at 0.25 Hz for a total exercise duration of 5
min. Lengthening contractions and passive stretches were
initiated at Lo and were of 20% strain relative to Lf, at a
velocity of 1 Lf/s. For lengthening contractions, stretch was
initiated 100 ms after the beginning of stimulation from the
plateau of force development. Ten minutes after the 75 repetitions, Po was remeasured. The incision at the ankle was
closed with 7–0 nylon and bathed with povidone-iodine solution, and then mice were allowed to recover from anesthesia.
For some mice in each group, mice were anesthetized 3 days
after the training bout and isometric contractile properties
were measured in situ using a protocol identical to that for
the pretraining evaluation. These mice were then killed by
cervical dislocation immediately after functional testing, and
EDL muscles were removed for histological evaluation (see
Histological evaluation). These mice provided data for nontrained muscle that could be compared with those for trained
muscle. Force deficits were calculated for each mouse as the
PROTECTING SKELETAL MUSCLE FROM INJURY
Fig. 1. A: force deficits and percentages of injured fibers in cross
sections of extensor digitorum longus (EDL) muscles 3 days after
bouts of 75 passive stretches (n ⫽ 6), isometric contractions (n ⫽ 6),
or lengthening contractions (n ⫽ 8). Force deficit calculated as
percent decrease in maximum isometric force produced before and
after bout. Percentage of injured fibers calculated as percentage of
the total number of fibers in a cross section determined to exhibit
clear signs of degeneration. Values are means with SE bars. * Significant difference from zero; ** significant difference from control
(P ⬍ 0.05). B: cross sections of EDL muscles stained with hematoxylin and eosin 3 days after no exercise, passive stretches, isometric
contractions, and lengthening contractions. Note substantial change
in morphology of muscle following lengthening contractions and
enlarged blood vessel (v) in muscle following passive stretch. A
muscle spindle is also present (s).
DISCUSSION
The major finding of this study was that neither
lengthening contractions nor muscle fiber degeneration and/or regeneration was necessary to induce
exercise-associated protection from lengthening contraction-induced injury. Training with isometric contractions and passive stretch protected muscle from
injury, as evaluated by the force deficit at 3 days for
both training protocols and by the percentage of injured fibers at 3 days for the passive stretch protocol.
That the isometric contraction or passive stretch pro-
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016
the protocol for both the pre- and 10 min posttraining
evaluations. The force deficits at 3 days were not influenced by any shift in Lo, because Lo was determined
anew at the beginning of the evaluation at 3 days, and
Po was measured at this newly determined Lo. In fact,
3 days after training with lengthening contractions, Lo
was 12.9 ⫾ 0.1 mm, ⬃2% greater than before training.
Two weeks after training, however, Lo was not different from the pretraining value.
Three days after the training protocol, lengthening
contractions resulted in a force deficit of 55.1 ⫾ 5.0%,
whereas passive stretches and isometric contractions
resulted in force deficits not different from zero (Fig.
1A). Compared with cross sections from nonexercised
control EDL muscles, cross sections from EDL muscles
3 days after lengthening contractions contained a
greater percentage of injured fibers (0.8 ⫾ 0.2 vs.
18.3 ⫾ 2.9%; Fig. 1A). Passive stretches and isometric
contractions produced percentages of injured fibers not
different from control. Some muscles that had undergone training with passive stretches did show some
evidence of enlarged blood vessels and edema between
muscle fibers (Fig. 1B). There were very few (⬍0.3%)
regenerating fibers in any of these groups.
Two weeks after the training bout of lengthening
contractions, muscles had fully recovered force production as values for Po were not different from preinjury
values (the force deficit, 5.2 ⫾ 4.3%, was not significantly different from zero). The second bout of lengthening contractions performed 2 wk after the training
bout produced a force deficit and a percentage of injured fibers at 3 days that was only one-third of values
for untrained muscles (Fig. 2). Six weeks after the
training bout, the second bout of lengthening contractions produced a force deficit and a percentage of injured fibers at 3 days that were not different from
values for untrained muscle (Fig. 2). The percentages
of regenerating fibers 2 and 6 wk after the initial bout
were 15.1 ⫾ 5.2 and 8.0 ⫾ 1.7%, respectively.
