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Article
Effects of Short-Term Dynamic Constant External
Resistance Training and Subsequent Detraining on
Strength of the Trained and Untrained Limbs:
A Randomized Trial
Pablo B. Costa 1, *, Trent J. Herda 2, †, Ashley A. Herda 2 ,† and Joel T. Cramer 3
1Exercise Physiology Laboratory, Department of Kinesiology, California State University, Fullerton,
CA 92831, USA
2Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS 66045, USA;
t.herda@ku.edu (T.J.H.); a.herda@ku.edu (A.A.H.)
3Department of Nutrition and Health Sciences, University of Nebraska—Lincoln, Lincoln, NE 68583, USA;
jcramer@unl.edu
*Correspondence: pcosta@fullerton.edu; Tel.: +1-657-278-4232; Fax: +1-657-278-2103
† These authors contributed equally to this work.
Academic Editor: Eling de Bruin
Received: 14 December 2015; Accepted: 25 January 2016; Published: 27 January 2016
Abstract:
Short-term resistance training has been shown to increase isokinetic muscle strength and
performance after only two to nine days of training. The purpose of this study was to examine the
effects of three days of unilateral dynamic constant external resistance (DCER) training and detraining
on the strength of the trained and untrained legs. Nineteen men were randomly assigned to a DCER
training group or a non-training control group. Subjects visited the laboratory eight times, the first
visit was a familiarization session, the second visit was a pre-training assessment, the subsequent
three visits were for training sessions (if assigned to the training group), and the last three visits were
post-training assessments 1, 2, and 3 (i.e., 48 h, 1 week, and 2 weeks after the final training session).
Strength increased in both trained and untrained limbs from pre- to post-training assessment 1 for
the training group and remained elevated at post-training assessments 2 and 3 (p
ď
0.05). No changes
were observed in the control (p> 0.05). Possible strength gains from short-term resistance training
have important implications in clinical rehabilitation settings, sports injury prevention, as well as
other allied health fields such as physical therapy, occupational therapy, and athletic training.
Keywords:
training-induced; neuromuscular adaptation; isotonic; muscle mechanics; unilateral;
cross education
1. Introduction
Allied health professionals, such as physical therapists, occupational therapists, and athletic
trainers, may benefit from rapid increases in strength of a patient or athlete recovering from injury [
1
–
3
].
In theory, if an individual’s strength can be increased within a short period of time, an alternative to
more expensive and invasive medical procedures may be offered [
1
,
2
]. In addition, they are more likely
to comply with a rehabilitation program and perhaps decrease the risk of reinjury [
3
]. Consequently,
short-term resistance training has been shown to increase isokinetic muscle strength and performance
after only two to nine days of training [
1
,
2
,
4
,
5
]. This short time course for strength adaptations may
conveniently coincide with the commonly limited rehabilitation treatments due to minimal insurance
coverage or lack of compliance [
1
,
2
], or the time demands for return to play in sports. If patients do
not improve quickly, the risk of injury reoccurrence may increase [
1
]. This potential for short-term
Sports 2016,4, 7; doi:10.3390/sports4010007 www.mdpi.com/journal/sports
Sports 2016,4, 7 2 of 10
resistance training to improve muscular performance in a relatively shorter period of time would have
important implications for professionals working in rehabilitation settings [1–3].
Evidence has shown that improvements in muscle performance can be observed in a shorter
period than what is typically used in longer traditional training programs [
1
,
2
,
6
,
7
]. For example,
Prevost et al., (1999) investigated velocity-specific short-term training for two days and reported 22.1%
increases in peak torque (PT) at 270
˝¨
s
´1
after training at 270
˝¨
s
´1
, but no changes for training at
30 and 150
˝¨
s
´1
at the testing velocities of 30 and 150
˝¨
s
´1
[
4
]. Similarly, Coburn et al., (2006) compared
short-term resistance training effects after three sessions of slow- or fast-velocity and found that PT
increased for both training groups [
2
]. However, the slower velocity training group increased PT at
both velocities whereas PT increased only at the faster velocity for the faster velocity training group [
2
].
