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Muscle damage and repeated bout effect induced by enhanced-eccentric squat exercise

December 2015
The Journal of sports medicine and physical fitness 56(12)

Authors:

Giuseppe Coratella

Università degli Studi di MIlano

Federico Schena

University of Verona

Aim: Muscle damage and repeated bout effect have been studied after pure eccentric-only exercise. The aim of this study was to evaluate muscle damage and repeated bout effect induced by enhanced-eccentric squat exercise using flywheel device. Methods: Thirteen healthy males volunteered for this study. Creatine-kinase blood activity (CK), quadriceps isometric peak torque and muscle soreness were used as markers of muscle damage. The dependent parameters were measured at baseline, immediately after and each day up to 96 hours after the exercise session. The intervention consisted of 100 repetitions of enhanced-eccentric squat exercise using flywheel device. The same protocol was repeated after 4 weeks. Results: After the first bout, CK and muscle soreness were significantly greater (p<0.05) than baseline respectively up to 72 and 96 hours. Isometric peak torque was significantly lower (p<0.05) up to 72 hours. After the second bout, CK showed no significant increase (p>0.05), while isometric peak torque and muscle soreness returned to values similar to baseline after respectively 48 and 72 hours. All muscle damage markers were significantly lower after second compared to first bout. Conclusion: The enhanced-eccentric exercise induced symptoms of muscle damage up to 96 hours. However, it provided muscle protection after the second bout, performed four weeks later. Although it was not eccentric-only exercise, the enhancement of eccentric phase provided muscle protection.

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1540 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS December 2016

Anno: 2016

Mese: December

Volume: 56

No: 12

Rivista: The Journal of Sports Medicine and Physical Fitness

Cod Rivista: J Sports Med Phys Fitness

Lavoro:

titolo breve: MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS

primo autore: CORATELLA

pagine: 1540-6

citazione: J Sports Med Phys Fitness 2016;56:1540-6

er strength recovery, lower muscle soreness and lower

CK blood activity have been measured after the second

eccentric-only exercise.7 It is well established that the

rst eccentric-only exercise bout protects muscle from

muscle damage due to subsequent exercise sessions.8

Such protection has been named “repeated bout effect”.

It has been shown to last up to six months, during which

participants were not involved in any form of resis-

tance exercise.9 Even if the mechanisms underlying the

repeated bout effect have not been totally claried, in-

ammatory, neural or muscular explanations have been

proposed, as previously reviewed.10

It is well known that unaccustomed eccentric-only

exercise induces symptoms of muscle damage.1-3

Exercise-induced muscle damage can be monitored us-

ing both invasive (e.g., biopsy) and non-invasive mea-

surements. Indirect markers have been proposed and

are nowadays largely used in literature for evaluating

the muscle damage. Increases in creatine-kinase blood

activity (CK),4 muscle soreness 5 and strength loss 6 are

some of indirect muscle damage markers mainly used

in literature.

After a second eccentric-only exercise bout, the

markers of muscle damage dramatically decrease. Fast-

ORIGINAL ARTICLE

EPIDEMIOLOGY AND CLINICAL MEDICINE

Muscle damage and repeated bout effect

induced by enhanced eccentric squats

Giuseppe CORATELLA *, Alessandro CHEMELLO, Federico SCHENA

Department of Neurological and Movement Sciences, University of Verona, Verona, Italy

*Corresponding author: Giuseppe Coratella, Department of Neurological and Movement Sciences, via Casorati 43, 37131, Verona, Italy.

E-mail: giuseppe.coratella@univr.it

ABSTRACT

BACKGROUND: Muscle damage and repeated bout effect have been studied after pure eccentric-only exercise. The aim of this study was to

evaluate muscle damage and repeated bout effect induced by enhanced eccentric squat exercise using ywheel device.

METHODS: Thirteen healthy males volunteered for this study. Creatine kinase blood activity (CK), quadriceps isometric peak torque and mus-

cle soreness were used as markers of muscle damage. The dependent parameters were measured at baseline, immediately after and each day up

to 96 hours after the exercise session. The intervention consisted of 100 repetitions of enhanced eccentric squat exercise using ywheel device.

The same protocol was repeated after 4 weeks.

RESULTS: After the rst bout, CK and muscle soreness were signicantly greater (P<0.05) than baseline respectively up to 72 and 96 hours.

Isometric peak torque was signicantly lower (P<0.05) up to 72 hours. After the second bout, CK showed no signicant increase (P>0.05), while

isometric peak torque and muscle soreness returned to values similar to baseline after respectively 48 and 72 hours. All muscle damage markers

were signicantly lower after second compared to rst bout.

CONCLUSIONS: The enhanced eccentric exercise induced symptoms of muscle damage up to 96 hours. However, it provided muscle protec-

tion after the second bout, performed four weeks later. Although it was not eccentric-only exercise, the enhancement of eccentric phase provided

muscle protection.

(Cite this article as: Coratella G, Chemello A, Schena F. Muscle damage and repeated bout effect induced by enhanced eccentric squats. J Sports Med

Phys Fitness 2016;56:1540-6)

Key words: Torque - Creatine kinase - Myalgia - Isometric contraction - Muscle strength.

The Journal of Sports Medicine and Physical Fitness 2016 December;56(12):1540-6

Online version at http://www.minervamedica.it

MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS CORATELLA

Vol. 56 - No. 12 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 1541

Lavoro:

titolo breve: MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS

primo autore: CORATELLA

pagine: 1540-6

citazione: J Sports Med Phys Fitness 2016;56:1540-6

to off-season period. Each participant performed testing

measurements at the same time, in order to avoid cir-

cadian parameters variations. Participants familiarized

with both exercise and testing devices one day apart that

preceded the rst bout.

In order to investigate muscle damage induced by

enhanced eccentric squat, muscle strength and soreness

have been measured on quadriceps muscle. Although

squat exercise involves several lower limb muscles,

quadriceps has been used to estimate the effects of squat

exercise.19 In addition, greater quadriceps activation

was found while squatting with ywheel device than

conventional barbell squat.16

Participants

Thirteen healthy physically active young males,

recruited among sport science students (mean age

21.7±3.1 years; mean weight 78.2±4.4 kg; mean height

1.80±0.2 m) were involved for this study. Knee, hip or

ankle pains in the previous year were used as exclusion

criteria, as well as any practice in regular resistance ex-

ercise in the previous six months. All subjects signed a

written informed consensus and this study was previ-

ously approved by Ethical Committee of University of

Verona. Finally, this study met the ethical standards of

the journal.

