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Journal of Exercise Physiologyonline
February 2013
Volume 16 Number 1
Editor-in-Chief
Official Research Journal of
Tommy
the American
Boone, PhD,
Society
MBA
of
Review
Board
Exercise
Physiologists
Todd Astorino, PhD
ISSN 1097-9751
Julien Baker,
PhD
Steve Brock, PhD
Lance Dalleck, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Yit Aun Lim, PhD
Lonnie Lowery, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Robert Robergs, PhD
Chantal Vella, PhD
Dale Wagner, PhD
Frank Wyatt, PhD
Ben Zhou, PhD
Official Research Journal
of the American Society of
Exercise Physiologists
ISSN 1097-9751
JEPonline
The Effects of Concentric Fatigue on Concentric,
Eccentric, and Isometric Torque
Robert W. Lewis Jr., Terry J. Housh, Daniel A. Traylor, Haley C.
Bergstrom, Glen O. Johnson, Richard J. Schmidt, Joel T. Cramer,
Nathaniel D.M. Jenkins, Kristen C. Cochrane
University of Nebraska-Lincoln, Lincoln, NE
ABSTRACT
Lewis Jr., RW, Housh, TJ, Traylor, DT, Bergstrom, HC, Johnson,
GO, Schmidt, RJ, Cramer, JT, Jenkins, NDM, Cochrane, KC. The
Effects of Concentric Fatigue on Concentric, Eccentric, and Isometric
Torque. JEPonline 2013;16(1):10-18. Fatiguing concentric (CON)
muscle actions of the leg extensors have been shown to result in
differences in percent (%) decline in torque for CON, eccentric (ECC),
and isometric (ISO) muscle actions. However, the effects of CON
fatigue of the forearm flexors on CON, ECC, and ISO torque have not
been well established. The purpose of this investigation was to
determine the effects of 50 maximal CON isokinetic forearm flexion
muscle actions on CON, ECC, and ISO torque. Sixteen adults (8 men
(mean ± SD = 23.1 ± 2.3) and 8 women (mean ± SD age = 22.8 ±
1.4)) volunteered to perform 50 consecutive, CON forearm flexion
muscle actions at 180°·s-1. Before and after the fatiguing workbout,
peak torque was measured (randomly ordered) for CON, ECC, and
ISO muscle actions. Polynomial regression analysis indicated a cubic
(R2 = 0.98) pattern of response during the 50 CON muscle actions.
There were no differences in mean % decline (30%) in torque among
the three types of muscle actions. The findings indicate that the CON,
ECC, and ISO muscle actions share a common mechanism of fatigue
as a result of the fatiguing CON workbout.
Key Words: Isokinetics, Fatigue
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INTRODUCTION
Fatigue has been defined as “…any reduction in the force generating capacity of the total
neuromuscular system regardless of the force required in any given situation” (4, p. 691). A number
of previous investigations have examined the effects of fatigue induced by one type of muscle action
(e.g., concentric) on the maximal torque produced by different types of muscle actions (e.g., eccentric
or isometric) (3,5,7,9,13,15,16,20,21,23). In general, most studies have examined the leg extensor
muscles of which the researchers have reported that there are mode-specific differences in the effect
of the type of fatiguing muscle actions on concentric (CON), eccentric (ECC), and isometric (ISO)
torque (5,13,15,18). For example, Michaut et al. (15) reported a greater decline in ECC (16.8%) than
CON torque (10%) following 100 maximal, CON isokinetic muscle actions of the leg extensors.
In addition, previous investigations (9,16,20,21) have reported that fatiguing ECC muscle actions of
the leg extensors resulted in 25-77%, 25-53%, and 45-82% declines in CON, ECC, and ISO torque,
respectively. The mode-specific nature of the % declines in torque from the previous studies of the
leg extensors (5,13,15,18) may have been due to factors such as the velocity of the muscle actions
and the number of repetitions performed. For the forearm flexors, however, Beck et al. (3) reported
similar declines in CON, ECC, and ISO torque (mean = 26% decline) following both fatiguing CON
and ECC muscle actions. Thus, torque production following a fatiguing workbout may also depend on
the muscle group involved and the type of muscle action tested.
