Abstract High force eccentric muscle contractions canresult in delayed onset muscle soreness (DOMS), pro-longed loss of muscle strength, decreased range of mo-tion, muscle swelling and an increase of muscle proteinsin the blood. At the ultrastructural level Z-line streamingand myofibrillar disruptions have been taken as evidencefor muscle damage. In animal models of eccentric exer-cise-induced injury, disruption of the cytoskeleton andthe sarcolemma of muscle fibres occurs within the firsthour after the exercise, since a rapid loss of staining ofdesmin, a cytoskeletal protein, and the presence of fibro-nectin, a plasma and extracellular protein, are observedwithin the muscle fibres. In the present study, biopsiesfrom subjects who had performed different eccentric exercises and had developed DOMS were examined. Ouraim was to determine whether eccentric exercise leadingto DOMS causes sarcolemmal disruption and loss of des-min in humans. Our study shows that even though thesubjects had DOMS, muscle fibres had neither lost stain-ing for desmin nor contained plasma fibronectin. Thisstudy therefore does not support previous conclusionsthat there is muscle fibre degeneration and necrosis inhuman skeletal muscle after eccentric exercise leading toDOMS. Our data are in agreement with the recent find-ings that there is no inflammatory response in skeletalmuscle following eccentric exercise in humans. In com-bination, these findings should stimulate the search forother mechanisms explaining the functional and struc-tural alterations in human skeletal muscle after eccentricexercise.

Keywords Human muscle Eccentric contractions Muscle damage Desmin Fibronectin

Introduction

Delayed onset muscle soreness (DOMS), the feeling ofpain, tenderness, deep ache and stiffness that usually develops during the first 2448 h after an unaccustomedor a high intensity exercise, was described 100 years agoand was suggested to be caused by damage within themuscle (Hough 1902). Despite numerous studies there isno general consensus on the underlying mechanisms ofDOMS (Clarkson and Sayers 1999). A major causativefactor is eccentric muscle actions, i.e. active resistance to muscle lengthening, such as occurs during downhillrunning, walking downstairs or lowering a weight (Friden et al. 1981; Schwane et al. 1983; Stauber et al.1990). Such actions are characterised by a higher tensionon both the muscle fibres and the connective tissue, com-pared to concentric muscle actions (Lieber et al. 1991;Lieber and Friden 1993; Warren et al. 1993; Talbot andMorgan 1998). Manifestations of muscle damage aremyofibrillar disruption (Z-line streaming; Friden et al.1983; Friden and Lieber 1998), prolonged loss of musclestrength (Clarkson et al. 1992; Gibala et al. 1995), decre-ments in motor control (Miles et al. 1997; Pearce et al.1998; Leger and Milner 2001), changes in energy substrate levels (Evans 1991; Ferry et al. 1992) and presence of muscle proteins in the blood (Clarkson et al. 1986; Kirwan et al. 1986; Sorichter et al. 1997;MacIntyre et al. 2001). The increase in muscle proteinslike creatine kinase (CK), myoglobin and myosin heavychain fragments in the blood is most probably due to aloss of cell membrane integrity, permitting diffusion ofthe myofibre proteins into the extracellular space andsubsequently to the general circulation (Armstrong et al.1991; McNeil and Khakee 1992; Lieber and Friden1999). If an efflux of proteins from the myofibre to theblood can occur, one would also expect an influx of sub-stances from the blood into the extracellular space and

J.-G. Yu L.-E. Thornell ()Department of Integrative Medical Biology, Section for Anatomy,Ume University, 901 87 Ume, Swedene-mail: lars-eric.thornell@anatomy.umu.seTel.: +46-90-7865142, Fax: +46-90-7865480J.-G. Yu L.-E. ThornellCentre for Musculoskeletal Research, National Institute for Working Life, 907 13 Ume, SwedenC. MalmDepartment of Physiology and Pharmacology, Karolinska Institute, 114 86 Stockholm, Sweden

Histochem Cell Biol (2002) 118:2934DOI 10.1007/s00418-002-0423-1

O R I G I N A L PA P E R

Ji-Guo Yu Christer Malm Lars-Eric Thornell

Eccentric contractions leading to DOMS do not cause loss of desmin nor fibre necrosis in human muscle

Accepted: 17 May 2002 / Published online: 18 June 2002 Springer-Verlag 2002

the damaged muscle fibres (Thornell et al. 1992). In pre-vious studies we have validated that plasma fibronectinis such a substance, which can enter damaged muscle fibres and be visualised in tissue sections by immuno-histochemical methods (Thornell et al. 1992; Crenshawet al. 1993; Lieber et al. 1996).

