REVIEW Recovery from Exercise
Recovery of central and peripheral neuromuscular fatigue after exercise
X T. J. Carroll,
1
J. L. Taylor,
2
and S. C. Gandevia
2
1
Centre for Sensorimotor Performance, School of Human Movement and Nutrition Sciences, University of Queensland;
and
2
Neuroscience Research Australia and University of New South Wales
Submitted 2 September 2016; accepted in final form 2 December 2016
Carroll TJ, Taylor JL, Gandevia SC. Recovery of central and peripheral
neuromuscular fatigue after exercise. J Appl Physiol 122: 1068 –1076, 2017. First
published December 8, 2016; doi:10.1152/japplphysiol.00775.2016.—Sustained
physical exercise leads to a reduced capacity to produce voluntary force that
typically outlasts the exercise bout. This “fatigue” can be due both to impaired
muscle function, termed “peripheral fatigue,” and a reduction in the capacity of the
central nervous system to activate muscles, termed “central fatigue.” In this review
we consider the factors that determine the recovery of voluntary force generating
capacity after various types of exercise. After brief, high-intensity exercise there is
typically a rapid restitution of force that is due to recovery of central fatigue
(typically within 2 min) and aspects of peripheral fatigue associated with excita-
tion-contraction coupling and reperfusion of muscles (typically within 3–5 min).
Complete recovery of muscle function may be incomplete for some hours, how-
ever, due to prolonged impairment in intracellular Ca
2⫹
release or sensitivity. After
low-intensity exercise of long duration, voluntary force typically shows rapid,
partial, recovery within the first few minutes, due largely to recovery of the central,
neural component. However, the ability to voluntarily activate muscles may not
recover completely within 30 min after exercise. Recovery of peripheral fatigue
contributes comparatively little to the fast initial force restitution and is typically
incomplete for at least 20 –30 min. Work remains to identify what factors underlie
the prolonged central fatigue that usually accompanies long-duration single joint
and locomotor exercise and to document how the time course of neuromuscular
recovery is affected by exercise intensity and duration in locomotor exercise. Such
information could be useful to enhance rehabilitation and sports performance.
central fatigue; endurance, exercise; muscle fatigue; recovery
SUSTAINED PHYSICAL EXERCISE leads inexorably to a reduced
capacity to produce voluntary force. Although multiple pro-
cesses contribute to this “muscle fatigue,” it is ultimately
manifest as impaired muscle function and/or a reduction in the
capacity of the central nervous system to activate muscles. The
term “peripheral fatigue” is typically used to describe force
reductions due to processes distal to the neuromuscular junc-
tion, whereas those due to processes within motoneurons and
the central nervous system are commonly known as “central
fatigue.” The physiology of fatigue has been studied for well
over a century (see Ref. 28 for a comprehensive historical
review), and recent reviews have summarized current under-
standing of various aspects of fatigue (2, 13, 23, 62, 84, 92,
93). As part of this Highlighted Topic series, we consider the
factors that determine the recovery of voluntary force-gener-
ating capacity after various types of exercise.
In attempting to document the mechanisms of fatigue and
recovery, an important consideration is that sustained exercise
affects physiological processes throughout the neuromuscular
system. Critically, alterations in these underlying processes
may either contribute to, or compensate for, fatigue (see
sections below for examples and details). Although some
progress has been made in documenting interrelationships
between exercise characteristics, physiological responses, and
impaired force-generating capacity, much remains to be
learned. Given this, and the constraints of the review format,
we consider primarily recovery of neuromuscular performance
in terms of voluntary or artificially evoked forces measured in
intact humans. We attempt to link these functional measures of
fatigue with the likely underlying processes where possible and
highlight areas in which a lack of available evidence prevents
this. As a consequence of our focus on work that we believe
provides the clearest inferences regarding the mechanisms of
recovery, a number of interesting and important issues are
omitted. For example, we do not consider the effects of
low-intensity exercise, nutrition, or other interventions on the
recovery process. Some of these issues are dealt with in other
papers in the Highlighted Topic series.
Because of the task-dependent nature of fatigue (23), the
review is structured according to sections that each consider
Address for correspondence: T. Carroll, School of Human Movement and
Nutrition Sciences, The University of Queensland, St Lucia, Qld, 4072,
Australia (e-mail: timothy.carroll@uq.edu.au).