Markers of muscle damage

Biochemical marker

Creatine kinase (CK) blood activity was measured us-

ing capillary blood. Blood was collected in single 32 μL

lithium heparin single use capillary pipette (Reotron®

PST, La Roche, Basel, Switzerland) after pricking a n-

ger with a sterile single-use lancing device (Accucheck,

La Roche). Heparinized blood was pipetted to the test

strip (Reotron® CK, La Roche) immediately after col-

lection and then inserted in the device optical reader

(Reotron® Plus, La Roche). Test strips were stored in a

refrigerator at +4°C and the optical reader was checked

daily according manufacturer’s instructions.

isometric peak torque

Participants performed peak torque measurements on

isokinetic dynamometer (Cybex, Lumex, Ronkokoma,

The previous studies that investigated the exercise-

induced muscle damage and the repeated bout effect

have used isokinetic 11 or dynamic constant external re-

sistance 12, 13 eccentric-only exercises. Tesch et al. devel-

oped a ywheel device (YoYo® Technology, Stockholm,

Sweden), in which concentric phase is weight-free and

eccentric phase is enhanced by the inertia accumulated

during the concentric phase.15 Due to its gravity inde-

pendence, it was originally designed for counteracting

muscle atrophy and osteoporosis in spacemen involved

in space ights.15 However, further subsequent studies

showed the effectiveness of enhanced eccentric train-

ing for inducing muscle strength and structure adapta-

tions.16, 17

Recently, one study investigated muscle damage sub-

sequent to enhanced eccentric a supine-squat exercise

session.18 However, in such study, only biochemical

markers have been measured. In addition, the authors

did not investigate the repeated bout effect. Therefore,

the aim of the present study is to evaluate the exercise-

induced muscle damage and the repeated bout effect

following an enhanced eccentric squat exercise using a

ywheel ergometer.

Materials and methods

This study was divided in two separate sessions and

testing assessments. For investigating muscle damage,

participants were tested at baseline, immediately after,

and once a day up 96 hours after the exercise bout, for

a total of 6 measurements (Figure 1). Then, to examine

the magnitude of the repeated bout effect, the same pro-

tocol was repeated after 4 weeks. The length of the inter-

val between the two bouts was selected according to the

literature.14 During such 4 weeks, the participants were

strictly required to avoid any strenuous physical activ-

ity involving lower limbs. In order to get greater adher-

ence to such instruction, these 4 weeks corresponded

Figure 1.—The procedures for muscle damage evaluation are shown.

The entire protocol was repeated after 4 weeks.

Eccentric exercise

Baseline Immediately after 24 hrs 48 hrs 72 hrs 96 hrs

CORATELLA MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS

1542 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS December 2016

Statistical analysis

Sphericity assumption was analyzed used Mauchly’s

W test. Normality was analyzed using Shapiro-Wilk test.

Dependent parameters changes were analyzed by two–

way repeated measure ANOVA (time × bout) performed

using SPSS v.20.0 (SPSS Inc., IBM Corp., Armonk, NY,

USA). Post-hoc analysis using Bonferroni’s correction

was then calculated to investigate factors time (6 levels)

and bout (2 levels). Difference in average power between

rst vs second bout were analyzed using a pair-wise t-

test. Signicance was set at P<0.05. Data are shown as

mean ± SD. Post-hoc differences are shown using effect

size (ES) and condence intervals (95% CI). Accord-

ing the Cohen’s standard, an ES=0.3 was considered as

small, ES=0.5 as medium and ES=0.8 as large.

Results

Average power

No difference in average power resulted comparing

rst vs. second bout in concentric (respectively 248±83

and 275±92 W, P=0.536) and eccentric phases (respec-

tively 462±121 and 498±137 W, P=0.741).

CK blood activity

The time-course of the CK blood activity values is

shown in gure 2. No signicant time x bout interac-

tion (P=0.646) was found for the CK blood activity.

As a within-bout comparison, after the rst bout, com-

pared to baseline, CK blood activity was signicantly

higher after 24 (ES=1.1, 95% CI: 0.3-1.9, P=0.006),

48 (ES=1.1, 95% CI: 0.1-2.0, P=0.003) and 72 hours

(ES=0.9, 95% CI: 0.2-1.7, P=0.020) (Figure 2). Com-

pared to baseline, after the second exercise bout, CK

blood activity did not result in different values up to

96 hours (Figure 2). As a between-bouts comparison,

Compared to the rst bout, after the second bout, CK

blood activity was signicantly lower after 48 (ES=0.6,

95% CI: 0.1-1.1, P=0.018) and 72 hours (ES=0.6, 95%

CI: 0.0-1.1, P=0.034) (Figure 2).

Isometric peak torque

The time course of isometric peak torque values is

shown in Figure 3. A signicant time × bout interaction

NY, USA). The device was calibrated and gravity cor-

rection executed according manufacturer procedures.

Subjects were seated on dynamometer, with trunk,

shoulders and tested knee secured by belts. Knee was

properly aligned to the center of rotation. A lever im-

mobilized the untested limb. Isometric peak torque was

investigated at 60° of knee joint exion, considering 0°

as full knee extension. Participants received standard-

ized encouragements by operator to maximally perform

the test. Three repetitions were performed and the peak

torque was inserted in data analysis. Only the dominant

limb was tested.

muscle soreness

A visual analogic scale was assessed to detect sore-

ness during quadriceps palpation.20 It consisted in a

100-mm line with “no pain” at the left margin and “ex-

tremely painful” at the right margin. Participants were

seated and knee angle was 90°, while limb was totally

relaxed. Palpation was standardized by operator at 50%

of femur length. Participants were instructed to indicate

their pain sensation marking this line. Subsequently,

operator measured the distance between the left mar-

gin and the participants’ answer and such distance was

inserted in data analysis. Only the dominant limb was

tested.

Intervention

Intervention consisted in 10 sets x 10 repetitions

of squat using ywheel ergometer. Participants were

instructed to perform the concentric phase as fast as

possible and the eccentric phase until the knee angle

was approximately 90°. Two mirrors were placed in

front of participants and on their side, working as vi-

sual feedback for participant’s self-monitoring squat-

ting technique. In addition, an operator monitored each

repetition. Peak and average power for each repetition

were recorded using an encoder (SmartCoach™, Smart-

Coach Europe AB, Stockholm, Sweden) and the related

software (SmartCoach™ v.3.1.8.0). A real-time monitor

recorded the power output for each repetition and it was

showed as visual feedback for exerting each repetition

maximally. In addition, all participants were strongly

and standardly encouraged to maximally perform each

repetition. The recovery among sets was 60 seconds.

MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS CORATELLA

Vol. 56 - No. 12 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 1543

0.3-8.4, P=0.030) (Figure 4) Compared to the rst bout,

after the second bout, muscle soreness was signicantly

lower after 24 (ES=1.0, 95% CI: 0.5-1.5, P=0.002), 48

(ES=1.0, 95% CI: 0.5-1.4, P=0.001), 72 (ES=1.1, 95%

CI: 0.6-1.6, P=0.000) and 96 hours (ES=1.4, 95% CI:

0.9-1.9, P=0.000) (Figure 4).