In experimental models of muscle damage induced byeccentric exercise, the typical features reported are mus-cle fibre degeneration (Armstrong et al. 1983; Friden etal. 1983; Newham et al. 1983), muscle fibre necrosis(Nosaka and Clarkson 1996; Friden and Lieber 1998),inflammation (Jones et al. 1986; Round et al. 1987) andrepair (Ebbeling and Clarkson 1989; Clarkson and Sayers 1999). The most significant structural abnor-mality that occurs after eccentric exercise in a rabbitmodel is the selective loss of desmin (Lieber et al. 1996;Friden and Lieber 1998, 2001), the major intermediatefilament protein in muscle. Desmin is thought to act asan extrasarcomeric mechanical stabiliser of myofibrillarregularity and integrity (Small et al. 1992). In desminknockout mice, a cardiomyopathy and a muscular dys-trophy can be observed in muscles which are highly solicited, supporting the role of the cytoskeleton in main-taining muscle integrity (Thornell et al. 1997; Carlssonand Thornell 2001).

Since these models are used to define the mechanismsof DOMS, it is important that they actually reflect theevents leading to DOMS in humans. The purpose of thepresent study was to investigate whether eccentric exer-cise leading to DOMS causes loss of desmin and musclecell membrane damage with inflow of plasma fibronec-tin in humans.

Materials and methods

SubjectsAll subjects were informed about the meaning of the study and thepossible risk during the experimental procedures. Subjects wereasked to refrain from unaccustomed exercise during the experimen-tal period. All subjects signed an informed consent document con-sistent with the Declaration of Helsinki and the policy of the EthicsCommittees at Ume University or at the Karolinska Institute.

Downstairs running

Sixteen healthy male subjects with a mean age of 24.3 years(range 2130 years) participated in this study. Ten subjects tookpart in a bout of eccentric exercise whereas six served as controls.

Eccentric cycling

Thirteen healthy male subjects with a mean age of 23.9 years(range 1932 years) participated in this study.

Downhill 8 treadmill

Five male and one female subjects with a mean age of 25.8 years(range 1839 years) participated in this study.

Experimental procedures

Downstairs running

The exercise protocol performed by the subjects in the study wassimilar to that used in the study of Friden et al. (1981). Subjectswere asked to run downstairs from the 10th floor to the groundfloor and then to take the elevator back to the 10th floor and repeatthe procedure 15 times. The whole experimental procedure tookabout 4045 min. Muscle soreness was evaluated twice daily for8.5 days successively and the degree of pain was self-estimated ona 010 subject rating scale (0=no soreness and 10=very, verysore).

Eccentric bicycling

Not later than 2 days before the eccentric cycling exercise eachsubjects maximal oxygen uptake during concentric cycling wasdetermined (Medical Graphics CPX system, St Paul, Minn.,USA). A standard incremental cycling test was performed, startingat a work rate of 100 W at 60 rpm with a 50-W increase in workrate every 2 min until exhaustion. The electrically powered bicy-cle used in this study has previously been used for the eccentriccycling exercise (Friden et al. 1983). It consists of an electricalmotor, an electrical induction clutch and a modified cycle ergome-ter. Subjects were instructed to maintain 60 rpm for 30 min at awork rate equal to the highest concentric cycling work rate main-tained for 2 min during the concentric cycling VO2,max test. Allsubjects performed eccentric cycling at 250 or 300 W and the eccentric exercise can be considered maximal or close to maximalfor most subjects, with respect to eccentric muscular exercise capacity. Muscle soreness was self-estimated on the 010 ratingscale at the time points of blood and muscle sampling (before, im-mediately after and 6, 24 and 48 h, and 4 and 7 days post-exer-cise). Blood for CK analysis was drawn from an arm vein intoheparinised tubes (Becton Dickinson, France). For further detailssee Malm et al. (2000)

