Content uploaded by Clementine Grandou
Author content
All content in this area was uploaded by Clementine Grandou on Dec 11, 2019
Content may be subject to copyright.
Vol.:(0123456789)
Sports Medicine
https://doi.org/10.1007/s40279-019-01242-2
SYSTEMATIC REVIEW
Overtraining inResistance Exercise: AnExploratory Systematic Review
andMethodological Appraisal oftheLiterature
ClementineGrandou1 · LeeWallace1· FrancoM.Impellizzeri1· NicholasG.Allen1· AaronJ.Coutts1
© Springer Nature Switzerland AG 2019
Abstract
Background The balance between training stress and recovery is important for inducing adaptations to improve athletic per-
formance. However, continuously high training loads with insufficient recovery may cause fatigue to accumulate and result
in overtraining. A comprehensive systematic review is required to collate overtraining literature and improve the current
understanding of the mechanisms underlying functional overreaching (FOR), non-functional overreaching (NFOR) and the
overtraining syndrome (OTS) in resistance training.
Objective The objective of this systematic review was to establish markers of overtraining and elucidate the mechanisms
underlying maladaptive resistance training conditions. Furthermore, this review aims to critically evaluate the methodologi-
cal approaches of the overtraining literature.
Methods A systematic literature search was performed on PubMed, Web of Science and SPORTDiscus to identify studies up
to June 2019. Electronic databases were searched using terms related to resistance training and overtraining. Records were
included if they attempted to induce a state of overreaching or overtraining through resistance exercise in healthy participants.
Results A total of 22 studies were selected for review. Among these studies, eight resulted in decrements in performance and
measured changes in performance during a follow-up period. There were four studies that reported decrease in performance
yet failed to implement follow-up measures. A total of 10 studies reported no decline in performance. Overall, a lack of
standardisation in methodology (follow-up performance testing) and diagnostic criteria prevents consistent determination
of FOR, NFOR and OTS in resistance training.
Conclusions Few studies have appropriately established FOR, NFOR or OTS in resistance training. Overtraining may be
related to frequent high-intensity and monotonous resistance training. However, no marker other than a sustained decrease
in performance has been established as a reliable indicator of overtraining in resistance exercise.
Registration This systematic review was registered on the Open Science Framework (https ://osf.io/) (https ://doi.org/10.17605
/osf.io/5bmsp ).
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s4027 9-019-01242 -2) contains
supplementary material, which is available to authorized users.
* Clementine Grandou
Clementine.Grandou@uts.edu.au
1 Human Performance Research Centre, University
ofTechnology Sydney, Sydney, Australia
1 Introduction
Many athletes perform resistance exercise or strength train-
ing as a means to improve athletic performance. Resistance
training programs can be systematically manipulated through
changes in training variables (i.e. intensity, volume, exercise
selection and sequence, rest intervals, repetition velocity and
training frequency) to elicit a specific response (i.e. muscular
strength, hypertrophy, endurance, motor performance, bal-
ance or coordination) [1, 2]. Strenuous resistance training
loads should be applied to obtain high-level performance
in strength and power-based sports [2]. The physical per-
formance of an athlete undertaking resistance training may
be influenced by their ability to adapt to increasing training
loads. Consequently, athletes and coaches are continually
challenged to find the optimal balance between training and
recovery to enhance athletic performance. A disruption in
this balance may result in impaired performance [3, 4].
During a typical training cycle, athletes often undergo
periods of overload and recovery in an attempt to optimise
physical performance. The process of overload is achieved
through an increase in training load [3]. Acute fatigue
occurs following overload training which may result in a
C.Grandou et al.
Key Points
Failure to demonstrate decreases in performance and
inadequate performance testing during a follow-up
period prohibit the diagnosis of FOR, NFOR or OTS in
the majority of studies.
Early studies show that frequent and monotonous resist-
ance training performed at high intensity may increase
susceptibility to training maladaptation.
The mechanisms that underlie overtraining in resistance
exercise remain unclear. Coaches and athletes must con-
tinue to rely on training-specific performance decrements
to determine FOR, NFOR or OTS.
longer-term decrements in performance with or without
a range of other symptoms (e.g. hormonal dysregulation,
psychological disturbances, reduced immune function, sleep
disorders) that require ‘weeks-months’ and ‘months-…’ to
recover, respectively [7]. Consequently, the correct diagnosis
requires maximal performance testing and can only be made
retrospectively. Importantly, the OTS is characterised by an
unexplained decline in performance and depends on a wide
variety of training and contextual factors. Therefore, the cor-
rect diagnosis of OTS should also be based on the exclusion
of confounding factors/disorders (e.g. viral disorder, bacte-
rial infection and other physical diseases) [7]. The amount
that performance must deteriorate before FOR, NFOR or
OTS is diagnosed has been debated in the literature. The
magnitude of performance decline required to diagnose
FOR, NFOR or OTS may vary widely depending on the
specific performance assessment and the training status of
the athlete. Despite the fact that a meaningful decrease in
sport-specific performance is individual, for the purpose of
this review, a statistically significant decline in performance
was necessary to indicate a state of possible FOR, NFOR
or OTS.
The majority of previous overreaching/overtraining inves-
tigations have been conducted in endurance activities [7].
However, previous authors have proposed that overtrain-
ing in resistance exercise can elicit considerably different
biological responses when compared to overtraining with
endurance activities [8, 9]. The mechanisms behind these
contrasting responses have not been established. Accord-
ingly, there is a need to investigate overtraining respective to
the training mode. It has also been suggested that the aetiol-
ogy of resistance exercise overtraining differs with regard
to whether training volume or intensity is manipulated/
increased [7]. However, the mechanisms and manifestation
of FOR, NFOR and OTS through resistance exercise remain
relatively unknown.
Overtraining has been suggested to be a significant prob-
lem for strength or power athletes who undertake primar-
ily resistance training [8]. Determining the point at which
training becomes maladaptive continues to challenge both
athletes and coaches in their attempts to achieve optimal
performance. At present, there is no systematic review of
the studies that have examined NFOR, FOR or OTS in
resistance-trained athletes. Therefore, the purpose of this
systematic review was to critique and appraise the results
and methodology of studies that have attempted to induce
FOR, NFOR or OTS through resistance exercise in healthy
adults. Additionally, the present review aims to elucidate the
physiological alterations and potential mechanisms of over-
training, as well as determine if any markers (performance,
biochemical, physiological or psychological) may be used to
monitor FOR, NFOR or OTS in resistance training.
temporary performance decrement [5]. When adequate rest
is prescribed, the resultant acute fatigue may be followed
by a positive adaptation or improvement in performance
[3]. This process is referred to as functional overreaching
(FOR). It is well established that periods of physiological
stress are required to stimulate the adaptations responsible
for enhancing performance [3]. Accordingly, coaches and
athletes often induce FOR as part of a training program to
elicit a supercompensation effect. However, continuously
high training loads with insufficient recovery may cause
fatigue to accumulate and result in long-term reductions in
performance capacity. This maladaptation to training can
manifest as a state of non-functional overreaching (NFOR)
and, in extreme and prolonged cases, may develop into the
overtraining syndrome (OTS).