Two weeks after the training bouts of either isometric contractions or passive stretches, the bout of lengthening contractions produced a force deficit at 3 days
that was two-thirds of the values for untrained muscles
(Fig. 3). For muscles trained with passive stretches,
the percentage of injured fibers at 3 days was one-half
of that for untrained muscles (Fig. 3). For muscles
trained with isometric contractions, the percentage of
injured fibers at 3 days was not significantly different
from values for untrained muscle (Fig. 3). There was a
significantly greater percentage of injured fibers and a
trend of a larger force deficit (P ⫽ 0.06), for muscles
trained with passive stretches or isometric contractions compared with those trained with lengthening
contractions. The percentage of regenerating fibers
was very small 2 wk after either passive or isometric
training (⬍0.3%). Two weeks after sham training, a
bout of lengthening contractions produced a force deficit (54.7 ⫾ 7.5%) and a percentage of injured fibers
(18.1 ⫾ 3.1%) at 3 days that was not different from
those for untrained muscle, suggesting that the surgical procedures did not induce protection from injury.
R157
R158
PROTECTING SKELETAL MUSCLE FROM INJURY
that some damage may have occurred, perhaps to blood
vessels or to connective tissue. Whether such potential
damage or resulting edema plays a role in inducing
protection is a question for future investigation. Although training with isometric contractions or passive
stretches provided protection, training with lengthening contractions tended to provide greater protection.
Lengthening contractions or degeneration and regeneration may thus produce stronger stimuli for protection than isometric contractions or passive stretches.
tocols did not produce muscle fiber degeneration and/or
regeneration is supported by three sets of observations.
First, there was no significant percentage of injured
fibers in muscle cross sections 3 days after the protocols. Second, there was also no significant force deficit
at 3 days. Third, there was no significant percentage of
regenerating fibers in muscle cross sections 2 wk after
these protocols. Cross sections of some muscles subjected to passive stretches did show evidence of enlarged blood vessels and edema at 3 days, suggesting
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016
Fig. 2. A: force deficits and percentages of injured fibers in cross
sections of EDL muscles 3 days after an injury bout of 75 lengthening
contractions in groups that were not trained (n ⫽ 8), 2 wk posttraining (n ⫽ 7), or 6 wk posttraining (n ⫽ 7), with an identical bout of
lengthening contractions. Force deficit calculated as percent decrease in maximum isometric force produced before and after bout.
Percentage of injured fibers calculated as percentage of total number
of fibers in a cross section determined to exhibit clear signs of
degeneration. Values are means with SE bars. Force deficits and
percentages of injured fibers for all groups were significantly greater
than zero (P ⬍ 0.05). * Significant difference from nontrained group
(P ⬍ 0.05). B: cross sections of EDL muscles stained with hematoxylin and eosin 3 days after an injury bout of 75 lengthening contractions for mice that were not trained, 2 wk posttraining, or 6 wk
posttraining with an identical bout of lengthening contractions.
Section representing nontrained group is same as that used for
lengthening contraction group of Fig. 1.
Fig. 3. A: force deficits and percentages of injured fibers for EDL
muscles 3 days after an injury bout of 75 lengthening contractions in
groups that were not trained (n ⫽ 8), 2 wk posttraining with passive
stretches (n ⫽ 7), or 2 wk posttraining with isometric contractions
(n ⫽ 10). Force deficit calculated as percent decrease in maximum
isometric force produced before and after bout. Percentage of injured
fibers calculated as percentage of total number of fibers in a cross
section determined to exhibit clear signs of degeneration. Values are
means with SE bars. Force deficits and percentages of injured fibers
for all groups were significantly greater than zero (P ⬍ 0.05). * Significant difference from nontrained group (P ⬍ 0.05). B: cross sections from EDL muscles stained with hematoxylin and eosin 3 days
after an injury bout of 75 lengthening contractions for mice that were
not trained, 2 wk posttraining with passive stretches, or 2 wk
posttraining with isometric contractions. Section representing nontrained group is same as that used for lengthening contraction group
of Fig. 1.