No changes in PT were observed for the control group and no changes in EMG amplitude were
reported for any of the groups at any of the velocities. The authors concluded three sessions of slow or
fast velocity isokinetic resistance training were sufficient to increase PT and the lack of EMG amplitude
changes suggested increases in leg extension PT were not caused by increases in muscle activation [
2
].
The principle of training called reversibility, or detraining, occurs when a complete cessation or
substantial reduction in training causes a partial or complete reversal of the adaptations induced
by training [
8
,
9
]. Detraining occurs after an individual discontinues a training program [
8
–
15
].
Most of the increases in strength found with resistance training are lost after several weeks of
detraining
[10–14,16,17]
. However, Colliander and Tesch (1992) showed that a resistance training
program incorporating combined concentric and eccentric leg extension exercise retained more of the
novel strength gains than a concentric-only training program [
16
]. In addition, Farthing (2003) found
eccentric muscle action training elicited greater strength gains than concentric training [
18
]. Because
isokinetic muscle actions are typically concentric, it is unknown whether dynamic constant external
resistance (DCER) training, which uses coupled concentric and eccentric muscle actions, and isokinetic
training would affect detraining differently.
Isokinetic muscle actions have been traditionally used in rehabilitation and testing scenarios.
Several studies have examined the effects of isokinetic training on strength and/or muscle
cross-sectional area (CSA) [
1
,
2
,
4
,
5
] and isokinetic training allows development of maximum tension
throughout the range of motion [
7
]. However, DCER training would offer a more accessible, convenient,
cost-effective, and practical method of training, in addition to perhaps providing a greater stimulus to
elicit increases in strength [
19
]. Furthermore, no studies have investigated the effects of short term
resistance training on the contralateral untrained limb or on detraining. Therefore, the purpose of
this study was to examine the effects of three days of DCER training and subsequent detraining on
isokinetic on strength of the trained and untrained contralateral leg extensors during maximal leg
extension muscle actions.
2. Method
2.1. Subjects
Nineteen apparently healthy untrained men (mean
˘
SD age = 21.6
˘
3.4 years; body
mass = 77.9 ˘14.0 kg
;
height = 173.9 ˘4.1 cm
) were randomly assigned to a DCER training group or
control group. Participants were minimally active and naïve to the intent of the study. Individuals
with a history of chronic resistance training (>1 day/week) in the previous 12 months or those who
reported engaging in one or more lower-body resistance training exercise for six months prior to
the start of the study were excluded from participating. Prior to any testing, all subjects read and
signed an informed consent form and completed a health status questionnaire. Individuals with any
degenerative neuromuscular or joint disorders, or who sustained injuries distal to the waist within
six months prior to screening were also excluded from the study. Subjects were asked to maintain their
daily activities, but refrain from any exercise and/or nutritional supplements throughout the course of
the study. Individuals who had been taking nutritional supplements three months prior to screening
Sports 2016,4, 7 3 of 10
were not permitted to participate. This study was approved by the university’s Institutional Review
Board for the Protection of Human Subjects.
2.2. Research Design
A mixed factorial design was used to examine the effects of three days of short-term unilateral
resistance training and subsequent detraining on strength. Subjects visited the laboratory on eight
separate occasions. The first visit was a familiarization session, the second visit was a pre-training
assessment, the subsequent three visits were for training (if assigned to the training group), and the last
three visits were the post-training assessments (i.e., 48 h, 1 week, and 2 weeks after the final training
session). Pre-training assessments were performed 48 h prior to the start of training. Testing included
assessments of DCER strength. The training group performed DCER leg extension exercise with the
dominant leg in each of the three days of training whereas the control group did not take part in the
training intervention. After the three training sessions, post-training assessments were performed in
an identical manner to the pre-training assessments. In order to examine the time course of the effects
of training, post-training assessments were performed 48 h, 1 week, and 2 weeks after the final training
session. All pre- and post-training assessments were conducted at approximately the same time of day.