Many previous studies have investigated the mechanisms
of overtraining in an attempt to establish indicators of over-
training through the use of various performance, biochemi-
cal, physiological and psychological parameters (for review,
see Halson etal. [6] and Meeusen et al. [7]). However,
despite many attempts, no clear guidelines or diagnostic
tools other than a sustained decrease in performance have
emerged for the monitoring and detection of FOR, NFOR or
OTS in resistance exercise [7]. This may be due to the varied
terminology used by previous studies or the difficulty that
lies in differentiating between these conditions. This review
follows the well-accepted definitions proposed by Meeusen
etal. [7], where FOR, NFOR and OTS are differentiated by
the length of time required for recovery. FOR is defined as
a short-term decrement in performance without severe psy-
chological or other lasting negative symptoms that requires
‘days-weeks’ to recover. FOR is followed by a subsequent
supercompensation effect where performance is improved.
NFOR and OTS are caused by overtraining and defined as
Overtraining in Resistance Exercise…
2 Methods
This review was conducted according to PRISMA (Preferred
Reporting Items for Systematic Reviews and Meta-Analyses)
guidelines [10]. A systematic review protocol that included
the review question, search strategy, exclusion criteria and
risk of bias assessment was registered with the Open Science
Framework (10.17,605/OSF.IO/5BMSP; 11 January 2019).
2.1 Eligibility Criteria
Eligibility criteria were drafted and subsequently refined
by three authors (CG, LW, FI) using a random sample of
studies. Included studies met the following study crite-
ria [population, intervention, comparator, outcome, study
design (PICOS)] and report characteristics. P: Participants
with chronic diseases, metabolic disorders or musculoskel-
etal injuries were excluded. Studies were considered eligi-
ble if they included an intervention aimed to induce FOR,
NFOR or OTS through resistance training. I: Interventions
were included regardless of whether or not they were able to
induce a decrement in performance which is essential for the
diagnosis of FOR, NFOR or OTS. Studies involving an acute
bout of intensified training (i.e. increased training load) were
not eligible for inclusion in this review unless the authors
stated that they were attempting to overreach or overtrain
participants. Interventions combining resistance training
and aerobic training were excluded to account for a possible
interference effect. Supplementation studies were eligible
for inclusion if the data provided for non-supplemented par-
ticipants were reported separately. C: All comparators and
control conditions were eligible for this review. O: Changes
in physical performance following the overtraining period
and follow-up were the primary outcome measure of this
review. Secondary outcome measures included biochemical,
neuro-muscular, psychological and morphologic effects. S:
This review considered randomised controlled trials (RCTs),
non-randomised controlled trials (NRCTs), uncontrolled tri-
als (UCTs) and grey literature to ensure literature saturation.
2.2 Search
A literature search was conducted by one author (CG) in
the following electronic databases: PubMed, Web of Sci-
ence Core Collection and SPORTDiscus. Databases were
searched from inception up until June 2019. No language or
publication status restrictions were imposed on the search to
ensure literature saturation. The following Boolean search
string was used on all databases: (resistance training OR
resistance exercise OR strength training OR strength exer-
cise OR weight training OR weight exercise OR weight
lifting OR weightlifting) AND (overtrain* OR over-train*
OR overreach* OR over-reach* OR fatigue OR underper-
formance OR underperformance OR under performance OR
underrecovery OR under-recovery OR under recovery). A
comprehensive search strategy is provided in TableS1. Trial/
study registries were searched during a pilot phase; how-
ever, due to the non-clinical nature of this review no results
were found. In conjunction with the database searches, the
reference lists of relevant studies, reviews and books were
screened for possible omissions.
2.3 Study Selection
Articles retrieved through the systematic search were
exported into a reference management software (EndNote
version X8) and all duplicate articles were removed. All
references were then imported into Covidence (Covidence
Systematic Review Software, Veritas Health Innovation,
2013) for assessment of eligibility. Two authors (CG, NA)
independently screened the records by title and abstract,
with all potentially eligible references proceeding to full-
text screening; conflicts were resolved by a third author (FI).
Two authors (CG, NA) then independently screened the full
text of all included articles against the eligibility criteria.
2.4 Data Extraction
Data were extracted by two authors (CG, LW) and imported
into an Excel spreadsheet that was designed for this review
(TableS2). Information extracted from each eligible study
included publication details (author, year), participant char-
acteristics (sex, training history), study methods (design,
randomisation), overtraining intervention (duration, mode,
frequency, volume, intensity, length of follow-up) and com-
parator. Additionally, pre- and post-intervention values were
extracted for primary (physical performance) and second-
ary (biochemical, physiological and psychological) outcome
measures.
2.5 Risk ofBias Assessment
The results between the groups were not of interest for this
review; rather the pre-to-post changes were required for
assessment of the effects of overtraining. Accordingly, an
assessment of bias was undertaken of relevant methodologi-
cal variables. To comply with the AMSTAR 2 (Assessing
the Methodological Quality of Systematic Reviews), assess-
ment of allocation concealment, blinding of participants and
assessors was conducted for RCTs. Additionally, confound-
ing and selection bias were assessed for NRCTs and UCTs.
Furthermore, risk of bias assessment included a narrative
review of the length of follow-up and frequency of perfor-
mance testing that is required to accurately diagnose a state
C.Grandou et al.
of FOR, NOR or OTS. The proposed methods of assessment
of risk of bias were changed from the review protocol reg-
istered on the Open Science Framework. One author (CG)
piloted the proposed method of using the Cochrane risk of
bias appraisal tool for the included RCTs. However, due
to the nature of this review, the results did not accurately
reflect risk of bias in terms of overtraining methodology. For
example, if the performance of participants was not assessed
during a follow-up period, there would be an inherent risk
of bias within the results as an accurate diagnosis of FOR,
NFOR or OTS cannot be made.
3 Results
3.1 Study Selection
The initial database search yielded 4649 studies. An addi-
tional nine studies were identified through other sources
(searching reference lists and consultation with experts)
(Fig.1). Once duplicates were removed, 2992 titles and
abstracts were screened for inclusion and of those 2923 stud-
ies were excluded based on the eligibility criteria (Sect.2.1).