Downhill treadmill running

Not later than 2 days before the 45-min downhill running exercise,each subjects VO2,max was determined (AMIS 2001; Inovision,Denmark). A standard incremental running test was performed ona treadmill (Rodby Electronics, Sweden). After a 10- to 15-minwarm-up at a speed chosen by the subject and a brief resting peri-od (approximately 5 min) the test started on a treadmill with a 1slope and this was increased 1 every minute until the subjectswere exhausted. Running speed was constant and set at each sub-jects estimated 10-km racing pace. Subjects were asked not to per-form any strenuous or unaccustomed exercise for 7 days beforethe 45-min running exercise and until the muscle biopsy and lastblood sample were taken (7 days post-exercise). For further detailssee Malm (2001).

The running speed during the 45-min exercise was chosenbased on VO2 measurements from each subject when running attwo different speeds for 6090 s. These measurements were per-formed as part of the warm-up for the VO2,max test. All subjectsmanaged to run at the chosen speed for 45 min. Subjects reportedto the laboratory between 08:00 and 10:00 and were instructed toeat a light breakfast not later than 2 h before the exercise. Waterwas given ad libitum during the exercise. The 45-min running ex-ercise was preceded by a 10-min warm-up on the treadmill at 0and an individually chosen speed. Between 20 and 23 min, and 42and 45 min of exercise, VO2 and heart rate were recorded. Mea-sured exercise intensity between 42 and 45 min was at 57% (range4866%) of VO2,max and 90% (8298%) of maximum heart rate.Before, 24, 48 and 72 h, and 7 days after exercise muscle sorenesswas self-estimated on the 010 subject rating scale in the rightthigh muscles when the subjects were in a prone, dorsal positionwith the right leg lifted 5 cm from the surface. Muscle pain wasself-evaluated by placing a rubber cylinder (area=5 cm2) attached

30

to a 5-kg weight (giving a pressure of 10 N cm2) on the midsec-tion of the right vastus lateralis muscle.

Muscle biopsies

Downstairs running

Using local skin anaesthesia, open surgical biopsies from the soleus muscle were obtained from both control and exercised sub-jects. A biopsy was taken at 1 h after the exercise from four of thesubjects, whereas two biopsies were taken alternately from theright and left leg from the other six subjects at 23 days and78 days after the exercise. A control biopsy was taken from thecorresponding site on control subjects who did not perform the exercise.

Eccentric bicycling

Muscle biopsies were taken from the vastus lateralis using the for-ceps biopsy technique. In both the control and exercise group, thefirst, second, fourth and sixth biopsies were taken in the left legand the third, fifth and seventh biopsies were taken in the rightleg. The first biopsy in each leg was taken in the distal part of themuscle and each subsequent biopsy was taken approximately 2 cmproximally to the previous one. This procedure was done in orderto minimise the influence of each biopsy on the following one. After local epidermal anaesthesia (Carbocain 20 mg/ml; ASTRA,Sdertlje, Sweden) a 1.5-cm incision was made through the skinand a 50- to 100-mg muscle sample was removed.

Downhill treadmill running

Muscle biopsies were taken from the left vastus lateralis 48 h afterexercise using the same procedure as in the eccentric cycling protocol.