J Appl Physiol 122: 1068–1076, 2017.
First published December 8, 2016; doi:10.1152/japplphysiol.00775.2016.
8750-7587/17 Copyright
©
2017 the American Physiological Society http://www.jappl.org1068
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the classes of exercise in which recovery has been documented.
We initially consider maximal voluntary contractions at a
single joint, because central fatigue is most easily studied in
this type of task. In particular, we extrapolate recent insights
into the mechanisms of central fatigue in these tasks to the
postexercise recovery period. We then consider what general
implications can be drawn about recovery from apparent dif-
ferences in fatigue and recovery between maximal and sus-
tained submaximal contractions at a single joint. Finally, we
consider recovery from everyday exercise, such as running and
cycling, which involve large muscle masses, and consequently
challenge systemic homeostasis.
Recovery from Maximal Contractions
A reduction in the maximal force that a person can produce
during a isometric maximal voluntary contraction (MVC) pro-
vides the most straightforward demonstration of fatigue. Ac-
cordingly, tasks involving a sustained MVC provide a conve-
nient model to study fatigue and recovery, because there is a
continuous measure of fatigue during the protocol (i.e., instan-
taneous MVC force) and because recovery can easily be
tracked with the same apparatus used to induce fatigue (i.e.,
without the requirement to reposition the subject or switch
between tasks). Isometric conditions are also convenient for
measurement of forces evoked artificially by electrical or
magnetic stimulation of motor nerves, descending tracts, or the
motor cortex. Evoked forces at rest can provide information
about fatigue and recovery of the muscle fibers, whereas force
responses to stimulation that is “superimposed” upon voluntary
contractions can reveal the extent to which voluntary neural
drive is sufficient to generate the maximal force of which the
muscles are capable.
It is important to acknowledge that, although measures
obtained during MVC provide valid and easily interpreted
information about neuromuscular function, such measures may
not be ideally sensitive to some physiological changes that are
important for exercise performance. Examples that demon-
strate this point include observations of exacerbated force
declines during low-frequency motor unit firing (16, 22, 83, 95,
102) and observations that some interventions such as hyper-
thermia (98) or prior locomotor exercise (83) have much
greater effects on sustained than brief MVC performance.
Despite these limitations, in many cases measurements ob-
tained during MVC provide the best available evidence regard-
ing muscle force-generating capacity and the capacity of the
central nervous system to drive muscles, and the current review
will focus extensively on work that exploits these measures.
Maximal voluntary force declines rapidly and progressively
during a sustained MVC, typically falling to below 50% of
baseline within 1–2 min. There is also a rapid but partial
recovery of voluntary force over the first few minutes after
cessation of this type of exercise, with the largest component
occurring within 15–30 s. This suggests that reperfusion of the
exercising muscles is a key factor in initial recovery, a con-
clusion supported by the observation that recovery is delayed if
the muscles are held ischemic. Further recovery of MVC force
is much slower and may reach only ~80% by 4 –5 min
postexercise (see Fig. 1A and Refs. 29, 50, 98).
The size of superimposed twitches evoked by stimulation of
motor nerves or the motor cortex also increases within 15–30 s
of sustained MVC, indicating that part of the voluntary force
reduction is due to suboptimal output from the motor cortex
(29, 40, 41, 48, 50, 51, 91, 98). This failure of voluntary
activation has been estimated to account for ~25% (100) of the
total force reduction during sustained maximal contractions,
but voluntary activation usually completely recovers to prefa-
tigue levels within ~30 s of exercise termination (see Fig. 1C
and Refs. 29, 48, 50, 51, 98). The dissociation in the time
course of recovery between MVC and voluntary activation
implies that the sustained impairments in voluntary force
production originate predominantly within the muscle fibers.
Further support for this conclusion derives from observations
of prolonged, incomplete recovery of electrically evoked
twitches and tetani after repeated isometric contractions to the
limit of tolerance (22).