A total of 69 studies were retrieved as full text and assessed
for eligibility and of those 47 were excluded (TableS3).
The reasons for exclusion at the full text level are displayed
in Fig.1. Upon completion of these procedures, 22 studies
were included for analysis in this systematic review.
3.2 Study Characteristics
Among the 22 included studies, 14 were RCTs, 2 were
NRCTs, and 6 were UCTs. Physical performance of par-
ticipants was measured by 20 of the included studies. Fry
etal. [11, 12] reported on secondary outcomes of a previous
study by the same author which did include physical per-
formance measures [13]. However, these studies are treated
separately throughout this review. At least, one measure of
performance significantly declined following the overload
program of 12 studies (Fig.2) [9, 11–21]. Within the stud-
ies that reported a decline in a measure of physical perfor-
mance, eight included follow-up measures after the overload
training intervention [11–13, 16–20]. No decline in physi-
cal performance was reported in ten of the included stud-
ies [22–31]. Lowery etal. [27] did not presentperformance
data for placebo participantsand therefore was included in
studies that did not induce a decline in performance. Addi-
tionally, authors should exercise caution when interpreting
the results of Lowery etal. [27] and Wilson etal. [31] due
to the controversy surrounding these manuscripts [32]. The
descriptive results of the 12 studies that reported decreases
in performance are displayed in Table1. The descriptive
47 full-text articles excluded:
•Concurrent aerobic exercise (n =15)
•No attempttooverreach/overtrain (n =13)
•No intervention (n = 11)
•Unable to retrieve (n = 4)
•Conference abstract (n = 3)
•Injury (n = 1)
4649 records identified through database
search.
9additional records identified through
other sources
2992 records after duplicates removed
2992 records screened
69 full-text articles assessed for eligibility
2923 records excluded
22 studies included in systematic review
Fig. 1 PRISMA flow diagram of systematic search and included studies
Overtraining in Resistance Exercise…
results of the nine studies that did not adversely affect per-
formance are displayed in the TableS4. Among the 12 stud-
ies that reported decreases in performance, nine reported
on measures of biochemistry [11–13, 15–18, 20, 21], five
studies investigated physiological changes [13, 16, 18–20],
and three studies measured psychological and perceptual
responses [9, 13, 18].
3.3 Performance
Twelve studies demonstrated decreases in at least one meas-
ure of performance following an overload training interven-
tion (Table2). Among these studies, eight implemented
follow-up measures of performance. The majority of studies
reported that performance was restored within the follow-
up period. However, many studies failed to report the time
course changes of performance within the follow-up period
[9, 14, 15, 21]. The most common performance measure
was maximal muscular strength. Six studies demonstrated
significant decreases in strength [11–13, 16–18]. Contrasting
results were found for secondary performance measures. For
example, six studies measured vertical jump performance
[9, 14–16, 18, 21], of these, three resulted in decreased per-
formance [15, 18, 21]. Additionally, two studies reported
decrements in sprint performance [9, 14]. Fry etal. [14]
reported decreases in sprint performance; however, 1RM
strength improved following the training intervention. Other
secondary performance measures included in the analyses
Follow-up measures (n=8)
Duration: >1 month (n=5)
•Fry et al. [13] (survey)
•Fry et al. [12] (survey)
•Fry et al. [11] (survey)
•Fry et al. [16] (interview)
•Margonis et al. [18]
Duration: <1 week (n=1)
•Hecksteden et al. [17]
Decrease in one measure of
physical performance (n=12)
Duration: 1 week –1 month
(n=2)
•Nicoll et al. [19]
•Sterczala et al. [20]
No decrease in any measure
of physical performance
(n=10)
•Fry et al. [24]
•Fahey et al. [22]
•Raastad et al. [28]
•Ratamess et al. [29]
•Fatouros et al. [23]
•Kraemer et al. [26]
•Sweeny et al. [30]
•Wilson et al. [31]
•Hasegawa et al. [25]
•Lowery et al. [27]
Included studies (n=22)
No follow-up measures (n=4)
•Warren et al. [21]
•Fry et al. [15]
•Fry et al. [14]
•Fry et al. [9]
Fig. 2 Flow diagram of performance outcomes and follow-up interventions of included studies
C.Grandou et al.
Table 1 Descriptive results of studies that adversely affected at least one measure of physical performance
Study design Study Subjects Overload training Follow-up
Duration Frequency Volume and intensity
(sets × repetitions)
Mode
Follow-up
RCT Fry etal. [13] 17 resistance trained, men 2weeks OT: 7days/week
C: 1day/week
OT: 10×1 at 100% 1RM
C: 3 ×5 at 50% 1RM
Tru-Squat machine
(upper body resistance
exercise held constant)
Follow up survey (8
weeks)
RCT Fry etal. [12] [13] [13] [13] [13] [13] [13]
RCT Fry etal. [11] [13] [13] [13] [13] [13] [13]
RCT Fry etal. [16] 16 resistance trained, men 2weeks OT: 7days/week
C: 2days/week
OT: 10×1 at 100% 1RM
C: 3×5 @ 50% 1 RM
Tru-Squat machine Follow up interviews
(8weeks)
UCT Margonis etal. [18] 12 recreationally trained,
men
3weeks 6days/week 6 ×1–6 at 85–100% 1RM Bench press, squat,
snatch, hang clean,
deadlift, curl and row
3weeks, 2days/week:
2× 10–12 at 70% 1RM
Then 3weeks rest
UCT Nicoll etal. [19] 14 resistance trained, men
HPOR (n = 6)
HIOT (n = 8)
HPOR:7.5days
HIOT: [16]
HPOR: 2 sessions/day
HIOT: [16]
HPOR: 10×5 at 70%
1RM (maximum con-
centric velocity)
HIOT: [16]
HPOR: barbell back squat
HIOT: [16]
HPOR: 1-week recovery
HIOT: [16]
RCT Sterczala etal. [20] 17 resistance trained, men
AA (n = 8)
Placebo (OT) (n = 3)
Control (n = 6)
1week AA/OT: 15 sessions
C: maintained normal
training schedule
AA/OT: 10×5 at 70% of
the system 1RM mass.
When barbell velocity
dropped below 90% of
the highest value for the
set load was reduced.