PROTECTING SKELETAL MUSCLE FROM INJURY
force-length relationship for each group, and any potential increase in sarcomere number in this study
would not account for the protection observed.
Injury after lengthening contractions takes place in
two stages: a primary insult directly associated with
the contractions and delayed, secondary damage that
peaks ⬃3 days after the exercise (12, 18, 26). The
primary injury appears to be mechanical in nature (2,
5, 40), perhaps a result of inhomogeneities in the
strengths of sarcomeres in series, resulting in strong
sarcomeres pulling weak sarcomeres apart (21, 25, 28).
A potential mechanism for exercise-induced protection
from the primary injury is increasing the strength of
the cytoskeletal protein network that surrounds sarcomeres (39) and transmits tension through the membrane (30, 38). Upregulation of proteins in this network
(e.g., desmin, talin, vinculin, dystrophin) could help to
stabilize sarcomeres during lengthening contractions
and thus protect muscle fibers from injury. For example, lengthening contractions resulted in increased
talin and vinculin concentration in rat soleus muscles
(14). Talin and vinculin are also upregulated, along
with utrophin, another cytoskeletal protein, in regenerated muscle of mdx mice (17). Whether upregulation
of these proteins is directly involved in protecting muscle from contraction-induced injury has yet to be determined.
The secondary injury may be related to the inflammatory response and free radical damage (10, 36).
Following lengthening contractions, inflammatory cell
invasion has been associated with increased reactive
oxygen species generation (3) and increased oxidation
of glutathione (22). A potential mechanism for protecting muscle from the secondary injury is upregulation of
free radical scavenging pathways. Administration of
exogenous superoxide dismutase reduced the force deficit and percentage of injured fibers following lengthening contractions in the EDL muscles of young and
old mice (43), suggesting that superoxide or its byproducts contribute to the injury process. Although 12 wk of
high intensity level treadmill running increased both
superoxide dismutase and glutathione peroxidase activity in rat soleus muscles (8), regulation of antioxidant activity following lengthening contractions or
passive stretches has not been explored.
Parts of the initial and delayed force deficits may be
a result of mechanically induced or free-radical-induced damage to the excitation-coupling apparatus
and resulting failure (29, 41). Thus exercise-induced
protection from lengthening contraction-induced force
deficit may be partly due to protection from excitationcoupling failure (24). Whether training protects muscle
from excitation-coupling failure remains to be determined.
In conclusion, we found that neither lengthening
contractions nor muscle fiber degeneration and/or regeneration were necessary to induce exercise-associated protection from lengthening contraction-induced
injury. However, lengthening contractions and associated degeneration or regeneration did produce greater
protection than training with passive stretch or iso-
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016
A previous study reported that in vivo endurance
isometric training (10 Hz stimulation, 1 s on/1 s off
duty cycle, 30 min/day, 5 days/wk, 3 wk) did not protect
rabbit dorsiflexor muscles from lengthening contraction-induced injury as evaluated by the force deficit
(31). Comparing these previous results with those from
the present study suggests that isometric exercise
involving relatively small forces may not provide a
sufficient stimulus to induce protection; high force isometric contractions may be necessary. Further investigation is required to determine whether there is a
force threshold at which isometric contractions will
provide protection from lengthening contraction-induced injury.