Discussion

To the best of our knowledge, we evaluated for the

rst time muscle damage and repeated bout effect af-

ter enhanced eccentric squat exercise using a ywheel

device. We showed that muscle damage markers sig-

(P=0.005) was found for the isometric peak torque. As

a within-bout comparison, after the rst bout, compared

to baseline, isometric peak torque was signicantly

lower immediately after exercise (ES=2.8, 95% CI:

0.8-4.8, P=0.000), after 24 (ES=2.0, 95% CI: 0.5-3.5,

P=0.000), 48 (ES=1.2, 95% CI: 0.2-2.2, P=0.001) and

72 hours (ES=0.7, 95% CI: 0.0-1.4, P=0.014) (Figure

3). After the second bout, compared to baseline, iso-

metric peak torque was signicantly lower immediately

after exercise (ES=0.6, 95% CI: 0.3-0.8, P=0.000) and

after 24 hours (ES=0.4, 95% CI: 0.0-0.7, P=0.049) (Fig-

ure 3). As a between-bouts comparison, compared to the

rst bout, after the second bout, isometric peak torque

was signicantly greater after 24 (ES=0.4, 95% CI: 0.0-

0.6, P=0.029), 48 (ES=0.5, 95% CI: 0.2-0.8, P=0.001),

72 (ES=0.9, 95% CI: 0.5-1.4, P=0.000) and 96 hours

(ES=0.6, 95% CI: 0.3-0.9, P=0.002) (Figure 3).

Muscle soreness

The time course of muscle soreness values is

shown in Figure 4. Signicant time x bout interaction

(P=0.014) was found for the muscle soreness. After the

rst bout, compared to the baseline, muscle soreness

was signicantly greater after 24 (ES=5.8, 95% CI: 2.9-

8.7, P=0.000), 48 (ES=6.6, 95% CI: 3.4-9.7, P=0.000),

72 (ES=4.6, 95% CI: 2.0-7.1, P=0.001) and 96 hours

(ES=3.5, 95% CI: 1.0-6.0, P=0.004) (Figure 4). After

the second bout, compared to baseline, muscle sore-

ness was signicantly greater after 24 (ES=3.1, 95%

CI: 0.2-6.1, P=0.034) and 48 hours (ES=4.4, 95% CI:

Figure 3.—Isometric peak torque time course is showed after rst and

second bouts. Differences within and between-subjects were analyzed

by two-way repeated measures ANOVA.

*P<0.05 compared to baseline; #P<0.05 compared to the rst bout.

Figure 2.—CK blood activity time course is showed after rst and sec-

ond bouts. Differences within and between-subjects were analyzed by

two-way repeated measures ANOVA.

*P<0.05 compared to baseline; #P<0.05 compared to the second bout.

II bout

1500

101000

500

IU/L

Base 0 24 hr 48 hr 72 hr 96 hr

Time after exercise

II bout

400

10350

300

250

200

N/m

Base 0 24 hr 48 hr 72 hr 96 hr

Time after exercise

II bout

108

A.U.

Base 0 24 hr 48 hr 72 hr 96 hr

Time after exercise

Figure 4.—Muscle soreness time course is showed after rst and second

bouts. Differences within and between-subjects were analyzed by two-

way repeated measures ANOVA.

*P<0.05 compared to baseline; #P<0.05 compared to the second bout.

CORATELLA MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS

1544 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS December 2016

pants performed the eccentric-only exercise using sin-

gle-joint isokinetic or isometric-load devices. Involving

the squat exercise numerous lower limbs muscles, a sort

of load turnover among quadriceps and other synergist

muscles (e.g., hip extensors) could have limited the

quadriceps effort and consequently its strength loss.19

The muscle soreness remained signicantly above the

baseline up to 96 hours, as already reported in the litera-

ture.24 It is thought that muscle soreness could derive

from mechanical, rather than chemical, factors.20 In-

deed, the pain could be part of the mechanisms that pro-

tect muscle from a more dangerous damage subsequent

to further maximal muscle contractions.34 Conrming

such hypothesis, it has been shown that nociceptors af-

fected the motor cortex excitability by decreasing the

motor evoked potential induced by transcranial mag-

netic stimulation. 35

All the muscle damage markers, compared to the rst

bout, were signicantly lower after the second bout per-

formed 4 weeks later. Previous studies showed that the

protective effect of eccentric-only exercise was effec-

tive after 4 weeks,14, 36 and it is known that it can last

up to 6 months.9 The amounts of the initial muscle dam-

age seemed to inuence the magnitude of the repeated

bout effect.37 Interestingly, even a light eccentric-only

exercise, not followed by muscle damage symptoms,

protected muscle from a more intense eccentric-only

bout.13 In the present investigation, after the rst bout,

the muscle damage symptoms resulted smaller com-

pared to the literature.14 However, similarly to what

previously reported,13 the rst enhanced eccentric ex-

ercise conferred protection to the muscles involved in a

further subsequent enhanced eccentric bout. The repeat-

ed bout effect is typical of eccentric exercise. Indeed,

when a concentric-only exercise was carried out before

an eccentric-only exercise session, greater muscle dam-

age symptoms were measured compared to eccentric-

only exercise performed for the rst time.38 Therefore,

enhancing the eccentric exercise generated a protective

effect, which lasted for at least 4 weeks.

The mechanisms involved in the repeated bout ef-

fect are not fully understood. Three main hypothesis

were reviewed for explaining the repeated bout effect.10

Some authors suggested that an addition of in series-

sarcomere after the rst eccentric-only exercise can oc-

cur, which causes a rightward shift of the force-length

relationship.33 Therefore, the greater force produced in

nicantly increased up to 96 hours after the rst bout.

However, after the second bout, signicant decreases in

muscle damage markers occurred.

Eccentric exercise induced muscle damage has been

largely investigated in previous studies.21-23 Data exist-

ing in literature showed that muscle damage markers

resulted above the baseline up 96 hours or more.24 It

is generally accepted that muscle damage is induced

only by lengthening contraction.1 Indeed, when sarco-

meres are on the descending limb of the force-length

curve, they are instable and more prone to damage.25

Conrming such hypothesis, no muscle damage was

found after “concentric-only exercise”,26 “concentric

cycling” 27 or “step-up-only exercise”.28 Interestingly,

no muscle damage symptoms occurred after traditional

“concentric-eccentric exercise”.29 Even if the exercise

in the present investigation was not an eccentric-only

exercise, enhancing the eccentric phase led to increases

in muscle damage markers. Similarly to our outcomes,

increases in CK and lactate dehydrogenase blood activ-

ity up to 72 hours were found after one bout of supine

squat exercise using ywheel device.18

After the rst exercise bout, the CK blood activity

was signicantly higher than baseline up to 72 hours.30

The increases in CK blood activity reect ber necro-

sis. After ber disruption, the CK is rst released in the

lymphatic system and then moved in the blood ow.1

Although CK showed great inter-subjects variability,31

our results were quite homogeneous. It could in part de-

pends on the physically active population involved in

the present investigation, which showed low CK blood

activity values, as reported in previous studies.14, 32 In-

deed, when untrained participants underwent to eccen-

tric exercise, CK blood activity values resulted two-fold

greater.4

The isometric peak torque resulted signicantly low-

er than baseline up to 72 hours. The mechanisms that

affect the capacity of muscle to generate force are not

fully understood. However, it has been proposed that in-

homogeneous sarcomeres disruption could have led to a

inability to develop maximal force using contractile ele-

ments.33 Strength loss is one of the most valid and reli-

able muscle damage markers.1 The amounts of strength

decit in this study were around 15% compared to base-

line. Such strength decits are lower than those reported

in literature, in which participants experienced almost

50% of strength loss.14 However, in such study, partici-

MUSCLE DAMAGE INDUCED BY ENHANCED ECCENTRIC SQUATS CORATELLA

Vol. 56 - No. 12 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 1545

muscle damage and potential mechanisms for the repeated bout ef-

fect. Sports Med 1999;27:157-70.