Histology, histochemistry and immunohistochemistry

The muscle biopsies were mounted in embedding medium (Tissue-Tek OCT; Miles, Elkkhart, Ill., USA), frozen in propane chilledwith liquid N2 (160C) and stored at 80C until used. Serialtransverse and longitudinal sections (58 m thick) were cut at25C on a Reichert Jung cryostat (Leica, Nussloch, Germany) andcollected on glass slides. Cross-sections were stained with haema-toxylin-eosin and a modified Gomori trichrome stain for basic his-topathology (Dubowitz 1985). Myofibrillar adenosine triphospha-tase (ATPase) histochemical analysis performed after preincuba-tions at pH 4.3, 4.6 and 10.4 revealed muscle fibre types (Dubowitz1985). Transverse and longitudinal sections were immunostainedwith primary antibodies against plasma fibronectin and desmin.The sections were washed in 0.01 M phosphate-buffered saline(PBS) and immersed in 5% normal serum (Dako, Glostrup, Den-mark). Excess serum was wiped off and sections were incubatedwith primary antibodies against human plasma fibronectin (number341635; Calbiochem, La Jolla, Calif., USA) and desmin (monoclo-nal antibody desmin D33 and polyclonal antibody desmin A611;Dako, Carpinteria, Calif., USA). The antibodies were diluted in0.01 M PBS containing 0.1% bovine serum albumin and used attheir optimal dilution. Visualisation of antibodies was performedwith indirect fluorescence, using fluorescein isothiocyanate- or Alexa-conjugated secondary antibodies (Dako or Jackson Immuno-research Laboratory, West Grove, Pa., USA), or with the indirectperoxidaseanti-peroxidase technique (Beesley et al. 1993). Con-trol sections were treated as above, except that the primary anti-body was exchanged with non-immune serum. Sections for all biopsies were observed with a Nikon (eclipse, E800; Japan) micro-scope and photographed with a Spot camera (RT colour, DiagnosticInstruments, USA) connected to Adobe Photoshop (Adobe Sys-tems, USA).

Results

All exercise protocols used resulted in DOMS in all sub-jects and serum CK activity was significantly increasedwhen measured.

Downstairs running

All subjects felt a strong discomfort upon contractionand palpation of the soleus muscle with a mean maximalself-estimated value of 7.8 (SD 1.4) at 48 h post-exer-cise.

Eccentric cycling

Mean maximal soreness was 6.0 (SD 1.5) 48 h after theexercise. The highest peaks of CK in the serum were observed at 6 h [166.4 U/l (SD 171.8 U/l)] and 24 h[155.0 U/l (SD 124.3 U/l)] post-exercise.

Downhill running

Mean maximal soreness was 5.2 (SD 3.0) 48 h after theexercise. Muscle pain was estimated to a mean value of5.3 (SD 2.0) 48 h after exercise. Creatine kinase in serum was elevated maximally to 936 U/l (SD 146 U/l)24 h post-exercise.

Muscle biopsies

All biopsies, both taken before and after the exercise,showed fibres in well-ordered fascicles. In the controlsand in most biopsies taken after exercise, the fibres seenin cross-sections were tightly packed and had a polygo-nal shape. In some post-exercise biopsies the space be-tween fibres was enlarged and the fibres were moreround. No evidence of muscle fibre degeneration, hya-line fibres or infiltration of mononuclear cells was ob-served in sections stained using routine histologicalstaining (Fig. 1A). In sections stained with anti-plasmafibronectin, strong staining was seen in endothelial cellsof the capillaries and a somewhat weaker staining wasobserved between the muscle fibres (Figs. 1B, 2A). In noinstance did the muscle fibres contain plasma fibronec-tin. All muscle fibres were stained in sections treatedwith the antibodies against desmin (Figs. 1C, 2B). Atlow magnification, we observed a striated pattern ofstaining covering all the muscle fibres (Fig. 1C) or a homogenous staining within the fibres (Fig. 2B). Thisdifference reflects the thickness of the sections and thelimited resolution at low magnification. In some biop-sies, an obvious difference in the degree of desmin stain-ing between fibres was seen within the same section(Fig. 1C). By comparing these sections with adjacent

31

serial sections stained for myofibrillar ATPase activity, itwas evident that the different degree of staining observedcorrelated to different muscle fibre types (not shown).The type I fibres generally had a weaker staining intensi-ty than type II fibres with anti-desmin staining (Fig. 1C).

When the sections were examined at a higher magni-fication, the desmin staining sometimes formed an irregular network or highly stained dots (Fig. 3A). Similarly, in longitudinal sections studied at a highermagnification, many irregularities such as variability inspacing between the striations, focally increased stainingand longitudinal strands of staining were apparent(Fig. 3BD).