The magnitude and time course of protection induced by lengthening contractions are in agreement
with those reported previously for the mouse tibialis
anterior muscle (34). In the present study, the protective effect of a bout of lengthening contractions, indicated by the reduction of the force deficit by two-thirds,
was evident at 2 wk but not detected at 6 wk. Sacco and
Jones (34) reported that a bout of 120 in vivo lengthening contractions produced a force deficit of 48%
(measured in vitro) 3 days after the bout. Three weeks
after the initial bout, a second bout of lengthening
contractions produced a force deficit of only 20% 3 days
after the second bout. By 12 wk, a second bout produced a force deficit at 3 days not significantly different
from that for the initial bout. Whether the protective
effect of the initial bout was lost earlier than 12 wk was
not determined in the previous study. The magnitude
of protection induced by lengthening contractions in
the present study was also consistent with that produced by bupivacaine injection (9), suggesting that
degeneration or regeneration may induce similar protective mechanisms in the two models.
One proposed mechanism of exercise-induced protection from the primary injury is an increase in the
number of sarcomeres in series in muscle fibers (20,
42). Downhill run training has been reported to increase sarcomere number in the rat vastus intermedius muscle (20). An increase in sarcomere number
would 1) decrease sarcomere extension for a given
muscle lengthening and 2) shorten sarcomere length
for any given muscle length and thus move sarcomeres
away from the descending limb of the force-length
relationship. Morgan (25) has argued that the descending limb is inherently unstable and that because of this
instability, muscle is particularly susceptible to injury
when lengthening contractions are performed at long
lengths (e.g., 27). However, experiments using training
with controlled lengthening contractions have revealed
no significant increase in sarcomere number in rabbit
dorsiflexor muscles (16) or in rat EDL muscles (Brooks,
unpublished data). In the present study, there was no
significant increase in Lo 2 wk after any of our training
protocols. In addition, for the injury protocol, lengthening contractions were initiated at Lo, and stretch
parameters were scaled to Lo (magnitude, velocity).
Consequently, lengthening contractions were likely
performed over approximately the same portion of the
R159
R160
PROTECTING SKELETAL MUSCLE FROM INJURY
metric contractions. The mechanisms underlying the
protection provided by passive stretch and isometric
training, and those associated with the greater protection induced by lengthening contractions, await further investigation.
Perspectives
The authors thank Drs. John Faulkner and Dennis Claflin for
helpful discussions on the project. We also thank Rob Crawford for
expert advice on histology and Jessica Mayne for help with data
collection.
Financial support was provided by National Institute on Aging
Grants AG-06157 and AG-00114.
REFERENCES
1. Armstrong RB, Ogilvie RW, and Schwane JA. Eccentric
exercise-induced injury to rat skeletal muscle. J Appl Physiol 54:
80–93, 1983.
2. Armstrong RB, Warren GL, and Warren JA. Mechanisms of
exercise-induced muscle fiber injury. Sports Med 12: 184–207,
1991.
3. Best TM, Fiebig R, Corr DT, Brickson S, and Ji L. Free
radical activity, antioxidant enzyme, and glutathione changes
with muscle stretch injury in rabbits. J Appl Physiol 87: 74–82,
1999.
4. Brooks SV and Faulkner JA. Contraction-induced injury:
recovery of skeletal muscles in young and old mice. Am J Physiol
Cell Physiol 258: C436–C442, 1990.
5. Brooks SV, Zerba E, and Faulkner JA. Injury to muscle
fibers after single stretches of passive and maximally activated
muscles in mice. J Physiol (Lond) 488: 459–469, 1995.
6. Clarkson PM, Litchfield P, Graves J, Kirwan J, and
Byrnes WC. Serum creatine kinase activity following forearm
flexion isometric exercise. Eur J Appl Physiol 53: 368–371, 1985.
7. Clarkson PM and Tremblay I. Exercise-induced muscle damage, repair, and adaptation in humans. J Appl Physiol 65: 1–6,
1988.
8. Criswell D, Powers S, Dodd S, Lawler J, Edwards W,
Renshler K, and Grinton S. High intensity training-induced
changes in skeletal muscle antioxidant enzyme activity. Med Sci
Sports Exerc 25: 1135–1140, 1992.