C: maintained normal
training schedule
AA/OT: ‘speed’ barbell
back squats
C: maintained normal
training schedule
1week training cessation
UCT Hecksteden etal. [17] 23 strength athletes, men
and women
6days 11 sessions 4×6 at 85% 1RM
Implementing drop sets
to failure and eccentric
overload training
Bench press and squat
(plus variations)
2days rest
No follow-up
UCT Warren etal. [21] 28 elite junior weightlift-
ers
7days 2–3 sessions/day Approximate volume:
90,000kg/week
Intensity: percentage of
the participants best
snatch and best clean
and jerk
Snatch, clean, back squat,
front squat, snatch pull
and clean pull
Overtraining in Resistance Exercise…
Table 1 (continued)
Study design Study Subjects Overload training Follow-up
Duration Frequency Volume and intensity
(sets × repetitions)
Mode
RCT Fry etal. [15] 28 male weightlifters
AA (n = 13)
Placebo (n = 15)
7days 2–3 sessions/day Approximate volume:
90,000kg/day
Intensity: 70–100% 1RM
Multi-joint barbell
exercises: snatch, power
snatch, snatch pull,
clean, power clean,
clean pull, jerk, push
jerk, push press, clean
and jerk, front squat,
back squat
RCT Fry etal. [14] 9 resistance trained, men 3weeks OT: 5days/week
C: 2days/week
OT: 8×1 at 95% 1RM
C: 3×5 at 70% body
weight
Tru-Squat machine
NRCT Fry etal. [9] 6 resistance trained, men 3weeks 3days/week Barbell back squat:
2×1 at 95% 1 RM
3×1 at 90% 1RM
Leg curls:
3×10RM
Barbell back squat and
leg curls
(upper body resistance
exercise held constant)
RCT randomised controlled trial, UCT uncontrolled trial, RM repetition maximum, OT overload training, C control, NR not reported, HMB-FA beta-hydroxy-beta-methylbutyrate-free acid, AA
amino acid, HPOR high power overreaching, HIOT high-intensity overtraining, kg kilogram
C.Grandou et al.
were maximal repetitions until exhaustion [13, 15, 21], Win-
gate power [18], sit and reach [9], and muscular torque [13,
14].
3.4 Biochemistry
Biochemical responses were reported by nine studies that
demonstrated decreases in performance. A variety of blood
and urinary biomarkers including hormones and muscle
damage markers as well as oxidative stress and inflamma-
tory markers were reported. Four studies reported on the
between-group biochemical responses of overload partici-
pants in comparison to a control (Table3). Additionally, nine
studies provided pre- to post-intervention results for over-
load training participants (TableS5). Commonly reported
measures included cortisol [11, 15, 20], testosterone/free
Table 2 Performance results of studies that adversely affected at least one measure of physical performance
RCT randomised controlled trial, NRCT non-randomised controlled trial, UCT uncontrolled trial, HPOR high power overreaching, HIOT high-
intensity overtraining, RM repetition maximum, CMJ countermovement jump
Study Study design Performance post overload training Follow-up
Improved No change Declined
Fry etal. [13] RCT Squat repetitions @ 70%
1RM
1RM squat
Isokinetic leg extension
torque
Follow-up survey indicated
that participants were able
to return to normal training
load with 2–8weeks of
recovery.
Fry etal. [12] RCT [13] [13] [13]
Fry etal. [11] RCT [13] [13] [13]
Fry etal. [16] RCT Vertical jump (CMJ, squat
jump, depth jump)
Mean power, peak velocity
and peak force @ 40,
70% 1RM
1RM squat
Mean power @ 100% 1RM
Follow-up interviews
indicated that participants
were able to return to
normal training load with
2–8weeks of recovery.
Margonis etal. [18] UCT 1RM strength
Vertical jump
Wingate power
1RM strength returned to
baseline values following
3weeks of recovery.
Nicoll etal. [19] UCT HIOT: [16] HPOR: squat mean power
HIOT: [16]
HPOR: muscular power
returned to baseline fol-
lowing 1week of recovery.
HIOT: [16]
Sterczala etal. [20] RCT 1RM back squat
Squat mean power @70%
1RM
Squat mean barbell veloc-
ity @ 70% 1RM
Mean barbell velocity values
returned to baseline fol-
lowing 1week of training
cessation
Hecksteden etal. [17] UCT Squat maximal isometric
contraction
Bench press maximal
isometric contraction
Performance was not
restored to baseline values
following 2days rest
Warren etal. [21] UCT Snatch lift test to exhaus-
tion
Vertical jump
Fry etal. [15] Snatch (repetitions, missed
lifts & successful lifts)
Vertical jump
Fry etal. [14] RCT 1RM squat
Agility run (left)
Isokinetic leg extension
torque
Agility run (right)
Vertical jump (CMJ, non-
CMJ, low depth, high
depth)
Sprint
Fry etal. [9] UCT 1RM squat
Sit and reach
Lower body reaction time
Vertical jump
Back and hip extension
isokinetic peak force
Sprint
Squat isokinetic peak force
Overtraining in Resistance Exercise…
testosterone [11, 15, 20], testosterone:cortisol (T:C) ratio/
free T:C ratio [11, 15, 20], basal growth hormone [11, 15,
17] and exercise induced growth hormone [11, 15], catecho-
lamines [12, 16, 20], creatine kinase (CK) [13, 17] and pre-
and post-exercise blood lactate/lactic acid [12, 13, 15, 21].
In comparison to a control, overload training participants
demonstrated exacerbated responses of cortisol [20], cre-
atine kinase [13] and noradrenaline [12]. Blunted responses
were reported in T:C and free T:C ratio [11] and exercise-
induced lactate concentrations [13].
3.5 Physiology
Amongst the studies that demonstrated declines in perfor-
mance, five measured physiological adaptations. For exam-
ple, Fry etal. [13] reported no significant changes in resting
heart rate upon waking. Decreases in range of motion were
demonstrated following 3weeks of overload resistance train-
ing [18]. Three studies investigated the physiological mecha-
nisms that may underpin the decline in performance charac-
teristic of overtraining [16, 19, 20]. No significant changes
were demonstrated in contractile protein isoform expression
[16, 19]. Fry etal. [16] and Sterczala etal. [20] reported
downregulation of the β2-adrenergic receptor (β2-AR) system
with simultaneous increases in epinephrine:β2-AR density
following overload training. Additionally, Nicoll etal. [19]
reported altered mitogen-activated protein kinase (MAPK)
activity in response to overtraining in resistance exercise.
3.6 Psychological andPerceptual Responses
Psychological and perceptual responses were reported by
three studies that demonstrated declines in performance.
Margonis etal. [18] demonstrated increases in delayed
onset muscle soreness following the increase in training
load. Conflicting results were reported for perceived lower
back pain and knee pain. No increases in pain were reported
where participants trained 3days per week [9]. However,
increases in pain were demonstrated in a study where par-
ticipants trained 7days per week [13]. Fry etal. [13] also
reported decreases in perceived recovery and strength status
following the overload training intervention. However, no
significant changes in sleep pattern (sleep quality and dura-
tion) were reported throughout the trial [13].