Mode-specific declines in torque have been attributed to the build-up of metabolic byproducts and/or
damage to the myofibrils caused by ECC muscle actions. Specifically, it has been suggested (6,8,11)
that fatigue resulting from CON muscle actions is due to the build-up of ammonia, hydrogen ions,
potassium, and inorganic phosphate. Fatigue resulting from ECC muscle actions may be due to both
the build-up of metabolic byproducts and damage to the myofibril (e.g., sarcomere derangement,
swollen mitochondria, fragmented or swollen sarcoplasmic reticular elements, dilated T-tubules, and
lesions in the plasma membrane) (22). Thus, the results of previous studies (5,7,9,13-16,20,21,23)
suggest there may be mode-specific responses to fatigue.
The purpose of this study was to determine the effects of 50 maximal CON isokinetic muscle actions
of the forearm flexors on CON, ECC, and ISO torque. Based on the results of previous studies (5,7,9,
13-16,20,21,23), we hypothesized that there would be differences in % decline in torque among the
CON, ECC, and ISO muscle actions.
METHODS
Subjects
Eight men (mean ± SD age = 22.1 ± 2.3 yrs; height = 182 ± 6.5 cm; body mass = 75.3 ± 30.5 kg) and
8 women (age = 22.8 ± 1.4 yrs; height = 171.1 ± 7.0 cm; body mass = 65.1 ± 8.7 kg) volunteered to
participate in this investigation. The subjects were moderately active, participating in physical activity
3-5 times per week. The study was approved by the University Institutional Review Board for Human
Subjects, and all subjects completed a health history questionnaire and signed a written informed
consent prior to testing.
Procedures
Prior to the isokinetic testing, the subjects performed a familiarization session. During this session,
the subjects were positioned in accordance with the Cybex 6000 owner’s manual to perform: (a) three
CON isokinetic forearm flexion muscle actions; (b) three ECC muscle actions of the forearm flexors at
a velocity of 180°·s-1; and (c) three ISO muscle actions of the forearm flexors for 3 sec each at an
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angle of 115° between the arm and forearm. The subjects were instructed to provide an effort
corresponding to approximately 50% of their maximum during the familiarization session.
Forty-eight to 72 hrs after the familiarization session, the subjects performed the testing session and
fatiguing workbout. They were instructed not to perform upper body resistance training during the 48
hrs prior to the testing session. The testing session began with a warm-up that was identical to the
familiarization session, followed by 2 min of rest. Then, they performed a pre-test, fatiguing workbout,
and post-test. The pre- and post-tests consisted of three maximal, CON and ECC isokinetic forearm
flexion muscle actions at a velocity of 180°·s-1, as well as three maximal ISO (3 sec) forearm flexion
muscle actions at an angle of 115° between the arm and forearm. Passive extension followed each
CON muscle action, and passive flexion preceded each ECC muscle action. The order of the CON,
ECC, and ISO muscle actions were randomized for the pre-test and the same order was used for the
post-test. The repetitions, which produced the highest torque for each of the three muscle actions
(CON, ECC, and ISO) from the pre- and post-tests, were used as representative scores for each
subject.
Previous test-retest reliability data from our laboratory for CON isokinetic forearm flexion torque at
180°·s-1, as well as ISO torque of the forearm flexors at a joint angle of 115° indicated that for young
adult male subjects (n = 10) measured 2 d apart, the intraclass correlation (R) was 0.99. Test-retest
reliability from our laboratory for 10 adult subjects measured 24 to 48 hrs apart for ECC isokinetic
torque of the forearm flexors at a velocity of 180°·s-1 resulted in an intraclass correlation (R) of 0.91.
Furthermore, there were no significant differences (P>0.05) between the test and retest measures for
the CON, ECC, or ISO torque values.
The pre-test was immediately (~3 to 5 sec) followed by the fatigue protocol, which consisted of 50
consecutive maximal CON isokinetic forearm flexion muscle actions at a velocity of 180°·s -1. The
post-test began ~3 to 5 sec following the fatiguing CON workbout and took 30 to 45 sec to complete.
Strong verbal encouragement to perform maximal effects was provided for each subject throughout
the entire data collection process (pre-test, fatiguing CON workbout, and post-test).
Statistical Analyses
The data were analyzed using a two (pre-test vs. post-test) x three (CON vs. ECC vs. ISO torque)
repeated measures ANOVA. Follow-up analyses included a one-way repeated measures ANOVA
and paired t test (P<0.05). The relationships for torque versus repetition number were examined
using polynomial regression analyses (linear, quadratic, and cubic; SPSS software program, V. 20.0
IBM SPSS Inc., Chicago, Illinois, USA). The statistical significance (P<0.05) for the increment in the
proportion of the variance that was accounted for by a higher degree polynomial was determined
using the following F-test.