2.3. Dynamic Constant External Resistance Assessments
The maximal strength of the leg extensors were assessed using a DCER Nautilus leg extension
machine (Nautilus, Inc., Vancouver, WA, USA). The input axis of the machine was aligned with the
axis of rotation of the knee. The distal anterior portion of the leg superior to the ankle was used
as the load bearing point. Three submaximal warm-up sets of increasing tester-selected intensities
(i.e., 6–8, 3–5, and 1–2 repetitions) preceded the maximal strength attempt. When one attempt was
successful, the load was increased by 2–5 kg until a failed repetition occurred. A failed repetition was
defined as the inability to complete the full range of motion with the assigned load. During the tests,
loud verbal encouragement was provided by the investigator. Each subject was instructed to provide
maximal effort throughout the entire range of motion. The greatest load moved through a complete
leg extension range of motion was considered the one repetition maximum (1-RM). A 1-min rest was
allowed between each successive attempt [20,21].
2.4. Dynamic Constant External Resistance Training Protocol
After a rest period of 48 h following the pre-training assessment, the training group took part
in three DCER training sessions separated by 48 h. Participants in the training group performed
4 sets of 10 repetitions. Each training session began with ten warm-up repetitions at approximately
25% of the resistance used for the DCER training session. Approximately 80% of the 1-RM obtained
during the DCER maximal strength assessment was used as the starting load for the DCER group.
A 2-min rest period was allowed between each training set. Training load for the DCER group was
continually increased and adjusted by approximately 1.14 kg as each participant was able to tolerate
a given load with ease in order to ensure that the subject reached failure at approximately the 10th
repetition. All participants taking part in the DCER training intervention were supervised during all
training sessions.
2.5. Rating of Perceived Exertion
Rating of perceived exertion (RPE) was used to compare effort among the DCER training days
and sets [
22
–
26
]. Prior to the start of the study, subjects received instructions on how to use the RPE
scale to rate their perceived exertion. A Category-Ratio scale (CR-10) was used, where “0” is classified
as rest (no effort) and “10” is classified as maximal effort (most stressful exercise ever performed).
The CR-10 has been slightly modified to reflect American English (e.g., easy and hard instead of light
and strong, respectively) [
24
]. Subjects were asked to provide a number on the scale to rate their
overall effort immediately after each set was completed and after the entire training session. The RPE
Sports 2016,4, 7 4 of 10
assessments were conducted during each session by showing the scale and asking subjects “How
would you rate your effort?” and “How would you rate your entire workout?” immediately after each
set of training and after each training session, respectively. Therefore, in this study, “set RPE” was
defined as the RPE reported by the subject after each set, while “session RPE” was defined as the RPE
reported each day after the training session was completed.
2.6. Statistical Analyses
A three-way mixed factorial ANOVA (time (pre- vs. post-training assessment 1 vs. post-training
assessment 2 vs. post-training assessment 3)
ˆ
group (DCER vs. control)
ˆ
limb (trained vs. untrained)
was used to analyze the 1-RM data. A two-way repeated measured ANOVA (time [training session 1 vs.
training session 2 vs. training session 3)
ˆ
set (1 vs. 2vs. 3vs. 4)) was used to analyze RPE assessed
after each set during training. A one-way repeated measures ANOVA (time (training session 1 vs.
training session 2 vs. training session 3)) was used to analyze training session RPE. When appropriate,
follow-up analyses were performed using lower-order two- and one-way repeated measured ANOVAs,
and paired sample t-tests. An alpha level of p
ď
0.05 was considered statistically significant for all
comparisons. Predictive Analytics SoftWare (PASW) version 18.0.0 (SPSS Inc., Chicago, IL, USA) was
used for all statistical analyses.
3. Results
3.1. Dynamic Constant External Resistance Assessments
Table 1contains the means (
˘
SE) for 1-RM strength in the trained and untrained leg. There was
no three-way interaction for time
ˆ
group
ˆ
limb (p= 0.11). However, there was a significant
two-way interaction for time
ˆ
group (p= 0.001). Post-hoc pairwise comparisons for the marginal
means indicated that 1-RM increased in both trained and untrained limbs from pre- to post-training
assessment 1 for the DCER group (p< 0.001) (Figure 1). There were no differences in 1-RM strength
for the DCER group among post-training assessments 1, 2, and 3 (p> 0.05) (Figure 2). No significant
changes were found for the control group (p> 0.05).