3.7 Risk ofBias
The risk of bias assessment results, including selection
bias, performance bias and confounding bias, is available in
Fig.S6. In the case of UCTs, selection bias was assessed as
not applicable as study protocol did not involve allocation
of participants. No studies demonstrated adequate allocation
concealment. Random sequence generation was performed
by one study [31]. Blinding of participants was adequately
performed by seven studies [15, 20, 22, 26–28, 31]. How-
ever, as these studies involved supplementation groups, only
the results of the placebo participants are relevant for discus-
sion in this review. A total of eight studies are reflective of
possible FOR, NFOR or OTS [11–13, 16–20]. These studies
demonstrated an adequate decrease in at least one meas-
ure of performance and included follow-up measures after
the overload period. Of these studies, only one adequately
controlled for nutritional confounders [18]. An additional
bias may exist as the majority of the studies included in this
review came from the same group of authors.
4 Discussion
Despite the fact that many athletes perform resistance-based
exercise as a significant part of their training, much of the
scientific literature on overtraining has focused on endurance
activities [7]. This review analysed changes and attempted
to identify relationships between numerous measures of
performance, biochemistry, physiology and psychology that
occurred in response to FOR, NFOR or OTS in resistance
exercise. This systematic review also aimed to develop an
understanding of the mechanisms and manifestation of over-
training in resistance exercise. Such findings may provide
Table 3 Between-group biochemical responses of overload partici-
pants in comparison to control participant following the completion
of overload training
T:C testosterone:cortisol, β2-AR β2-adrenergic receptor, R resting, EI
exercise induced
Parameter Measure Blunted
response
No signifi-
cant differ-
ence
Elevated
response
Hormones
Cortisol R [20]
Testosterone R [20]
T:C ratio R [11] [20]
EI [11, 20]
Free T:C ratio R [11]
EI [11]
Adrenaline R [12, 20]
EI [12]
Noradrenaline R [12]
EI [12]
Adrenaline: β2-AR
density
R [20]
Blood biomarkers and muscle damage
Lactate R [13]
EI [13]
Creatine kinase R [13]
C.Grandou et al.
an early indication of training maladaptation. However, to
accurately elucidate the effects of overtraining in resistance
exercise, it is important to accurately diagnosis a state of
FOR, NFOR or OTS in intervention participants.
4.1 Summary ofEvidence
4.1.1 Establishing Overreaching/Overtraining
Previous studies have attempted to investigate the time
course changes of training maladaptation in resistance exer-
cise. However, many investigations have failed to appropri-
ately induce and diagnose FOR, NFOR or OTS. Methodo-
logical limitations and contrasting definitions within the
literature contribute to the discrepant findings. At present,
changes in performance and recovery time are required
to diagnose and distinguish between these conditions [7].
Amongst the 22 studies included in this review, only eight
studies reported declines in performance and implemented
follow-up measures. However, few studies used a longitu-
dinal approach to monitor performance during a follow-up/
recovery period. Due to the short duration and lack of per-
formance testing throughout the follow-up period, the time
course changes of performance in much of the resistance
exercise overtraining literature remain unknown. Addition-
ally, many studies that adversely affected performance did
not measure performance during a follow-up period. Whilst
these studies may provide some insight into training mal-
adaptation, it is not possible to determine the prognosis of
training maladaptation if performance is not adequately
monitored throughout a follow-up period.
Many of the previous resistance overtraining interven-
tions failed to adversely affect performance following an
overload training period. Whilst these studies are not reflec-
tive of a state of FOR, NFOR or OTS, many researchers
reported that overreaching or overtraining occurred. For
example, Raastad etal. [28] did not report any decreases
in performance measures (i.e. muscular strength), yet sug-
gested that this should be recognised as overreaching as the
strength gain per workout was reduced. However, a decline
in strength adaptation per training bout may simply reflect
the law of diminishing returns rather than a maladaptation
to training. Future studies should attempt to standardise
methodology (e.g. follow-up period and performance test-
ing) and diagnostic criteria (e.g. demonstrated decrease in
performance lasting ‘days-weeks’ for FOR, ‘weeks-months’
for NFOR and ‘months…’ for OTS) to avoid inappropri-
ate determination of FOR, NFOR and OTS in resistance
training.
4.1.2 Performance
Performance outcomes of resistance training have been
measured using a number of different tests including maxi-
mal muscular strength, muscular torque, force produc-
tion and maximal repetitions until exhaustion [9, 16, 21].
To establish training maladaptation, the performance test
utilised should be a reflection of an athlete’s competition
performance [7]. However, there is a lack of consistency
in performance measures implemented within studies. This
may be due to the diverse nature of resistance training and
the variety of athletic performance outcomes (e.g. maximal
strength, muscular power or hypertrophy). If the perfor-
mance outcome of a resistance-based sport/discipline is not
maximal strength, it is counterintuitive to measure maxi-
mal strength as a primary performance indicator. Therefore,
future studies utilising resistance training must specify a pri-
mary performance test reflective of the demands and envi-
ronmental context of an athlete’s competition performance.
The most common methods for assessing performance in
included studies are maximal muscular strength tests. Maxi-
mal muscular strength tests are a resistance training-specific
tool that can be utilised for the detection of FOR, NFOR or
OTS in resistance exercise. However, maximal strength tests
are exhaustive in nature and may contribute to fatigue levels
which increase the risk of training maladaptation. Few stud-
ies demonstrated decreases in maximal strength. For exam-
ple, Margonis etal. [18] reported significant decreases in
1RM strength which were not restored following a 6-week
taper period. These results suggest that athletes developed
the OTS. Hecksteden etal. [17] reported a significant decline
in maximal isometric force that did not return to normal val-
ues following a recovery period of 2days. However, due to
the short follow-up period the length of recovery required to
distinguish between FOR, NFOR or OTS, correct diagnosis
is not possible. Additional studies that reported decreases in
maximal strength utilised participant interviews and surveys
to monitor the length of recovery required to re-establish
performance [11–13, 16]. Collectively, these studies have
reported attenuated performance which may provide impor-
tant insight into the mechanisms and manifestation of train-
ing maladaptation. However, as these studies did not appro-
priately measure performance during a sufficient follow-up
period it is not possible to determine if these results reflect
FOR, NFOR or OTS. Future research should implement
follow-up measures to assess the time course changes of
performance to appropriately diagnose FOR, NFOR or OTS.