9. Devor ST and Faulkner JA. Regeneration of new fibers in
muscle of old rats reduces contraction-induced injury. J Appl
Physiol 87: 750–756, 1999.
10. Evans WJ and Cannon JG. The metabolic effects of exerciseinduced muscle damage. Exerc Sport Sci Rev 19: 99–125, 1991.
11. Faulkner JA, Brooks SV, and Zerba E. Muscle atrophy and
weakness with aging: contraction-induced injury as an underlying mechanism. J Gerontol 50A: 124–129, 1995.
12. Faulkner JA, Jones DA, and Round JM. Injury to skeletal
muscles of mice by forced lengthening during contractions. Q J
Exp Physiol 74: 661–670, 1989.
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016
Our finding that training with isometric contractions
or passive stretches protects muscle from lengthening
contraction-induced injury has therapeutic implications. Contraction-induced injury is associated with
pain and weakness in young, healthy individuals (10)
and loss of mobility in the elderly (11) and may be
associated with the muscle wasting and death in children with Duchenne muscular dystrophy (32). Further
study is warranted to determine whether training can
protect aged or dystrophic muscle from injury. Training with isometric contractions or passive stretches
may be particularly appropriate for preventing injury
in elderly or dystrophic individuals, who may not recover well from training involving lengthening contractions.
13. Faulkner JA, Opiteck JA, and Brooks SV. Injury to skeletal
muscle during altitude training: induction and prevention. Int
J Sports Med 13: S160–S162, 1992.
14. Frenette J and Cote CH. Modulation of structural protein
content at the myotendinous junction following eccentric contractions. Int J Sports Med 21: 313–320, 2000.
15. Jones C, Allen T, Talbot J, Morgan DL, and Proske U.
Changes in the mechanical properties of human and amphibian
muscle after eccentric exercise. Eur J Appl Physiol 76: 21–31,
1997.
16. Koh TJ and Herzog W. Eccentric training does not increase
sarcomere number in rabbit dorsiflexor muscles. J Biomech 31:
499–501, 1998.
17. Law DJ, Allen DL, and Tidball JG. Talin, vinculin and DRP
(utrophin) concentrations are increased at mdx myotendinous
junctions following onset of necrosis. J Cell Sci 107: 1477–1483,
1994.
18. Lieber RL, Schmitz MC, Mishra DK, and Friden J. Contractile and cellular remodeling in rabbit skeletal muscle after cyclic
eccentric contractions. J Appl Physiol 77: 1926–1934, 1994.
19. Lieber RL, Woodburn TM, and Friden J. Muscle damage
induced by eccentric contractions of 25% strain. J Appl Physiol
70: 2498–2507, 1991.
20. Lynn R and Morgan DL. Decline running produces more
sarcomeres in rat vastus intermedius muscle fibers than incline
running. J Appl Physiol 79: 831–838, 1994.
21. Macpherson PCD, Dennis RG, and Faulkner JA. Sarcomere
dynamics and contraction-induced injury to maximally activated
single muscle fibres from soleus muscles of rats. J Physiol (Lond)
500: 523–533, 1997.
22. McArdle A, van der Meulen JH, Catapano M, Symons
MCR, Faulkner JA, and Jackson MJ. Free radical activity
following contraction-induced injury to the extensor digitorum
longus muscles of rats. Free Radic Biol Med 26: 1085–1091,
1999.
23. McCully KK and Faulkner JA. Injury to skeletal muscle fibers
of mice following lengthening contractions. J Appl Physiol 59:
119–126, 1985.
24. McHugh MP, Connolly DAJ, Eston RG, and Gleim GW.
Exercise-induced muscle damage and potential mechanisms for
the repeated bout effect. Sports Med 27: 157–170, 1999.
25. Morgan DL. New insights into the behavior of muscle during
active lengthening. Biophys J 57: 209–221, 1990.