Table 1. Means (˘SE) for leg extension 1-RM.
Group Pre-Training
Assessment 1
Post-Training
Assessment 1
Post-Training
Assessment 2
Post-Training
Assessment 3
1-RM (kg)
DCER
(n= 10)
Trained 43.0 ˘3.0 52.6 ˘3.8 * 50.5 ˘3.5 * 50.2 ˘3.2 *
Untrained 41.9 ˘2.7 48.9 ˘4.2 * 48.9 ˘3.8 * 48.6 ˘3.5 *
CONT
(n= 9)
Trained 41.7 ˘2.2 41.9 ˘2.1 41.8 ˘1.9 42.7 ˘1.6
Untrained 41.9 ˘2.1 41.8 ˘1.9 41.7 ˘2.0 42.2 ˘1.7
Notes: 1-RM = 1 repetition maximum; DCER = dynamic constant external resistance; CONT = control. * Denotes
significant change from pre- to post-assessments.
3.2. Rating of Perceived Exertion
Table 2contains the means (
˘
SE) for set and session RPE from the training group. There was
no two-way interaction for time
ˆ
set for set RPE (p= 0.41). However, there was a significant main
effect for set (p< 0.001). Post-hoc pairwise comparisons for the marginal means (collapsed across time)
indicated a significant main effect for set RPE (p< 0.05). RPE increased significantly from the first until
the last set within each session (p< 0.05). For session RPE, there was no main effect for time (p= 0.55).
Sports 2016,4, 7 5 of 10
Sports2016,4,75of10
Figure1.Meansofpercentchangeforlegextension1‐RMforthetrained(A)anduntrained(B)legs.
*Denotessignificantdifferencefromthepre‐testfortheDCERgroup.DCER=dynamicconstant
externalresistance;CONT=control.
Figure2.Means(±SE)forlegextension1‐RMcollapsedacrosslimb.*Denotessignificantdifference
fromthepre‐testfortheDCERgroup.DCER=dynamicconstantexternalresistance;CONT=control.
Figure 1.
Means of percent change for leg extension 1-RM for the trained (
A
) and untrained (
B
) legs.
* Denotes significant difference from the pre-test for the DCER group. DCER = dynamic constant
external resistance; CONT = control.
Sports2016,4,75of10
Figure1.Meansofpercentchangeforlegextension1‐RMforthetrained(A)anduntrained(B)legs.
*Denotessignificantdifferencefromthepre‐testfortheDCERgroup.DCER=dynamicconstant
externalresistance;CONT=control.
Figure2.Means(±SE)forlegextension1‐RMcollapsedacrosslimb.*Denotessignificantdifference
fromthepre‐testfortheDCERgroup.DCER=dynamicconstantexternalresistance;CONT=control.
Figure 2.
Means (
˘
SE) for leg extension 1-RM collapsed across limb. * Denotes significant difference
from the pre-test for the DCER group. DCER = dynamic constant external resistance; CONT = control.
Sports 2016,4, 7 6 of 10
Table 2. Means (˘SE) for set and session rating of perceived exertion for the DCER group.
Training Session 1st Set 2nd Set 3rd Set 4th Set Session
Session 1 6.4 ˘0.54 7.3 ˘0.63 * 8.3 ˘0.45 * 8.6 ˘0.37 * 7.6 ˘0.48
Session 2 5.4 ˘0.37 6.9 ˘0.31 * 7.8 ˘0.29 * 8.6 ˘0.43 * 7.1 ˘0.35
Session 3 5.8 ˘0.33 6.9 ˘0.43 * 7.9 ˘0.50 * 8.5 ˘0.48 * 7.5 ˘0.40
Notes: DCER = dynamic constant external resistance. * Denotes significant change over sets within each
training session.