Discussion

Because plasma fibronectin staining was never observedwithin the muscle fibres, we conclude that the muscle fibre plasma membrane had become neither permeablefor fibronectin nor appreciably disrupted as a conse-quence of the three types of eccentric exercise leading toDOMS. In previous studies on cardiomyocytes we haveshown that plasma fibronectin is an excellent marker forplasmalemmal damage (Thornell et al. 1992; Holmbom1997). The presence of plasma fibronectin inside a car-diomyocyte shows that the cell has become irreversiblydamaged. Similarly, we have previously shown that plas-ma fibronectin is an excellent and reliable marker fordamaged skeletal muscle fibres after long-distance run-ning (Crenshaw et al. 1993) as well as in biopsies of different muscle diseases known to cause muscle fibrenecrosis, such as polymyositis and muscular dystrophy(Thornell, unpublished observations). In biopsies taken1 day after an exhausting ultramarathon race, the Western State 100 mile (160 km) Run, we observed that1% of the 3,698 fibres analysed contained plasma fibro-nectin (Crenshaw et al. 1993). The same fibres lackedstaining for phosphorylase, a soluble enzyme, had noplasma membranes, were infiltrated with macrophagesand were thus considered necrotic. In that study we

32

Fig. 1 Three serial transverse sections from a soleus muscle biopsy taken 3 days after downstairs running and stained with hae-matoxylin-eosin (A), anti-human plasma fibronectin (B) and anti-desmin (C). No necrotic fibres are seen in A. No fibres contain fibronectin in B and no fibres lack desmin staining in C. Bar20 m

Fig. 2 Serial longitudinal sections of a soleus muscle biopsy taken1 h after downstairs running and stained with anti-human plasmafibronectin (A) and anti-desmin (B). No staining for fibronectin isseen inside the fibres (A) and no major disturbance in the stainingfor desmin is seen (B). Bar 20 m

showed that fibronectin staining is a better marker thanincreased technetium uptake to reveal muscle necrosis.In animal experiments involving muscle lengtheningcontractions we have also used plasma fibronectin as amarker for necrotic fibres (Lieber et al. 1996; Friden andLieber 1998, 2001). Thus, the absence of fibronectinstaining inside muscle fibres in the three different set-tings of eccentric exercise leading to DOMS reportedhere clearly indicates that sarcolemmal disruption of amagnitude that leads to muscle fibre degeneration is nota feature of human skeletal muscles affected by musclesoreness.

However, the muscle fibres in our subjects were un-doubtedly affected since strong pain was felt upon con-traction, there was a leakage of CK into the blood andthe myofibrils and the desmin cytoskeleton were altered.In the desmin cytoskeleton we observed irregularities inthe spacing of cross-striations, the appearance of longitu-dinal strands and variability in the level of staining inten-sity. This is in accordance with our previous publicationon muscle soreness (Friden et al. 1984), but clearly dif-fers from the desmin pattern seen in eccentric muscle in-jury in rabbits (Lieber et al. 1996; Friden and Lieber1998; Lieber and Friden 1999). In ongoing studies weare examining in detail how the cytoskeleton is affectedin human muscle fibres subjected to eccentric exerciseand preliminary results suggest that the changes seen inthe desmin cytoskeleton are mainly due to an increasedsynthesis of desmin and remodelling of the myofibrilsrather than degeneration (Yu and Thornell 2001). On thebasis of the findings presented here we conclude that thesequence of events proposed to lead to muscle damage ina rabbit model (Lieber et al. 1996; Lieber and Friden1999; Friden and Lieber 2001) does not apply to thepathogenesis of muscle soreness in human muscle.