The lack of longitudinal interventions which have dem-
onstrated training maladaptation presents difficulties in the
attempt to monitor and diagnose overtraining. It appears as
though maximal muscular strength is resilient to large acute
increases in training load. Therefore, secondary performance
measures may be useful for the early detection of FOR,
Overtraining in Resistance Exercise…
NFOR or OTS in resistance-trained athletes. Previous stud-
ies have employed a variety of performance measures (e.g.
sprint time, vertical jump height) not specific to the resist-
ance training protocol that may provide important insight
into the monitoring of possible overtraining [14–16, 21].
Contrasting results were reported for secondary performance
measures. Collectively, it appears as though changes in max-
imal strength may not reflect performance in other tasks.
Future studies should aim to appropriately establish FOR,
NFOR or OTS and determine whether such tests could be
used to monitor the manifestation of these conditions. Per-
formance testing is an efficient and inexpensive method to
monitor and prevent overtraining. However, given the short
duration and wide variety of performance measures used by
many studies, there remains insufficient evidence to reach
a consensus on performance tests that monitor overtraining
in resistance exercise.
The majority of the literature on overtraining in resistance
exercise has been reported following interventions where
physical performance was not adversely affected. Although it
is difficult to compare without consistent measures between
studies, differences in the prescription of overload training
protocols may provide insight into the type of resistance
training that may increase susceptibility to overtraining. The
training frequency and relative training intensity of interven-
tions that did induce performance decrements appear to be
higher than those that did not adversely affect performance.
All studies that performed multiple sets of one repetition at
high intensity (e.g. 10 sets × 1 repetition at 100% 1RM, every
day for 2weeks) were able to induce performance decreases
[11–13, 16]. Low volume, high-intensity and -frequency
protocols such as those used in these interventions may be
insightful for research purposes. However, coaches and ath-
letes are unlikely to implement such regimes as part of a
training program due to the risk of injury associated with
training at maximal loads [33]. Previous studies that dem-
onstrated no adverse effects on performance implemented
training protocols that are likely more reflective of how
resistance-based athletes would normally train. However,
as many overtraining studies have been unable to induce
FOR, NFOR or OTS and the concomitant performance
decrements, the trade-off between ecological validity and
adequate manipulation of exercise volume and/or intensity
to elicit a maladaptive response must be considered. These
studies may still provide important insight into resistance
exercise FOR, NFOR and OTS.
Training monotony may be expressed as the amount of
variation in training load within one training cycle [34].
A previous study has suggested that monotonous training
increases susceptibility to overreaching and overtraining in
endurance activities [35]. Although there is little empiri-
cal evidence examining the relationship between training
monotony and overtraining, it appears as through monotony
of training load may increase the likelihood of overtraining
in resistance exercise. Many previous studies that reported
performance decrements utilised interventions where only
one type of resistance exercise was performed (i.e. squat)
[11–14, 16, 19, 20]. It appears as though low variation in
exercise selection or targeted muscle groups may increase
the likelihood of training maladaptation due to a high
increase in concentrated training load with limited time to
recover. Therefore, coaches and athletes should use caution
when programming an overload period targeting a specific
lift or muscle group. Collectively, high training frequency,
high training intensity and training monotony appear to
increase the likelihood of training maladaptation. However,
confounding factors such as training status must be consid-
ered in future studies.
4.1.3 Biochemistry
Various biochemical markers have also been investigated to
gain a greater understanding of the potential mechanisms of
overtraining in resistance exercise. Nine studies measured
biochemical responses following an overload training period
that resulted in a decrease in performance [11–13, 15–18,
20, 21]. Marked responses were observed in overload par-
ticipants in comparison to control participants in hormone
levels (cortisol, T:C ratio, free T:C ratio and catecholamines)
[11, 12, 20], blood biomarkers and muscle damage markers
(lactate and creatine kinase, respectively) [13]. However,
the biochemical responses of overtraining remain unknown
due to the variability of results and lack of studies that have
measured the time course changes in performance required
to accurately diagnose maladaptive training conditions. A
recent systematic review of the hormonal aspects of over-
training by Cadegiani etal. [36] also recognised that the
improper diagnosis of FOR, NFOR and OTS is a significant
problem in overtraining literature. Furthermore, biochemical
markers have been unable to distinguish between a normal
training response, acute fatigue, FOR, NFOR and OTS. Fur-
ther research is needed to understand the biochemical altera-
tions during training maladaptation and to determine the
validity and reliability of biomarkers for monitoring over-
training. It has previously been suggested that overtraining
can result in differential biochemical responses depending
on whether high relative intensity or high-volume resist-
ance training is performed [8, 37]. However, due to the lack
of studies that have appropriately established overtraining
through high-volume and/or high-intensity training proto-
cols, comparisons cannot be made; therefore, this theory
cannot be corroborated.
C.Grandou et al.
4.1.4 Physiology
Physiological measures have previously been investigated
as tools to monitor and/or diagnose overtraining. However,
relatively few studies have investigated the response of
physiological measures to overtraining in resistance exer-
cise. Fry etal. [13] measured resting heart rate upon waking
and reported no changes throughout 2weeks of overload
resistance training. However, the multifactorial causes of
variation in basal heart rate may limit its ability to moni-
tor for overtraining in resistance exercise. Additionally,
Margonis etal. [18] reported on knee range of motion as
a measure of the swelling/oedema response to overtraining
in resistance exercise. The authors reported a decrease in
range of motion indicative of swelling and muscle micro
trauma following the overload training intervention. How-
ever, inflammatory measures may be unable to distinguish
between acute fatigue, FOR, NFOR and OTS. The muscle
physiology mechanisms that underpin the decline in perfor-
mance characteristic of overtraining in resistance exercise
have been investigated by relatively few studies [16, 19, 20].
Skeletal muscle fibre composition and muscle fibre contrac-
tile properties have previously been examined. Declines in
β2-AR density and altered MAPK activity may be responsi-
ble for the muscle maladaptation associated with overtrain-
ing. However, future research is needed to determine the
validity and reliability of physiological measures as tools
to monitor overtraining in resistance exercise. Furthermore,
physiological monitoring markers must reflect the nature and
mechanisms of resistance training.
4.1.5 Psychology andPerceptual Responses
It is well established that the presence of negative psycho-
logical and perceptual responses coincides with overtraining
in endurance populations [7]. However, relatively few stud-
ies have used psychological and perceptual monitoring tools
in resistance exercise overtraining interventions. Increases in
delayed onset muscle soreness and pain as well as decreases
in perceived recovery status and perception of strength have
been reported among interventions that demonstrated a
decrease in performance [13, 18]. These are expected find-
ings given that the process of overtraining involves an imbal-
ance of training stress and recovery. In contrast to the endur-
ance literature, Fry etal. [13] reported slight decreases in
anxiety following an overload training period which resulted
in decreases in 1RM strength. The authors suggested that
overtraining through high-intensity resistance exercise may
produce different psychological responses in comparison
to high-volume endurance training. At present, percep-
tual measures of soreness and recovery status may provide
information concerning increases in training load. However,
these tools are yet to be established as reliable indicators of
overtraining in resistance exercise. Due to the lack of studies
demonstrating overtraining and investigating psychological
and perceptual responses to overtraining in resistance exer-
cise, no clear consensus can be reached. Future investigators
should combine tools to measure psychological disturbances
with measures of performance to gain a better understanding
of this relationship.