9. Nosaka K, Sakamoto KEI, Newton M, Sacco P. How long does the

protective effect on eccentric exercise induced muscle damage last?

Med Sci Sport Exerc 2001;33:1490-95.

10. McHugh MP. Recent advances in the understanding of the repeated

bout effect: the protective effect against muscle damage from a sin-

gle bout of eccentric exercise. Scand J Med Sci Sports 2003;13:88-

97.

11. McHugh MP, Tetro DT. Changes in the relationship between joint

angle and torque production associated with the repeated bout effect.

J Sports Sci 2003;21:927-32.

12. Chen TC, Nosaka K. Effects of number of eccentric muscle actions

on rst and second bouts of eccentric exercise of the elbow exors. J

Sci Med Sport 2006;9:57-66.

13. Lavender AP, Nosaka K. A light load eccentric exercise confers pro-

tection against a subsequent bout of more demanding eccentric exer-

cise. J Sci Med Sport 2008;11:291-8.

14. Coratella G, Bertinato L. Isoload vs isokinetic eccentric exercise: a

direct comparison of exercise-induced muscle damage and repeated

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15. Berg HE, Tesch P. A gravity-independent ergometer to be used for re-

sistance training in space. Aviat Space Environ Med 1994;65:752-6.

16. Norrbrand L, Tous-Fajardo J, Vargas R, Tesch P. Quadriceps Muscle

Use in the Flywheel and Barbell Squat. Aviat Space Environ Med

2011;82:13-9.

17. Norrbrand L, Fluckey JD, Pozzo M, Tesch, P. Resistance training us-

ing eccentric overload induces early adaptations in skeletal muscle

size. Eur J Appl Physiol 2008;102:271-81.

18. Fernandez-Gonzalo R, Lundberg TR, Alvarez-Alvarez L, de Paz

J. Muscle damage responses and adaptations to eccentric-over-

load resistance exercise in men and women. Eur J Appl Physiol

2014;114:1075-84.

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during squat exercise depends on hip extensor muscle strategy. Sports

Biomech 2015;14:122-38.

20. Nosaka K, Newton M, Sacco P. Delayed-onset muscle soreness does

not reect the magnitude of eccentric exercise-induced muscle dam-

age. Scand J Med Sci Sports 2002;12:337-46.

21. Proske U, Allen TJ. Damage to skeletal muscle from eccentric exer-

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23. Paschalis V, Koutedakis Y, Baltzoupoulos V, Mougios V, Jamurtas

AZ, Giakas G. Short vs. long length of rectus femoris during eccen-

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26. Lavender AP, Nosaka K. Changes in uctuation of isometric force

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J Appl Physiol 2006;96:235-40.

27. Peñailillo L, Blazevich A, Numazawa H, Nosaka, K. Metabolic and

muscle damage proles of concentric versus repeated eccentric cy-

cling. Med Sci Sports Exerc 2013;45:1773-81.

28. Newham DJ, McPhail G, Mills KR, Edwards RH. Ultrastructural

changes after concentric and eccentric contractions of human muscle.

J Neurol Sci 1983;61:109-22.

29. Parr JJ, Yarrow JF, Garbo CM, Borsa PA. Symptomatic and function-

al responses to concentric-eccentric isokinetic versus eccentric-only

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31. Nosaka K, Clarkson PM. Variability in serum creatine kinase re-

the descending limb can reduce the risk of sarcomeres

overstretching.39 Other authors suggested that the

torque exerted during the eccentric-only exercise is ini-

tially distributed among a low number of motor units.5

Based on a study that showed a selective recruitment

of fast-twitch motor units during the eccentric contrac-

tion,40 it was hypothesized that a greater recruitment

of slow-twitch motor units could be recruited starting

since the second eccentric exercise session.5 There-

fore, a torque exertion re-distribution could involve a

higher number of motor units, decreasing the pro-ber

mechanical stress and consequently the risk of sarco-

meres over-stretching. Finally, other authors hypoth-

esized a re-arrangement of the non-contractile elements

properties.41 Particularly, the greater muscle stiffness

found after eccentric exercise, can reduce the risk of

muscle damage.41 Although each hypothesis showed its

strength and weakness points,10 within this study design

we are not able to indicate one of them as more likely.

Conclusions

In conclusion, the enhanced eccentric exercise in-

duced symptoms of muscle damage up to 96 hours af-

ter the rst bout. When, 4 weeks later, the same bout

was performed, muscle damage symptoms were signi-

cantly smaller compared to the rst bout. The enhanced

eccentric exercise squat performed using a ywheel

ergometer provided muscle protection from the second

bout performed 4 weeks later.

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Conicts of interest.—The authors certify that there is no conict of interest with any nancial organization regarding the material discussed in the manuscript.

Article rst published online: November 27, 2015. - Manuscript accepted: November 25, 2015. - Manuscript revised: November 11, 2015. - Manuscript

received: July 10, 2015.

Impact of Eccentric versus Concentric Cycling Exercise on Neuromuscular Fatigue and Muscle Damage in Breast Cancer Patients

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Jun 2024
MED SCI SPORT EXER

Introduction This study investigated the magnitude and etiology of neuromuscular fatigue and muscle damage induced by eccentric cycling compared to conventional concentric cycling in patients with breast cancer. Methods After a gradual familiarization protocol for eccentric cycling, nine patients with early-stage breast cancer performed three cycling sessions in eccentric or concentric mode. The eccentric cycling session (ECC) was compared to concentric cycling sessions matched for power output (CON power, 80% of concentric peak power output, 95 ± 23 W) or oxygen uptake ( 10 ± 2 mL.min.kg ⁻¹ ). Pre- to postexercise changes (30s through 10 min recovery) in knee extensor maximal voluntary contraction force (MVC), voluntary activation, and quadriceps potentiated twitch force (Q tw ) were quantified to determine global, central, and peripheral fatigue, respectively. Creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured in the plasma before and 24 h postexercise as markers of muscle damage. Results Compared to CON power (-11 ± 9%) and (-5 ± 5%), the ECC session resulted in a greater decrease in MVC (-25 ± 12%) postexercise ( P < 0.001). Voluntary activation decreased only in ECC (-9 ± 6% postexercise, P < 0.001). The decrease in Q tw was similar postexercise between ECC and CON power (-39 ± 21% and -40 ± 16%, P > 0.99) but lower in ( P < 0.001). The CON power session resulted in twofold greater compared to the ECC and sessions ( P < 0.001). No change in CK or LDH activity was reported from preexercise to 24 h postexercise. Conclusions The ECC session induced greater neuromuscular fatigue compared to the concentric cycling sessions without generating severe muscle damage. ECC is a promising exercise modality for counteracting neuromuscular maladaptation in patients with breast cancer.