Where n is the number of data points, R22 is the larger R2, R12 is the smaller R2, K2 is the number of
predictions from the larger R2, and K1 is the number of predictions from the smaller R2.
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RESULTS
The results of the two x three repeated measures ANOVA indicated no significant interaction (P>0.05;
partial η2 = 0.070) (Figure 1). There were, however, significant main effects for time (P<0.05; partial η2
= 0.740) and type of muscle action (P<0.05; partial η2 = 0.850). The follow-up paired t tests for the
marginal means for time (collapsed across type of muscle action) indicated that the pre-test torque
(mean ± SD of CON, ECC, and ISO = 46.5 ± 18.8 Nm) was significantly greater than the post-test
(mean = 33.0 ± 12.8 Nm) (Figure 1). In addition, the marginal means for the types of muscle actions
(collapsed across time) indicated significant differences among the types of muscle action (ECC =
54.5 ± 20.3 Nm > ISO = 40.5 ± 17.5 Nm > CON = 24.2 ± 9.5 Nm). The mean % declines in torque for
pre-test versus post-test were 38 ± 17, 24 ± 12, and 28 ± 9%, for the CON, ECC, and ISO muscle
actions, respectively (Table 1). The results of the polynomial regression analyses indicated that 50%
of the subjects (n = 8) demonstrated quadratic relationships (R2 = 0.61 – 0.96), 44% (n = 7)
demonstrated cubic relationships (R2 = 0.56 – 0.96), and 6% (n = 1) demonstrated a linear (r = 0.28)
relationship between torque and repetition number (Table 1). In addition, the composite relationship
between torque and repetition number was cubic (R2 = 0.98) (Figure 2).
Table 1. Individual Patterns of Response during the Fatiguing Concentric, Isokinetic Protocol.
Subject
Pattern of Response
Cubic
Coefficient of
Determination
R2 = 0.92
Concentric %
Decline
22
1
Eccentric %
Decline
19
Isometric %
Decline
20
2
Cubic
R2 = 0.69
32
7
14
3
Quadratic
R2 = 0.84
6
26
22
4
Quadratic
R2 = 0.90
63
35
33
5
Linear
R2 = 0.28
26
24
21
6
Cubic
R2 = 0.56
59
35
39
7
Quadratic
R2 = 0.88
34
15
37
8
Quadratic
R2 = 0.61
21
21
13
9
Quadratic
R2 = 0.96
38
27
17
10
Cubic
R2 = 0.96
47
18
36
11
Quadratic
R2 = 0.85
50
6
20
12
Cubic
R2 = 0.56
37
13
28
13
Quadratic
R2 = 0.72
44
53
46
14
Cubic
R2 = 0.95
44
16
30
15
Quadratic
R2 = 0.72
4
7
32
16
Cubic
R2 = 0.95
52
32
24
Mean
38
24
28
SD
17
12
9
14
Figure 1. Torque values for concentric, eccentric, and isometric muscle actions, as well as marginal means
(concentric, eccentric, and isometric), prior to (pre-test) and following (post-test) the 50 maximal, concentric
isokinetic forearm flexion muscle actions.
Peak Torque (Nm)
90
80
70
60
50
40
30
20
10
0
pre - test
post - test
Concentric
Eccentric
Isometric
Marginal
Means
Muscle Actions of the Forearm Flexors
Figure 2. Composite pattern of response during the concentric, isokinetic fatiguing protocol (n = 16).
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DISCUSSION
In the present investigation, there was a cubic pattern (R2 = 0.98) for the composite torque versus
repetition number relationship (Figure 2) across the 50 CON forearm flexion muscle actions. Recent
investigations (3,6,10,18) that have characterized the fatigue-related patterns for CON torque of the
leg extensors have reported cubic (R2 = 0.97), quadratic (R2 = 0.86), and linear (r2 = 0.71 – 0.85)
relationships. The general patterns for the composite and individual torque versus repetition number
relationships involved a curvilinear decrease in torque across the repeated muscle actions that
reached a plateau after approximately 30 to 35 repetitions. For the quadratic individual relationships
(n = 8), the highest torque values occurred between the 1st and 3rd repetitions. For the cubic
individual relationships (n = 7), however, the highest torque values were found between the 1st and
7th repetitions. Thus, the differences in the patterns between the cubic and quadratic relationships
were likely due to where the highest torque value occurred.