Mechanisms of Recovery
A detailed coverage of what is currently known about the
physiological processes that accompany sustained exercise is
beyond the scope of this paper, but see Taylor et al. (92) and
Allen et al. (2) for fuller accounts of central and peripheral
fatigue mechanisms, respectively. Here, we provide a brief
overview (see Fig. 2 for a summary) and emphasize that the
time courses of change in these processes need not reflect that
of the functional recovery in voluntary force. This is because
physiological responses to sustained exercise may either con-
tribute to, or compensate for fatigue, and recovery of voluntary
force is ultimately determined by the interplay of such under-
lying processes. For example, during sustained maximal con-
tractions, both the excitatory and the inhibitory (silent period)
responses of motor cortex output cells to transcranial magnetic
stimulation increase. These changes suggest extra cortical
excitability, which should improve motor output, but also extra
cortical inhibition, which might contribute to fatigue. At the
same time the extent to which voluntary output from the cortex
can harness the full capacity of muscles decreases (i.e., there is
supraspinal fatigue; e.g., Refs. 29, 40, 41, 91). Stimulation
during intermittent MVCs with different duty cycles shows that
these three effects have different time courses of development
and return to baseline, with the silent period returning to
baseline in ~10 s, the excitatory response to cortical stimula-
tion in 15–30 s, and supraspinal fatigue in ~1 min (91).
Although the factors that underlie a failure to harness the full
capacity of cortical outputs to drive motoneurons appropriately
for maximal voluntary force generation are not known, a role
for feedback from group III and IV muscle afferents is likely.
When firing of metabolically sensitive muscle afferents is
prolonged after a fatiguing contraction by preventing blood
flow to the muscle, supraspinal fatigue continues until blood
flow is allowed to resume (29, 51). Moreover, firing of affer-
ents from the fatigued muscle affects voluntary activation of
other muscles in the same limb (50, 51). In contrast, the
excitatory and inhibitory responses elicited by stimulation of
the motor cortex typically return to pre-exercise values despite
the occlusion (29, 51). This suggests that muscle afferent firing
may limit drives to the motor cortex (and other descending)
output cells during maximal effort, without apparent direct
actions on motor cortical cells. However, debate continues on
the actions of group III and IV afferents on motor cortical
excitability because responses evoked by stimulation of the
1069Recovery of Central and Peripheral Fatigue • Carroll TJ et al.
J Appl Physiol • doi:10.1152/japplphysiol.00775.2016 • www.jappl.org
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cortex and measured in the muscle are influenced by both
cortical and spinal excitability. Hence interpretation of changes
in responses to cortical stimulation is not clear cut (49). Indeed,
it is possible that supraspinal fatigue could occur despite
relatively stable outputs from supraspinal centers. Here, central
fatigue would be generated by changes in input-output prop-
erties of the motoneuron pool, such that a similar set of cortical
outputs that are untapped by volition and available to artificial
stimulation would have a proportionally greater effect on
muscle force.
In contrast to the uncertainty regarding supraspinal contri-
butions to fatigue, it is clear that central fatigue must be
affected by the motoneuron pool itself (see Refs. 28, 57, 92 for
reviews). Changes at this level can arise from tonic and phasic
reflex inputs and other inputs associated with the exercise as
well as changes in intrinsic properties of the motoneurons.
Superimposed on such changes are neuromodulatory effects,
produced for example, by descending monoaminergic drives.
Although these changes are the focus of current work in human
and animal studies, it is not simple to link their effect to a
precise aspect of motoneuronal or spinal behavior or to deter-
mine their effect on motor output in a voluntary contraction.
However, two things are clear. First, changes in the excitability
of the motoneuron pool must be compensated by changes in
descending drive to keep motoneuronal output constant. Hence
a reduction in excitability (through inhibition or disfacilitation,
see below) would necessitate greater drive. Such a reduction
would likely produce a greater subjective effort for the same
submaximal motor output. Second, the changes documented so
far at a motoneuronal level have a range of time courses,
ranging from milliseconds to minutes. Some examples are
given briefly below.
Inputs from group III/IV muscle afferents can act at seg-
mental sites to modify excitability of the motoneurons and at
supraspinal sites to affect the level of drive to the motoneuron
pools (13, 18, 28, 57, 85). Existence of these effects has long
been studied with circulatory occlusion (e.g., Ref. 14). Not
surprisingly, restoration of muscle blood flow and removal of
K
⫹
and other metabolites rapidly attenuates the central effects
of group III/IV muscle afferent firing with recovery of volun-
tary activation in ~30 s (48, 50, 51). More recently, lumbar
intrathecal injection of fentanyl has been used to reduce group
III/IV inputs to the central nervous system and attenuate an
inhibition of voluntary motor output (e.g., Refs. 3, 5).