Effects of single and repeated bouts of flywheel exercise on jump performance and muscle damage in athletes and non athletes

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Background Although recent studies have investigated the effects of flywheel (FW) training on muscle function, the effects of transient FW exercise on jump performance in athletes are unknown. This study examined the effects of single and repeated bouts of FW squat exercises on jump performance and muscle damage in male collegiate basketball players. Methods The participants were 10 healthy college-age men (nonathletes) and 11 male basketball players (athletes). The intervention involved 100 squat exercises (10 repetitions × 10 sets) using an FW device. To examine the repeated-bout effects, the protocol was conducted again after a 2-week interval. Squat jumps, countermovement jumps, drop jumps, and rebound jumps were evaluated as jump performance, while isometric maximal voluntary contraction (MVC) torque in knee extension, muscle soreness, range of motion, thigh circumference, muscle thickness, and echo intensity were evaluated as markers of muscle damage. Measurements were taken at baseline, immediately after exercise, 24 h later, and 72 h later. Results The jump performance of nonathletes decreased after exercise (p < 0.05), while that of the athletes did not. The results were similar for muscle soreness. MVC torque decreased significantly after the first exercise in both groups (p < 0.05) and was significantly lower in the nonathletes versus athletes. Significant repeated-bout effects were found for muscle soreness in nonathletes but not athletes. Conclusions These results suggest that a single bout of FW exercise reduces jump performance in male nonathletes but not basketball players.

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Eight‐Week Flywheel Training Enhances Jump Performance and Stretch‐Shortening Cycle Function in Collegiate Basketball Players

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EUR J SPORT SCI

The effects of flywheel (FW) training on jump performance, muscle function, and muscle mass in athletes have not been fully clarified. The purpose of the present study was to evaluate the effects of an 8‐week FW training program on jump performance, stretch‐shortening cycle (SSC) function, muscle strength, peak power and muscle thickness in collegiate basketball players. Twenty male college basketball players (mean age: 19.8 ± 1.3 years, height: 179.1 ± 6.7 cm, body mass: 72.9 ± 6.3 kg) were randomly assigned to either the FW training (n = 11) or control group (n = 9). The FW training group performed squat exercises, 5 sets of 8 repetitions, twice a week using the FW device. Baseline and post‐training assessments of jump heights of squat jumps (SJs), countermovement jumps (CMJs), and drop jumps (DJs) were performed in both groups. Additionally, the reactive strength index (RSI), representing SSC function; isometric maximum voluntary contraction (MVC) torque during knee joint extension; peak power during squats; and quadriceps muscle thickness were evaluated. As the results, we observed that the FW training group demonstrated significant increases in post‐training SJ height (15.1%, p = 0.03), DJ height (23.2%, p = 0.01), RSI (36.8%, p = 0.04), MVC, peak power and muscle thickness compared with pre‐training levels. Furthermore, between‐group comparisons indicated significantly higher post‐training SJ height, DJ height, RSI, MVC, peak power, and muscle thickness in the FW training group (p < 0.05). Therefore, the FW training program effectively enhanced jump performance and SSC function in male basketball players and proved beneficial for muscle strength and hypertrophy.

The impact of flywheel resistance squat training on lower limb strength in female college basketball players

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Nov 2024

Objective This study compared the effects of Flywheel Resistance Squat Training (FRST) vs. Traditional Resistance Squat Training (TRST) on lower body strength in female collegiate basketball players. Methods Nineteen participants were randomly assigned to either the FRST group (n = 9) or the TRST group (n = 10) through a random number draw. Both groups underwent a 6-week intervention with training sessions conducted twice a week. The FRST group utilized an inertia of 0.075 kg ·m², while another group trained at 80% of their one-repetition maximum (1RM). Each training session consisted of 4 sets of 8 repetitions with a 3-minute rest between sets. Both groups performed standardized warm-ups and stretches before and after each training session. The effectiveness of the training methods was assessed through the Countermovement Jump (CMJ), Reactive Strength Index (RSI), Eccentric Utilization Ratio, Running Vertical Jump, and 1RM squat. Results The FRST and TRST groups showed differences within groups in both CMJ and 1RM squat (p < 0.01), with the FRST group demonstrating moderate effect sizes in CMJ (Hedges’ g = 0.59) and 1RM (Hedges’ g = 1.01). However, there were no differences between groups (p > 0.05). The Eccentric Utilization Ratio showed a small effect size (p = 0.78; η p 2 = 0.01 ). Additionally, Reactive Strength Index and Running Vertical Jump exhibited low test-retest reliability. Conclusion The two groups did not exhibit a statistically significant difference. Nonetheless, both FRST and TRST demonstrated positive effects on 1RM squat and CMJ performance compared to baseline values for each method. Therefore, flywheel resistance training can be considered an effective alternative to traditional resistance training for enhancing strength levels in female basketball players.

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EUR J APPL PHYSIOL

Purpose To examined the time-course of the early and late phase of the rate of voluntary force development (RVFD) and muscle damage markers after downhill running. Methods Ten recreational runners performed a 30-min downhill run at 10 km h⁻¹ and −20% (−11.3°) on a motorized treadmill. At baseline and each day up to 4 days RVFD, knee extensors maximum voluntary isometric force (MVIC), serum creatine kinase (CK) concentration, quadriceps swelling, and soreness were assessed. The early (0–50 ms) and late (100–200 ms) phase of the RVFD, as well as the force developed at 50 and 200 ms, were also determined. Results MVIC showed moderate decrements (p < 0.05) and recovered after 4 days (p > 0.05). Force at 50 ms and the early phase were not impaired (p > 0.05). Conversely, force at 200 ms and the late phase showed moderate decrements (p < 0.05) and recovered after 3 and 4 days, respectively (p > 0.05). CK concentration, quadriceps swelling, and soreness increased (p < 0.05) were overall fully resolved after 4 days (p > 0.05). Conclusion Downhill running affected the knee extensors RVFD late but not early phase. The RVFD late phase may be used as an additional marker of muscle damage in trail running.