4.2 Limitations
This is the first systematic review to critically appraise the
methodology and results of studies that have attempted to
induce FOR, NFOR or OTS through resistance exercise.
This analysis was limited by the inability to perform a meta-
analysis due to the heterogeneity of study methodologies and
outcomes. Additionally, a possible risk of bias may exist
in the selection of search terms and exclusion criteria as
defined by the authors. However, this review followed pro-
tocols as recommended by the AMSTAR 2 and PRISMA
guidelines. Furthermore, due to the criteria required to
diagnose overtraining, an adapted risk of bias assessment
tool was required to accurately reflect the quality of studies.
Limitations are present in this assessment as a clear judge-
ment about the risk of bias arising from each domain was not
reflected with a validated assessment tool (i.e. Cochrane risk
of bias appraisal tool). To address this limitation, an adapted
risk of bias assessment tool was used. Additionally, a variety
of limitations exist in the included studies. Many studies
did not demonstrate decreases in performance or measure
the time course changes in performance during a follow-up
period. Due to these methodological limitations, an accurate
diagnosis of FOR, NFOR or OTS was impossible. The lack
of standardised diagnostic criteria and the inconsistency and
variability in measurements of performance, biochemistry,
physiology and psychology amongst studies make it difficult
to establish the relationship between overtraining and resist-
ance exercise.
4.3 Future Research
Given the negative impact of overtraining on athletic perfor-
mance, it is essential that research in this area is examined
critically. Due to the lack of studies demonstrating decreases
in performance and implementing follow-up measures,
further research is required to develop an understanding
of overtraining in resistance exercise. The prevalence and
symptoms of overtraining in resistance exercise should be
further investigated given the lack of longitudinal studies in
resistance-trained populations. Future studies must imple-
ment resistance training interventions that are reflective of
the sport/discipline to maintain ecological validity; however,
the authors should report the primary performance measure.
To gain a better understanding of the effects of overtraining,
Overtraining in Resistance Exercise…
future studies should attempt to increase consistency
amongst measured parameters (biochemical, physiological
and psychological markers). There is also a need to inves-
tigate the time course changes in performance, biochem-
istry, physiology and psychology throughout the recovery/
follow-up stage. Future investigators should also consider
examining the aetiology of high-volume versus high rela-
tive intensity resistance exercise overtraining. Additionally,
future authors should control for confounding factors (i.e.
nutritional and sleep characteristics) as these factors may
play a role in the development of the OTS [38]. As was
recently done in an overtraining study by Cadegiani etal.
[38], future authors should consider utilising the flowchart
proposed by Meeusen etal. [7] to diagnose OTS and account
for confounding factors.
It is necessary to consider the clinical and economic
implications of studying overtraining in athletic populations.
Future researchers must consider the impact of subjecting
participants to increased training loads over long periods in
an attempt to induce overtraining. This may result in long-
term decrements in performance and increased susceptibility
to physical or psychological illness and injury. Additionally,
overtraining may be experienced differently amongst partici-
pants. Future studies must consider interindividual variabil-
ity in response to increases in training load. While the dif-
ficulties and ethical considerations of inducing overtraining
in athletic populations are appreciated, well-designed studies
with demonstrated decreases in performance and follow-up
measures are required to develop a greater understanding of
overtraining in resistance exercise.
5 Conclusion
The primary aim of this review was to critically analyse the
existing literature to elucidate the mechanisms that underlie
overtraining in resistance exercise. Despite the potentially
serious implications of overtraining in athletic populations,
to date, there is insufficient literature investigating the effects
of FOR, NFOR and OTS in resistance exercise. The majority
of previous resistance-based overtraining interventions fail
to demonstrate decrements in training-specific performance.
Furthermore, many studies do not accurately measure the
length of recovery and time course changes in physical per-
formance. It is apparent that the misdiagnosis of overtraining
is a significant problem in previous research. However, it is
necessary to mention that whilst many studies did not appro-
priately establish FOR, NFOR or OTS they still provide
valuable information regarding the physiological alterations
and potential mechanisms of resistance training fatigue.
At present, there is insufficient evidence to draw accu-
rate conclusions on the effects of overtraining in resist-
ance exercise. No diagnostic tool other than a decrease in
sport-specific performance can be taken as an indicator of
overtraining in resistance exercise. Given the current evi-
dence the exact role of biochemical, physiological and psy-
chological markers in overtraining in resistance exercise
remains equivocal. Athletes and coaches should regularly
monitor a combination of performance, biochemical, physi-
ological and psychological variables to identify athletes that
may be approaching training maladaptation. The causes and
pathogenic nature of overtraining remain unclear; however,
frequent, high-intensity, monotonous resistance training
appears to increase an athlete’s susceptibility to overtrain-
ing. However, caution must be exercised when interpreting
these findings due to the lack of interventions which have
induced FOR, NFOR or OTS through resistance exercise.
Data availability statement All data generated or analysed during
this study are included in this published article (and its supplementary
information files).
Compliance with ethical standards
Funding No sources of funding were used to assist in the preparation
of this article.
Conflict of interest Clementine Grandou, Lee Wallace, Franco M.
Impellizzeri, Nicholas G. Allen and Aaron J. Coutts declare that they
have no conflicts of interest relevant to the content of this review.
References
1. Kraemer WJ, Adams K, Cafarelli E, et al. American col-
lege of sports medicine position stand. Progression models in
resistance training for healthy adults. Med Sci Sports Exerc.
2002;34(2):364–80.
2. Kraemer WJ, Ratamess NA. Fundamentals of resistance train-
ing: progression and exercise prescription. Med Sci Sports Exerc.
2004;36(4):674–88.
3. Kuipers H, Keizer HA. Overtraining in elite athletes. Sports Med.
1988;6(2):79–92.
4. Urhausen A, Kindermann W. Diagnosis of overtraining: what
tools do we have? Sports Med. 2002;32(2):95–102.
5. Fry RW, Morton AR, Keast D. Periodisation and the prevention
of overtraining. Can J Sport Sci. 1992;17(3):241–8.
6. Halson SL, Bridge MW, Meeusen R, etal. Time course of perfor-
mance changes and fatigue markers during intensified training in
trained cyclists. J Appl Physiol. 2002;93(3):947–56.