26. Newham DJ, Jones DA, and Clarkson PM. Repeated highforce eccentric exercise: effects on muscle pain and damage.
J Appl Physiol 63: 1381–1386, 1987.
27. Newham DJ, Jones DA, Ghosh G, and Aurora P. Muscle
fatigue and pain after eccentric contractions at long and short
length. Clin Sci (Colch) 74: 553–557, 1988.
28. Newham DJ, McPhail G, Mills KR, and Edwards RHT.
Ultrastructural changes after concentric and eccentric contractions of human muscle. J Neurol Sci 61: 109–122, 1983.
29. Newham DJ, Mills KR, Quigley BM, and Edwards RHT.
Pain and fatigue after concentric and eccentric contractions. Clin
Sci (Colch) 64: 55–62, 1983.
30. Pardo JV, D’Angelo Siliciano J, and Craig SW. A vinculincontaining cortical lattice in skeletal muscle: transverse lattice
elements (“costameres”) mark sites of attachment between myofibrils and sarcolemma. Proc Natl Acad Sci USA 80: 1008–1012,
1983.
31. Patel TJ, Cuizon D, Mathieu-Costello O, Friden J, and
Lieber RL. Increased oxidative capacity does not protect skeletal muscle fibers from eccentric contraction-induced injury.
Am J Physiol Regulatory Integrative Comp Physiol 274: R1300–
R1308, 1998.
32. Petrof BJ. The molecular basis of activity-induced muscle injury in Duchenne muscular dystrophy. Mol Cell Biochem 179:
111–123, 1998.
33. Pizza FX, Davis BH, Henrickson SD, Mitchell JB, Pace JF,
Bigelow N, DiLauro P, and Naglieri T. Adaptation to eccentric exercise: effect on CD64 and CD11b/CD18 expression. J Appl
Physiol 80: 47–55, 1996.
PROTECTING SKELETAL MUSCLE FROM INJURY
34. Sacco P and Jones DA. The protective effect of damaging
eccentric exercise against repeated bouts of exercise in the
mouse tibialis anterior. Exp Physiol 77: 757–760, 1992.
35. Schwane JA and Armstrong RB. Effect of training on skeletal
muscle injury from downhill running in rats. J Appl Physiol 55:
969–975, 1983.
36. Smith LL. Acute inflammation: the underlying mechanism in
delayed onset muscle soreness? Med Sci Sports Exerc 23: 542–
551, 1991.
37. Stauber WT, Fritz VK, Vogelbach DW, and Dahlmann B.
Characterization of muscles injured by forced lengthening. I.
Cellular infiltrates. Med Sci Sports Exerc 20: 345–353, 1988.
38. Tidball JG. Myotendinous junction injury in relation to junction
structure and molecular composition. Exerc Sport Sci Rev 19:
419–445, 1991.
39. Wang K and Ramirez-Mitchell R. A network of transverse
and longitudinal intermediate filaments is associated with sar-
40.
41.
42.
43.
R161
comeres of adult vertebrate skeletal muscle. J Cell Biol 96:
562–570, 1983.
Warren GL, Hayes DA, Lowe DA, and Armstrong RB.
Mechanical factors in the initiation of eccentric contractioninduced injury in rat soleus muscle. J Physiol (Lond) 464: 457–
475, 1993.
Warren GL, Lowe DA, Hayes DA, Karwoski CJ, Prior BM,
and Armstrong RB. Excitation failure in eccentric contractioninduced injury of mouse soleus muscle. J Physiol (Lond) 468:
487–499, 1993.
Whitehead NP, Allen TJ, Morgan DL, and Proske U. Damage to human muscle from eccentric exercise after training with
concentric exercise. J Physiol (Lond) 512: 615–620.
Zerba E, Komorowski TE, and Faulkner JA. Free radical
injury to skeletal muscles of young, adult, and old mice. Am J
Physiol Cell Physiol 258: C429–C435, 1990.
Downloaded from http://ajpregu.physiology.org/ by 10.220.32.246 on November 7, 2016