EFFECTS OF TWO DIFFERENT FLYWHEEL RESISTANCE TRAINING PROTOCOLS ON EXPLOSIVE KNEE EXTENSION STRENGTH: A PILOT RANDOMIZED STUDY

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The aim of our study was to evaluate differences in explosive isometric knee extension strength adaptations after a flywheel squat resistance training programs performed under low- and high-load conditions. Twenty physically active adults were randomly assigned to an individually allocated high- or low-load eight-week training intervention. Isometric knee extension rate of torque development (RTD) and rate of electromyography signal rise (RER) variables were assessed pre and post eight-week intervention. Statistically significant improvements in the RTD slope variables (100 and 200 ms time intervals after the onset of torque rise; p < 0,05) were observed, regardless of the training load used. Normalized averaged vastus lateralis and rectus femoris electromyography (EMG) amplitude decreased in the intervals 80 ms before, and 75, 100 and 200 ms after the onset of activation (all p < 0,05), regardless of the training group. Our results suggest that high- and low-load resistance flywheel training interventions induce similar increases in explosive knee extension strength, accompanied with a decrease in time-analog normalized EMG signal amplitude.

Biceps Brachii and Brachioradialis Excitation in Biceps Curl Exercise: Different Handgrips, Different Synergy

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Mar 2023

The current study analyzed the excitation of biceps brachii, brachioradialis, and anterior deltoid during bilateral biceps curl performed with different handgrips. Ten competitive bodybuilders performed bilateral biceps curl in non-exhaustive 6-rep sets using 8-RM with the forearm in supinated, pronated, and neutral positions. The ascending and descending phase of each variation was separately analyzed using the normalized root mean square collected using surface electromyography. During the ascending phase, (i) biceps brachii excitation was greater with the supinated compared to the pronated [+19(7)%, ES: 2.60] and neutral handgrip [+12(9)%, ES: 1.24], (ii) the brachioradialis showed greater excitation with the supinated compared to the pronated [+5(4)%, ES: 1.01] and neutral handgrip [+6(5)%, ES: 1.10], (iii) the anterior deltoid excitation was greater with the pronated and neutral handgrip compared to the supinated condition [+6(3)% and +9(2)%, ES: 2.07 and 3.18, respectively]. During the descending phase, the anterior deltoid showed greater excitation in the pronated compared to the supinated handgrip [+5(4)%, ES: 1.02]. Changing the handgrips when performing biceps curl induces specific variations in biceps brachii and brachioradialis excitation and requires different anterior deltoid interventions for stabilizing the humeral head. Practitioners should consider including different handgrips in the biceps curl routine to vary the neural and mechanical stimuli.

Influence of Cluster Sets on Mechanical and Perceptual Variables in Adolescent Athletes

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Full-text available

Feb 2023
Int J Environ Res Publ Health

Cluster sets (CS) are effective in maintaining performance and reducing perceived effort compared to traditional sets (TRD). However, little is known about these effects on adolescent athletes. The purpose of this study was to compare the effect of CS on the performance of mechanical and perceptual variables in young athletes. Eleven subjects [4 boys (age = 15.5 ± 0.8 years; body mass = 54.3 ± 7.0 kg; body height = 1.67 ± 0.04 m; Back Squat 1RM/body mass: 1.62 ± 0.19 kg; years from peak height velocity [PHV]: 0.94 ± 0.50) and 7 girls (age = 17.2 ± 1.4 years; body mass = 54.7 ± 6.3 kg; body height = 1.63 ± 0.08 m; Back Squat 1RM/body mass: 1.22 ± 0.16 kg; years from PHV: 3.33 ± 1.00)] participated in a randomized crossover design with one traditional (TRD: 3 × 8, no intra-set and 225 s interest rest) and two clusters (CS1: 3 × 2 × 4, one 30 s intra-set and 180 s inter-set rest; and CS2: 3 × 4 × 2, three 30 s intra-set and 90 s inter-set rest) protocols. The subjects were assessed for a Back Squat 1RM for the first meet, then performed the three protocols on three different days, with at least 48 h between them. During experimental sessions, a back squat exercise was performed, and mean propulsive velocity (MPV), power (MPP), and force (MPF) were collected to analyze performance between protocols, together with measures of countermovement jump (CMJ) and perceptual responses through Rating of Perceived Exertion for each set (RPE-Set) and the overall session (S-RPE), and Muscle Soreness (DOMS). The results showed that velocity and power decline (MVD and MPD) were favorable for CS2 (MVD: −5.61 ± 14.84%; MPD: −5.63 ± 14.91%) against TRD (MVD: −21.10 ± 11.88%; MPD: −20.98 ± 11.85%) (p < 0.01) and CS1 (MVD: −21.44 ± 12.13%; MPD: −21.50 ± 12.20%) (p < 0.05). For RPE-Set, the scores were smaller for CS2 (RPE8: 3.23 ± 0.61; RPE16: 4.32 ± 1.42; RPE24: 4.46 ± 1.51) compared to TRD (RPE8: 4.73 ± 1.33; RPE16: 5.46 ± 1.62; RPE24: 6.23 ± 1.97) (p = 0.008), as well as for Session RPE (CS2: 4.32 ± 1.59; TRD: 5.68 ± 1.75) (p = 0.015). There were no changes for jump height (CMJ: p = 0.985), and the difference between time points in CMJ (ΔCMJ: p = 0.213) and muscle soreness (DOMS: p = 0.437) were identified. Our findings suggest that using CS with a greater number of intra-set rests is more efficient even with the total rest interval equalized, presenting lower decreases in mechanical performance and lower perceptual effort responses.

The reliability of functional and systemic markers of muscle damage in response to a flywheel squat protocol

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Full-text available

Nov 2024
EUR J APPL PHYSIOL

Purpose To characterize the magnitude, timescale, and reliability of changes in functional and systemic outcome markers following moderate (MIR) and high (HIR) isoinertial resistance flywheel squat protocols (FSP). Methods Twenty-four resistance-trained males completed two exercise trials (ET1 & ET2) separated by 32 days. Functional and systemic markers were assessed at pre-exercise (PRE), immediately post-exercise (IP), and 24 (24H), 48 (48H), and 72 (72H) hours post-exercise. Three-way group x trial x time repeated measures ANOVAs were conducted to compare all dependent variables between groups (MIR & HIR) and experimental trials across time. Test–retest reliability between trials was assessed using intraclass correlation coefficients (ICC). Results At IP, both groups exhibited significantly decreased active range of motion, perceived recovery status, squat maximal voluntary isometric contraction force, and vertical jump performance, along with significantly increased muscle thickness and echo intensity (ultrasound), muscle soreness, and creatine kinase when compared to PRE. Most outcomes remained perturbed at 24H and 48H, especially in the HIR group. By 72H, only a subset of variables remained significantly changed from PRE. No significant attenuation of outcomes between trials were observed and test–retest reliability between trials was excellent for the FSP and moderate to excellent for most outcomes in both groups. Conclusion Our findings indicate that the FSP is a robust and repeatable exercise stimulus capable of eliciting significant exercise-induced muscle damage and reliable subsequent perturbations to functional and systemic markers of muscle damage. Our findings also support the use of crossover designs in future EIMD research designs with resistance-trained men.