7. Meeusen R, Duclos M, Foster C, etal. Prevention, diagnosis, and
treatment of the overtraining syndrome: joint consensus statement
of the European college of sport science and the American college
of sports medicine. Med Sci Sports Exerc. 2013;45(1):186–205.
8. Fry AC, Kraemer WJ. Resistance exercise overtraining
and overreaching: neuroendocrine responses. Sports Med.
1997;23(2):106–29.
9. Fry AC, Webber JM, Weiss LW, etal. Impaired performances
with excessive high-intensity free-weight training. J Strength
Cond Res. 2000;14(1):54–61.
10. Moher D, Liberati A, Tetzlaff J, etal. Preferred reporting items
for systematic reviews and meta-analyses: the PRISMA statement.
PLos Med. 2009;6(7):e1000097.
C.Grandou et al.
11. Fry AC, Kraemer WJ, Ramsey LT. Pituitary-adrenal-gonadal
responses to high-intensity resistance exercise overtraining. J Appl
Physiol. 1998;85(6):2352–9.
12. Fry AC, Kraemer WJ, Van Borselen F, etal. Catecholamine
responses to short-term high-intensity resistance exercise over-
training. J Appl Physiol. 1994;77(2):941–6.
13. Fry AC, Kraemer WJ, Van Borselen F, etal. Performance decre-
ments with high-intensity resistance exercise overtraining. Med
Sci Sports Exerc. 1994;26(9):1165–73.
14. Fry AC, Kraemer WJ, Lynch JM, etal. Does short-term near-
maximal intensity machine resistance training induce overtrain-
ing? J Strength Cond Res. 1994;8(3):188–91.
15. Fry AC, Kraemer WJ, Stone MH, etal. Endocrine and perfor-
mance responses to high volume training and amino acid sup-
plementation in elite junior weightlifters. Int J Sport Nutr.
1993;3(3):306–22.
16. Fry AC, Schilling BK, Weiss LW, etal. Beta2-adrenergic
receptor downregulation and performance decrements during
high-intensity resistance exercise overtraining. J Appl Physiol.
2006;101(6):1664–72.
17. Hecksteden A, Skorski S, Schwindling S, etal. Blood-borne mark-
ers of fatigue in competitive athletes—results from simulated
training camps. PLoS One. 2016;11(2):e0148810.
18. Margonis K, Fatouros IG, Jamurtas AZ, etal. Oxidative stress
biomarkers responses to physical overtraining: implications for
diagnosis. Free Radic Biol Med. 2007;43(6):901–10.
19. Nicoll JX, Fry AC, Galpin AJ, et al. Changes in resting
mitogen-activated protein kinases following resistance exer-
cise overreaching and overtraining. Eur J Appl Physiol.
2016;116(11–12):2401–13.
20. Sterczala A, Fry A, Chiu L, etal. β2-adrenergic receptor malad-
aptations to high power resistance exercise overreaching. Hum
Physiol. 2017;43(4):446–54.
21. Warren BJ, Stone MH, Kearney JT, etal. Performance measures,
blood lactate, and plasma ammonia as indicators of overwork in
elite junior weightlifters. Int J Sports Med. 1992;13(5):372–6.
22. Fahey TD, Pearl MS. The hormonal and perceptive effects of
phosphatidylserine administration during 2weeks of resistive
exercise-induced overtraining. Biol Sport. 1998;15(3):135–44.
23. Fatouros IG, Destouni A, Margonis K, etal. Cell-free plasma
DNA as a novel marker of aseptic inflammation severity related
to exercise overtraining. Clin Chem. 2006;52(9):1820–4.
24. Fry AC, Kraemer WJ, Stone MH, etal. Endocrine responses to
overreaching before and after 1year of weightlifting. Can J Sport
Sci. 1994;19(4):400–10.
25. Hasegawa Y, Kurosawa Y, Goto K. The effect of planned over-
reaching and short-term detraining on jump squat performance. J
Aust Strength Cond. 2016;24(7):13–8.
26. Kraemer WJ, Ratamess NA, Volek JS, etal. The effects of amino
acid supplementation on hormonal responses to resistance training
overreaching. Metabolism. 2006;55(3):282–91.
27. Lowery RP, Joy JM, Rathmacher JA, etal. Interaction of beta-
hydroxy-beta-methylbutyrate free acid and adenosine triphosphate
on muscle mass, strength, and power in resistance trained indi-
viduals. J Strength Cond Res. 2016;30(7):1843–54.
28. Raastad T, Glomsheller T, Bjoro T, etal. Changes in human skel-
etal muscle contractility and hormone status during 2weeks of
heavy strength training. Eur J Appl Physiol. 2001;84(1–2):54–63.
29. Ratamess NA, Kraemer WJ, Volek JS, etal. The effects of amino
acid supplementation on muscular performance during resistance
training overreaching. J Strength Cond Res. 2003;17(2):250–8.
30. Sweeny M, Brilla L, Suprak D, etal. Comparison of linear and
daily undulating periodization in resistance training using simple
measures of overreaching. Med Sci Sports Exerc. 2011;43(Suppl
1):836.
31. Wilson J, Lowery R, Joy J, etal. The effects of 12weeks of beta-
hydroxy-beta-methylbutyrate free acid supplementation on mus-
cle mass, strength, and power in resistance-trained individuals: a
randomized, double-blind, placebo-controlled study. Eur J Appl
Physiol. 2014;114(6):1217–27.
32. Gentles JA, Phillips SM. Discrepancies in publications related to
HMB-FA and ATP supplementation. Nutr Metab. 2017;14(1):42.
33. Keogh J, Hume PA, Pearson SJJOS. Retrospective injury epide-
miology of one hundred one competitive Oceania power lifters:
the effects of age, body mass, competitive standard, and gender. J
Strength Cond Res. 2006;20(3):672–81.
34. McGuigan MR, Foster C. A new approach to monitoring resist-
ance training. J Strength Cond Res. 2004;26(6):42.
35. Bruin G, Kuipers H, Keizer H, etal. Adaptation and overtraining
in horses subjected to increasing training loads. J Appl Physiol.
1994;76(5):1908–13.
36. Cadegiani FA, Kater CE. Hormonal aspects of overtraining
syndrome: a systematic review. BMC Sports Sci Med Rehabil.
2017;9(1):14.
37. Kreider RB, Fry AC, O’Toole ML. Overtraining in sport. Cham-
paign: Human Kinetics; 1998.
A preview of this full-text is provided by Springer Nature.
Content available from Sports Medicine
This content is subject to copyright. Terms and conditions apply.