33

Fig. 3AD Sections of a vastus lateralis muscle biopsy taken 48 hafter treadmill running (8 decline) and stained with anti-desmin.At higher magnification changes from the normal desmin patternwere seen in both transverse (A) and longitudinal sections (BD).In A the desmin-stained network is somewhat irregular and somehighly stained dots are seen (arrows). In longitudinal sections(BD) the cross-striations vary in spacing and in degree of staining.Longitudinal strands were often apparent (arrows in C and D). Bar 10 m

Acknowledgements We wish to thank Mrs. M. Enerstedt for ex-cellent technical assistance, F. Pedrosa-Domellof and G. Butler-Browne for helpful comment on the manuscript. This work wassupported by grants from the Swedish National Centre for Re-search in Sports, the Swedish Medical Research Council (03934)and the Medical Faculty, Ume University.

References

Armstrong RB, Ogilvie RW, Schwane JA (1983) Eccentric exercise-induced injury to rat skeletal muscle. J Appl Physiol 54:8093

Armstrong RB, Warren GL, Warren JA (1991) Mechanisms of exercise-induced muscle fibre injury. Sports Med 12:184207

Beesley JE, Rickwood D, Hames B (1993) Immunocytochemistry:the prectical approach series. Eynsham, IRL Press, Oxford

Carlsson L, Thornell LE (2001) Desmin-related myopathies inmice and man. Acta Physiol Scand 171:341348

Clarkson PM, Sayers SP (1999) Etiology of exercise-inducedmuscle damage. Can J Appl Physiol 24:234248

Clarkson PM, Byrnes WC, McCormick KM, Turcotte LP,White JS (1986) Muscle soreness and serum creatine kinaseactivity following isometric, eccentric, and concentric exer-cise. Int J Sports Med 7:152155

Clarkson PM, Nosaka K, Braun B (1992) Muscle function afterexercise-induced muscle damage and rapid adaptation. MedSci Sports Exerc 24:512520

Crenshaw AG, Friden J, Hargens AR, Lang GH, Thornell LE(1993) Increased technetium uptake is not equivalent to mus-cle necrosis: scintigraphic, morphological and intramuscularpressure analyses of sore muscles after exercise. Acta PhysiolScand 148:187198

Dubowitz V (1985) Muscle biopsy: a practical approach. Bailliere,Tindall, London

Ebbeling CB, Clarkson PM (1989) Exercise-induced muscle damage and adaptation. Sports Med 7:207234

Evans WJ (1991) Muscle damage: nutritional considerations. IntJ Sport Nutr 1:214224

Ferry A, Amiridis I, Rieu M (1992) Glycogen depletion and resyn-thesis in the rat after downhill running. Eur J Appl Physiol64:3235

Friden J, Lieber RL (1998) Segmental muscle fibre lesions afterrepetitive eccentric contractions. Cell Tissue Res 293:165171

Friden J, Lieber RL (2001) Eccentric exercise-induced injuries tocontractile and cytoskeletal muscle fibre components. ActaPhysiol Scand 171:321326

Friden J, Sjostrom M, Ekblom B (1981) A morphological study ofdelayed muscle soreness. Experientia 37:506507

Friden J, Sjostrom M, Ekblom B (1983) Myofibrillar damage following intense eccentric exercise in man. Int J Sports Med4:170176

Friden J, Kjrell U, Thornell LE (1984) Delayed muscle sorenessand cytoskeletal alterations: an immunocytological study inman. Int J Sports Med 5:1518

Gibala MJ, MacDougall JD, Tarnopolsky MA, Stauber WT, Elorriaga A (1995) Changes in human skeletal muscle ultra-structure and force production after acute resistance exercise.J Appl Physiol 78:702708

Holmbom B (1997) Plasma fibronectin as a morphological markerof irreversible cardiomyocyte injury. Ume University medicaldissertations, Ume

Hough T (1902) Ergographic studies in muscular soreness. AmJ Physiol 7:7692

Jones DA, Newham DJ, Round JM, Tolfree SE (1986) Experimen-tal human muscle damage: morphological changes in relationto other indices of damage. J Physiol 375:435448

Kirwan JP, Clarkson PM, Graves JE, Litchfield PL, Byrnes WC(1986) Levels of serum creatine kinase and myoglobin inwomen after two isometric exercise conditions. Eur J ApplPhysiol 55:330333

Leger AB, Milner TE (2001) Muscle function at the wrist after eccentric exercise. Med Sci Sports Exerc 33:612620