Quadriceps effort during squat exercise depends on hip extensor muscle strategy

Article

Full-text available

Apr 2015

Hip extensor strategy, specifically relative contribution of gluteus maximus versus hamstrings, will influence quadriceps effort required during squat exercise, as hamstrings and quadriceps co-contract at the knee. This research examined the effects of hip extensor strategy on quadriceps relative muscular effort (RME) during barbell squat. Inverse dynamics-based torque-driven musculoskeletal models were developed to account for hamstrings co-contraction. Net joint moments were calculated using 3D motion analysis and force platform data. Hamstrings co-contraction was modelled under two assumptions: (1) equivalent gluteus maximus and hamstrings activation (Model 1) and (2) preferential gluteus maximus activation (Model 2). Quadriceps RME, the ratio of quadriceps moment to maximum knee extensor strength, was determined using inverse dynamics only, Model 1 and Model 2. Quadriceps RME was greater in both Models 1 and 2 than inverse dynamics only at barbell loads of 50-90% one repetition maximum. The highest quadriceps RMEs were 120 ± 36% and 87 ± 28% in Models 1 and 2, respectively, which suggests that barbell squats are only feasible using the Model 2 strategy prioritising gluteus maximus versus hamstrings activation. These results indicate that developing strength in both gluteus maximus and quadriceps is essential for lifting heavy loads in squat exercise.

Isoload vs isokinetic eccentric exercise: a direct comparison of exercise-induced muscle damage and repeated bout effect

Article

Full-text available

Oct 2014

Purpose This study compared the exercise induced muscle damage and repeated bout effect after isoload vs isokinetic eccentric supra-maximal single session. Methods Thirty sport science male students were ran-domly divided in isokinetic (IK) and isoload (IL) eccentric training. Creatin kinase (CK) serum activity, muscle sore-ness and strength decrement measured both in dynamic and isometric modalities were recorded at baseline, immedi-ately after and up to 4 days following 48 supramaximal IK or IL eccentric contractions. Same protocol was repeated after 4 weeks. A three-way repeated measures ANOVA was used to detect differences in dependent variables comparing group 9 bout 9 time. Results No three-way interaction occurred in dependent variables. Bout 9 time resulted in a significant interaction in all dependent variables. Muscle damage markers resul-ted significantly altered compared to baseline up to 4 days. However, IL showed significantly greater CK, muscle soreness and strength deficit compared to IK. All parame-ters were significantly reduced after second compared to first bout. Difference between IL and IK after second bout was not overall significant. Conclusion IK vs IL supra-maximal eccentric contraction is showed to have different muscle damage symptoms. Protection conferred by first bout reduced muscle damage after 4 weeks and decreased difference between IL and IK.

Muscle damage responses and adaptations to eccentric-overload resistance exercise in men and women

Article

Full-text available

Feb 2014
EUR J APPL PHYSIOL

This study assessed markers of muscle damage and training adaptations to eccentric-overload flywheel resistance exercise (RE) in men and women. Dynamic strength (1 RM), jump performance, maximal power at different percentages of 1 RM, and muscle mass in three different portions of the thigh were assessed in 16 men and 16 women before and after 6 weeks (15 sessions) of flywheel supine squat RE training. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) concentrations were measured before, 24, 48 and 72 h after the first and the last training session. After training, increases in 1 RM were somewhat greater (interaction P < 0.001) in men (25 %) than in women (20 %). Squat and drop jump height and power performance at 50, 60, 70 and 80 % of 1 RM increased after training in both sexes (P < 0.05). Power improvement at 80 % of 1 RM was greater (interaction P < 0.02) in men than women. Muscle mass increased ~5 % in both groups (P < 0.05). CK increased in men after the first training session (P < 0.001), whereas the response in women was unaltered. In both sexes, LDH concentration was greater after the first training session compared with basal values (P < 0.05). After the last session, CK and LDH remained at baseline in both groups. These results suggest that although improvements in maximal strength and power at high loads may be slightly greater for men, eccentric-overload RE training induces comparable and favorable gains in strength, power, and muscle mass in both men and women. Equally important, it appears muscle damage does not interfere with the adaptations triggered by this training paradigm.

Metabolic and Muscle Damage Profiles of Concentric versus Repeated Eccentric Cycling

Article

Full-text available

Mar 2013
MED SCI SPORT EXER

Purpose: Eccentric cycling is an exercise modality that could elicit multiple health benefits with low metabolic cost, but unaccustomed performance results in significant muscle damage. It is not known whether muscle damage is attenuated when eccentric cycling is repeated; thus, this study compared metabolic and muscle damage responses to concentric (CONC) and two consecutive eccentric (ECC1 and ECC2) cycling bouts. Methods: Ten men (28 ± 8 yr) performed each cycling bout for 30 min at 60% of the maximal concentric power output at 60 rpm, with 2 wk between bouts. HR, oxygen consumption (V˙O2), blood lactate (BLa), RPE, and muscle activity (EMG) data were collected during cycling. Maximal voluntary isometric knee extensor (MVC) strength, squat (SJ), countermovement jump (CMJ) height, muscle soreness indicators, and plasma creatine kinase (CK) activity were measured before, immediately after, and 1-4 d after exercise. Results: Average HR, V˙O2, BLa, and RPE were lower (P < 0.05) during ECC1 than CONC, and EMG amplitude was also lower during ECC1 than CONC. Decreases in MVC, CMJ, and SJ and the increase in muscle soreness were greater (P x0003C; 0.05) after ECC1 than CONC. Increases in creatine kinase were minimal after all bouts. When comparing ECC1 and ECC2, HR and BLa were lower (P < 0.05) during ECC2 than ECC1, and decreases in MVC, CMJ, and SJ and the increase in muscle soreness were greater (P < 0.05) after ECC1 than ECC2. After ECC2, MVC, CMJ, and SJ did not change and no muscle soreness was developed. Conclusions: Eccentric cycling was less metabolically demanding than concentric cycling, and HR and BLa were further reduced during ECC2. Muscle damage is minimal after ECC2 and should not influence the choice to undertake eccentric cycling training.

Quadriceps Muscle Use in the Flywheel and Barbell Squat

Article

Full-text available

Jan 2011
AVIAT SPACE ENVIR MD

Resistance exercise has been proposed as an aid to counteract quadriceps muscle atrophy in astronauts during extended missions in orbit. While space authorities have advocated the squat exercise should be prescribed, no exercise system suitable for in-flight use has been validated with regard to quadriceps muscle use. We compared muscle involvement in the terrestrial "gold standard" squat using free weights and a nongravity dependent flywheel resistance exercise device designed for use in space. The subjects were 10 strength-trained men who performed 5 sets of 10 repetitions using the barbell squat (BS; 10 repetition maximum) or flywheel squat (FS; each repetition maximal), respectively. Functional magnetic resonance imaging (MRI) and surface electromyography (EMG) techniques assessed quadriceps muscle use. Exercise-induced contrast shift of MR images was measured by means of transverse relaxation time (T2). EMG root mean square (RMS) was measured during concentric (CON) and eccentric (ECC) actions and normalized to EMG RMS determined during maximal voluntary contraction. The quadriceps muscle group showed greater exercise-induced T2 increase following FS compared with BS. Among individual muscles, the rectus femoris displayed greater T2 increase with FS (+24 +/- 14%) than BS (+8 +/- 4%). Normalized quadriceps EMG showed no difference across exercise modes. Collectively, the results of this study suggest that quadriceps muscle use in the squat is comparable, if not greater, with flywheel compared with free weight resistance exercise. Data appear to provide support for use of flywheel squat resistance exercise as a countermeasures adjunct during spaceflight.