4. Discussion
Perhaps the most important finding of the present study was the increase in DCER strength
acquired by the training group. DCER strength increased from pre- to post-training assessment 1
in the trained and untrained legs for the DCER training group and remained elevated during
post-training assessments 2 and 3. To our knowledge, this was the first study to report DCER
strength gains with short-term resistance training while also considering the detraining period of two
weeks. These findings are in agreement with previous studies reporting PT increases after short-term
isokinetic training [
1
,
2
]. In addition, the DCER group retained the strength gains during post-training
assessments 2 and 3. That is, DCER strength remained elevated over a two-week period. Typical
increases in strength obtained in longer resistance training programs are diminished after several
weeks of detraining [
10
–
14
,
16
]. Colliander and Tesch (1992) compared the effects of resistance training
and detraining using concentric-only and combined concentric and eccentric muscle actions of the leg
extensors and reported that the group performing coupled concentric and eccentric muscle actions
had a greater overall increase in PT after training and detraining than the concentric-only group [
16
].
These authors suggested strength decreases observed during detraining are not likely due to atrophy,
but perhaps a reduction in neural drive or motor unit activation and hypothesized eccentric muscle
actions are capable of inducing greater motor unit activation than concentric muscle actions [
16
].
Thus, it was suggested a resistance training program incorporating combined concentric and eccentric
repetitions of leg extension can retain more of the obtained strength gains than the training program
with concentric-only repetitions [
16
]. Likewise, Farthing (2003) found eccentric-only muscle action
training elicited greater strength gains than concentric-only training [
18
]. Similarly, Knight et al., (2001)
suggested that isotonic muscle actions may be more effective at increasing torque because isokinetic
resistance is accommodating, hence, it decreases with fatigue [
19
]. These findings [
16
,
18
,
19
], along
with the findings of the current study may indicate an advantage of DCER over isokinetic resistance
training programs when conducted over a relatively short period of time.
For the DCER training group, despite training only one leg, strength increased on the contralateral
limb and was maintained over the two-week detraining period. Unilateral resistance training of a limb
can increase the strength of the contralateral limb through a concept termed cross-education [
27
].
Increases in strength of the contralateral, untrained limb, have been extensively reported in the
literature [
27
,
28
]. Possibly an important finding of the current study is that short-term resistance
training also elicited the cross-education effect. This has important implications for injury rehabilitation,
where in the initial period post-injury strength gains on an injured limb can conceivably be obtained
with short-term contralateral resistance training. Contralateral strength gains have been hypothesized
to be attributed to central neural adaptations (i.e., excitation of the cortex), increased motoneuron
output, and improved postural stabilization [
27
–
29
]. Accordingly, structural changes in the brain
have been reported after only four weeks of unilateral resistance training concomitant with strength
increases in trained and untrained limb [
30
]. In fact, strength gains may not be restricted to the
contralateral untrained muscle, but might be observed in the contralateral untrained antagonist
muscle [
31
]. Therefore, future studies should investigate the effects of short-term resistance training
on contralateral antagonist muscles.
Sports 2016,4, 7 7 of 10
Strength gains were also maintained during the two-week detraining period in the DCER group.
Although in the present study subjects were untrained, these findings were similar to those of
Hortobagyi et al., (1993), who found that two weeks of detraining of resistance-trained athletes
did not cause a significant decrease in maximal bench press, squat, isometric, or concentric isokinetic
strength [
32
]. Similarly, Shaver (1975) reported that recently acquired strength can be maintained in
both trained and untrained limb for up to one week [
33
]. To our knowledge, the current study is
the first to demonstrate short-term increases in strength can be maintained for a two-week period
and in untrained limbs. In contrast, other authors have suggested strength gains that have been
recently acquired may diminish faster than in strength-trained athletes [
9
,
33
]. Thus, the experience
with resistance training (novice vs. well-trained athletes) should be considered when interpreting the
results of a short-term resistance training program and its potential lasting effects.
The neuromuscular system undergoes numerous adaptations following a resistance training
program [
6
,
7
,
34
–
38
]. Short-term resistance training has been shown to increase muscle strength and
isokinetic performance after only a few days of training. Increases in muscular strength following
a resistance training program can be attributed to neural and hypertrophic factors [
6
,
34
–
37
,
39
].