Lieber RL, Friden J (1993) Muscle damage is not a function ofmuscle force but active muscle strain. J Appl Physiol 74:520526

Lieber RL, Friden J (1999) Mechanisms of muscle injury after eccentric contraction. J Sci Med Sport 2:253265

Lieber RL, Woodburn TM, Friden J (1991) Muscle damage in-duced by eccentric contractions of 25% strain. J Appl Physiol70:24982507

Lieber RL, Thornell LE, Friden J (1996) Muscle cytoskeletal dis-ruption occurs within the first 15 min of cyclic eccentric con-traction. J Appl Physiol 80:278284

MacIntyre DL, Sorichter S, Mair J, Berg A, McKenzie DC (2001)Markers of inflammation and myofibrillar proteins followingeccentric exercise in humans. Eur J Appl Physiol 84:180186

Malm C (2001) Immunological changes in human blood and skel-etal muscle in response to physical exercise. Karolinska Uni-versity dissertations, Stockholm

Malm C, Nyberg P, Engstrom M, Sjodin B, Lenkei R, Ekblom B,Lundberg I (2000) Immunological changes in human skeletalmuscle and blood after eccentric exercise and multiple biop-sies. J Physiol 529:243262

McNeil PL, Khakee R (1992) Disruptions of muscle fibre plasmamembranes. Role in exercise-induced damage. Am J Pathol140:10971109

Miles MP, Ives JC, Vincent KR (1997) Neuromuscular control following maximal eccentric exercise. Eur J Appl Physiol76:368374

Newham DJ, McPhail G, Mills KR, Edwards RH (1983) Ultra-structural changes after concentric and eccentric contractionsof human muscle. J Neurol Sci 61:109122

Nosaka K, Clarkson PM (1996) Changes in indicators of inflam-mation after eccentric exercise of the elbow flexors. Med SciSports Exerc 28:953961

Pearce AJ, Sacco P, Byrnes ML, Thickbroom GW, Mastaglia FL(1998) The effects of eccentric exercise on neuromuscularfunction of the biceps brachii. J Sci Med Sport 1:236244

Round JM, Jones DA, Cambridge G (1987) Cellular infiltrates inhuman skeletal muscle: exercise induced damage as a modelfor inflammatory muscle disease? J Neurol Sci 82:111

Schwane JA, Johnson SR, Vandenakker CB, Armstrong RB(1983) Delayed-onset muscular soreness and plasma CPK andLDH activities after downhill running. Med Sci Sports Exerc15:5156

Small JV, Furst DO, Thornell LE (1992) The cytoskeletal lattice ofmuscle cells. Eur J Biochem 208:559572

Sorichter S, Mair J, Koller A, Gebert W, Rama D, Calzolari C,Artner-Dworzak E, Puschendorf B (1997) Skeletal troponin Ias a marker of exercise-induced muscle damage. J ApplPhysiol 83:10761082

Stauber WT, Clarkson PM, Fritz VK, Evans WJ (1990) Extracel-lular matrix disruption and pain after eccentric muscle action.J Appl Physiol 69:868874

Talbot JA, Morgan DL (1998) The effects of stretch parameters oneccentric exercise-induced damage to toad skeletal muscle.J Muscle Res Cell Motil 19:237245

Thornell LE, Holmbom B, Eriksson A, Reiz S, Marklund S, Naslund U (1992) Enzyme and immunohistochemical assess-ment of myocardial damage after ischaemia and reperfusion ina closed-chest pig model. Histochemistry 98:341353

Thornell LE, Carlsson L, Li Z, Mericskay M, Paulin D (1997)Null mutation in the desmin gene gives rise to a cardiomyopa-thy. J Mol Cell Cardiol 29:21072124

Warren GL, Hayes DA, Lowe DA, Armstrong RB (1993) Mechan-ical factors in the initiation of eccentric contraction-inducedinjury in rat soleus muscle. J Physiol 464:457475

Yu JG, Thornell LE (2001) The cytoskeleton is not primarily affected upon delayed muscle soreness. Med Sci Sports Exerc33(suppl S41)

34