Intensity of eccentric exercise, shift of optimum angle, and the magnitude of repeated-bout effect

Article

Full-text available

Symptomatic and Functional Responses to Concentric-Eccentric Isokinetic Versus Eccentric-Only Isotonic Exercise

Article

Full-text available

Sep 2009
J ATHL TRAINING

Rehabilitation protocols involving eccentric resistance exercise performed with loading more than 100% concentric 1-repetition maximum are effective in increasing muscle function in both healthy and injured populations. The mode of eccentric exercise (isokinetic versus isotonic) may be an important factor in limiting symptoms of delayed-onset muscle soreness and in improving muscle function after training. To compare functional and symptomatic responses after an eccentric-only (ECC) isotonic exercise protocol and after a combined concentric-eccentric (CON-ECC) isokinetic exercise protocol matched for total exercise volume. Observational study. Controlled research laboratory. Twenty-four healthy, untrained, college-aged men (n = 12) and women (n = 12). Participants were randomly assigned to the ECC isotonic or CON-ECC isokinetic exercise group and performed a single bout of resistance exercise involving the elbow flexors. Measurements of elbow flexion and extension, isometric strength, and muscle point tenderness were obtained before exercise (baseline) and during follow-up sessions (days 2, 4, 7, and 14). Separate 1-way analyses of variance and repeated-measures analyses of variance were used to determine outcome differences. Tukey post hoc testing was performed when indicated. At baseline, no differences were present between groups for any measure. The ECC isotonic exercise protocol resulted in a 30% to 36% deficit in muscle strength, a 5% to 7% reduction in elbow flexion, and a 6% to 8% reduction in elbow extension at follow-up days 2 and 4 (P < .01). The CON-ECC isokinetic exercise protocol did not alter muscle strength or range of motion at any time when compared with baseline. Muscle point tenderness increased from baseline on days 2 and 4 in both groups (P < .05) but was not different between groups throughout the recovery period. Our results indicated more pronounced functional deficits occurred after a single bout of ECC isotonic exercise than with a CON-ECC isokinetic exercise protocol matched for training volume.

Isokinetic Eccentric Exercise of Quadriceps Femoris Does Not Affect Running Economy

Article

Jul 2008
J STRENGTH COND RES

The purpose of this study was to investigate whether running economy is affected by isokinetic eccentric exercise designed to cause muscle damage. Twenty-four young healthy men performed 120 maximal voluntary eccentric actions at each thigh's quadriceps muscle at an angular velocity of 60 degrees .s. The participants were then randomly divided into 2 equal groups, 1 of which exercised 24 hours later, while the other group rested. Muscle damage indicators (i.e., serum creatine kinase, delayed onset muscle soreness, and eccentric, concentric, and isometric peak torque) and running economy indicators (i.e., oxygen consumption, pulmonary ventilation, respiratory exchange ratio, respiratory rate, and heart rate during treadmill running at 2.2 and 3.3 m.s) were assessed prior to and 48 hours following the eccentric exercise. All muscle damage indicators changed significantly in both groups (p < 0.05) in a way suggestive of considerable muscle damage. Running economy indicators of the exercise group demonstrated only an elevation of respiratory rate at 48 hours (p < 0.05) and a tendency to lower economy compared to the resting group. It can be concluded that isokinetic eccentric exercise applied to the quadriceps femoris muscles did not affect running economy 48 hours later and that resting during this period tended to result in more economical running compared to exercising at 24 hours.

New insights into the behavior of muscle during active lengthening

Article

Mar 1990

David L Morgan

A muscle fiber was modeled as a series-connected string of sarcomeres, using an A. V. Hill type model for each sarcomere and allowing for some random variation in the properties of the sarcomeres. Applying stretches to this model led to the prediction that lengthening of active muscle on or beyond the plateau of the length tension curve will take place very nonuniformly, essentially by rapid, uncontrolled elongation of individual sarcomeres, one at a time, in order from the weakest toward the strongest. Such a "popped" sarcomere, at least in a single fiber, will be stretched to a length where there is no overlap between thick and thin filaments, and the tension is borne by passive components. This prediction allows modeling of many results that have previously been inexplicable, notably the permanent extra tension after stretch on the descending limb of the length tension curve, and the continued rise of tension during a continued stretch.

Selective recruitment of high-threshold human motor units during voluntary isotonic lengthening of active muscles

Article

Mar 1989

1. We have investigated the possibility that voluntary muscle lengthening contractions can be performed by selective recruitment of fast-twitch motor units, accompanied by derecruitment of slow-twitch motor units. 2. The behaviour of motor units in soleus, gastrocnemius lateralis and gastrocnemius medialis muscles was studied during (a) controlled isotonic plantar flexion against a constant load (shortening contraction, S), maintained plantar flexion, or dorsal flexion resisting the load and gradually yielding to it (lengthening contraction, L), (b) isometric increasing or decreasing plantar torque accomplished by graded contraction or relaxation of the triceps surae muscles, (c) isometric or isotonic ballistic contractions, and (d) periodic, quasi-sinusoidal isotonic contractions at different velocities. The above tasks were performed under visual control of foot position, without activation of antagonist muscles. The motor units discharging during foot rotation were grouped on the basis of the phase(s) during which they were active as S, S + L and L. The units were also characterized according to both the level of isometric ramp plantar torque at which they were first recruited and the amplitude of their action potential. 3. S units were never active during dorsal flexion; some of them were active during the sustained contraction between plantar and dorsal flexion. Most S + L units were active also during the maintenance phase and were slowly derecruited during lengthening; their behaviour during foot rotations was similar to that during isometric contractions or relaxations. L units were never active during either plantar or maintained flexion, but discharged during lengthening contraction in a given range of rotation velocities; the velocity of lengthening consistently influenced the firing frequency of these units. Such dependence on velocity was not observed in S + L units. 4. A correlation was found between the amplitude of the action potential and the threshold torque of recruitment among all the units. In addition, the amplitudes of both the action potential and the threshold torque were higher in the case of L units than in the case of S and S + L units. Most L units could be voluntarily recruited only in the case of ballistic isometric or isotonic contraction. 5. Occasionally, L units were directly activated by electrical stimulation of motor fibres and their conduction velocity was in the higher range for alpha-axons. In contrast, nerve stimulation could induce a reflex activation of S and S + L units.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscle damage and repeated bout effect induced by enhanced-eccentric squat exercise

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