Therefore, voluntary strength increases due to not only the CSA and quality of muscle mass but also
to the extent in which the muscle mass is able to activate [
39
]. In general, neural factors are believed
to account for most of the increases in strength in the early stages of a resistance training program,
whereas hypertrophic factors gradually become prevalent after several weeks of training [
6
,
36
,
38
–
42
].
Research suggests early adaptations to resistance training programs are related to improvements in
neuromuscular efficiency, which perhaps indicates an increased capacity to activate skeletal muscle
voluntarily [
1
,
2
,
4
,
7
,
42
]. Hence, initial improvements in strength and muscular performance reported
following short-term resistance training are generally attributed to neural adaptations rather than
muscle fiber hypertrophy [
6
,
7
]. However, the specific mechanisms of such adaptations in short-term
training are not fully understood [
2
]. For example, Akima et al., (1999) reported increases in PT after two
weeks of resistance training but no changes in muscle CSA or fiber area suggesting strength increases
occurred without muscle hypertrophy [
7
]. Similarly, Prevost et al., (1999) reported velocity-specific
increases in PT training at 270
˝¨
s
´1
after increases in PT after two days of isokinetic training but not
with training at 30 and 150
˝¨
s
´1
[
4
]. Because improvements were only seen in one velocity, and muscle
hypertrophy would most likely yield strength increases at the other velocities, investigators suggested
that neural adaptations play a major role in strength improvements which are specific to a training
velocity [
4
]. Beck et al., (2007) suggested that responses to training might be influenced by the number
of training sessions, training volume, and muscle(s) being tested [
3
]. Nevertheless, Akima et al., (1999)
and Costa et al., (2013) suggested future studies should investigate the precise mechanisms underlying
strength gains obtained with short-term resistance training [7,43].
The results revealed there were no differences in RPE as acknowledged by the subjects among the
DCER training sessions. However, RPE increased from the first to the fourth set within each training
session. These results are similar to those found by Egan et al., (2006), who reported mean session RPE
values of 7.3 for six sets of six repetitions of traditional resistance training using squats at an intensity
of 80% of 1-RM [
22
]. Likewise, Sweet et al., (2004) reported mean RPE values between 6.8 and 8.2 for
70 and 90% of leg press 1-RM, respectively [
23
]. Thus, perceived effort from a short-term resistance
training program in the current study was similar to previous studies and was not lower because of
the shorter training program duration.
5. Conclusions
The primary finding of this study was that DCER strength increased in the trained and untrained
limbs with three days of contralateral training. This has important implications for injury rehabilitation,
where in the initial period post-injury, strength gains on an injured limb can possibly be obtained
with short-term resistance training. Furthermore, research has shown the feasibility and benefits
of preoperative resistance training prior to surgical intervention to decrease the odds of inpatient
Sports 2016,4, 7 8 of 10
rehabilitation, reduce the length of hospital stay, and promote overall postoperative recovery [
44
–
47
].
It is believed the increases were due to an unidentified factor because of strength gains observed
in the untrained limb after DCER resistance training. Future studies should investigate the precise
physiological components responsible for short-term contralateral strength gains. The findings of
the current study may indicate an advantage of DCER over isokinetic resistance training programs
when conducted over a relatively short period of time. These findings have important implications in
clinical rehabilitation settings, sports injury prevention, as well as in other allied health fields such
as physical therapy, occupational therapy, and athletic training. To our knowledge, the current study
is the first to demonstrate recently-acquired strength can be maintained for a two-week period in
untrained limbs. Therefore, future studies should examine the effects of short-term resistance training
on injury prevention and rehabilitation.
Author Contributions:
Pablo B. Costa was involved in the study concept and design, and was the primary
manuscript writer, and carried out data acquisition, data analysis, and data interpretation. Trent J. Herda and
Ashley A. Herda were significant contributors to data acquisition, read and approved the final manuscript, and
were manuscript reviewers/revisers. Joel T. Cramer was the primary manuscript reviewer/reviser, a substantial
contributor to concept and design, contributed to data analysis and interpretation, and was involved in
manuscript revision.
Conflicts of Interest: The authors declare no conflict of interest.
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