The 38% decline in CON torque as a result of the 50 CON forearm flexion muscle actions in the
present study was greater than the 26% decline of Beck et al. (3), but less than the 50 and 70%
declines of Beck et al. (2) and Linnamo et al. (14), respectively. The current findings, together with
those of previous investigations (2,3,14) suggest that the difference in the velocities of the fatiguing
muscle actions (30 - 180°·s-1) as well as the number of repetitions (50 to 100) affected the % decline
in CON torque following fatiguing workbouts of the forearm flexors. The differences in % decline
among studies (26-70%) may also have been due to when the torque values were measured. For
example, Beck et al. (2) calculated % decline from the difference between the highest and lowest
torque values during the fatiguing workbouts. In the present study and in Beck et al. (3) and Linnamo
et al. (14), however, % decline was calculated from torque values measured prior to and following the
fatiguing workbouts. Hence, in the present study, there was ~30-45 sec between the end of the
fatiguing workbout and the end of the post-testing that was not included in the study of Beck et al. (2).
This time period likely contributed to a partial recovery in strength and lower % decline.
The results of the present study indicate that torque declined by a mean of 30% for the CON, ECC,
and ISO muscle actions as a result of the 50 CON forearm flexion muscle actions. These findings are
consistent with Beck et al. (3) who reported a 26% decline in the mean of CON, ECC, and ISO
torque after 6 sets of 10 forearm flexion muscle actions at 30°·s -1. Thus, both the current findings and
Beck et al. (3) suggest that the same mechanism of fatigue may be responsible for declines in CON,
ECC, and ISO torque following a fatiguing, CON workbout. Beck et al. (3) hypothesized that the
fatigue-induced declines in torque as well as EMG amplitude may have been due to the decrease in
muscle activation caused by the increase in muscle temperature. However, most previous studies
(1,9,17,21,23,24) have reported declines in torque, but no changes in EMG amplitude as a result of
fatiguing, CON isokinetic muscle actions. Furthermore, it is unlikely that the fatiguing workbout in the
present study increased muscle temperature sufficiently to decrease EMG amplitude and muscle
activation. For example, the 4% decrease in EMG amplitude found by Petrofsky et al. (19) during
cycle ergometry was associated with a 5°C (34 - 39°C) increase in muscle temperature. Edwards et
al. (12), however, reported that intramuscular temperature increased by only 0.4°C per minute during
a maximal ISO contraction. Hence, it is not likely that the time required (<1 min) to complete the
fatiguing workbout in the present study resulted in an increase in intramuscular temperature that
affected muscle activation.
It is possible that the decline in torque in the present investigation was due to a fatigue-induced buildup of metabolic byproducts such as ammonia, hydrogen ions, potassium, and inorganic phosphate
(6,8,11,12). For example, Crenshaw et al. (8) reported that 40 maximal, CON isokinetic muscle
actions at 90°·s-1 resulted in increased intramuscular fluid content and pressure, compression of the
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vascular beds, accumulation of metabolic byproducts, and a decline in torque. Future studies should
examine each of these parameters to specifically identify which may be responsible for the fatigueinduced decline in torque following repeated maximal CON muscle actions.
CONCLUSIONS
There was a cubic pattern for the composite torque versus the repetition number relationship in the
present study. For the individual relationships, however, there were cubic (n = 7), quadratic (n = 8),
and linear (n = 1) patterns of responses. The mean % declines in CON, ECC, and ISO torque as a
result of the 50 CON forearm flexion muscle actions were 38, 24, and 28%, respectively. There were
no differences in mean % declines among the three types of muscle actions (CON, ECC, and ISO).
These findings suggest that the fatiguing CON workbout may have resulted in the build-up of
metabolic byproducts that may have caused the similar declines in torque for the CON, ECC, and ISO
muscle actions.
Address for correspondence: Lewis, Jr. RW, Department of Nutrition and Health Sciences,
University of Nebraska-Lincoln, NE, United States, 68503-0806. Phone: (402) 472-2690; Fax: (402)
472-0522; Email: [email protected]
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