Two approaches illustrate depression of motoneuronal “ex-
citability” after voluntary isometric exercise. First, during re-
laxation after contraction, the propensity of the motoneurons to
discharge a recurrent action potential (termed an F wave) is
Δ MVC (%)
Post exercise time (min)
Δ twitch force (%)
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
-80
-70
-60
-50
-40
-30
-20
-10
0
-40
-35
-30
-25
-20
-15
-10
-5
0
-40
-35
-30
-25
-20
-15
-10
-5
0
5
0.5 5 50 500 5000
Δ voluntary activation (%)
-80
-70
-60
-50
-40
-30
-20
-10
0
Post exercise time (min)
0.5 5 50 500 5000
Post exercise time (min)
0.5 5 50 500 5000
-80
-70
-60
-50
-40
-30
-20
-10
0
0 10203040-10
Post exercise time (min)
0 10203040-10
Post exercise time (min)
010203040-10
Post exercise time (min)
2-3 mins
2-3 mins hand
>20 mins
<12 mins
>5 hours
40-90 mins
Δ MVC (%)
Δ twitch force (%)
Δ voluntary activation (%)
ABC
DEF
Fig. 1. Percentage change in MVC (A, D), twitch amplitude (B, E), and voluntary activation (C, F) measured at various times after the cessation of fatiguing
exercise. A–C show data from isometric contractions; D–F show data from locomotor exercise. Values are taken from text or estimated from figures across a
number of papers. Some papers contribute multiple points and others only one. No distinction was made between voluntary activation measured with motor nerve
or motor cortex stimulation. Note that the time postexercise in minutes is on a logarithmic scale for the locomotor exercise only. Papers contributing to the graphs
for isometric contractions of 2–3 min (open circles) are (29, 32, 48, 51, 98). For 2–3 min contractions of hand muscles (green triangles), contributors are (50,
76). For contractions of ⬎20 min (solid circles), contributing papers are (88, 89, 102, 106). Apart from the hand muscles, data are from elbow flexors and knee
extensors. Papers contributing to the locomotor exercise graphs for exercise of ⬍12 min (open circles) are (33, 35, 86, 96, 97). Contributing papers for exercise
of 40 –90 min (gray triangles) are (16, 74, 75, 83). For exercise of ⬎5 h (solid circles), papers are (58, 65, 72, 94, 95). Exercise of ⬍12 min represents only knee
extensors, whereas both longer durations also contain some plantarflexor data. Also of note, the exercise of ⬎5 h was running, 40 –90 min included cycling,
running, and a soccer game, and exercise of ⬍12 min included cycling and one study of running.
1070 Recovery of Central and Peripheral Fatigue • Carroll TJ et al.
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depressed for several minutes after a 2-min MVC (e.g., Refs.
52, 81). This depression occurs in hand and leg muscles and is
less for weaker contractions (53). Although in simple terms
this can be considered a depression in intrinsic motoneuronal
behavior (i.e., because it is seen in an evoked response that
does not require synaptic activation), one constraint is that the
measurement is dominated by changes in large high-threshold
motoneurons in the pool (e.g., Refs. 24).
Second, evidence for profound change at a spinal level
comes from the use of high-intensity conditioning TMS during
an MVC to interrupt descending voluntary drive and allow the
motoneurons to be tested during artificial “relaxation.” Testing
is done with a cervicomedullary stimulus, which produces a
muscle response by activation of corticospinal axons. Studying
motoneuron behavior in the absence of volitional activity
greatly simplifies the range of factors that are at play and
makes it possible to determine mechanisms. After 15 s of an
MVC of elbow flexors, the corticospinal response is virtually
abolished (61). This spinal inhibition affecting the corticomo-
toneuronal path takes 2–3 min to recover after the end of the
fatiguing MVC. The phenomenon also occurs during and after
submaximal contractions and preferentially affects the mo-
toneurons active in the contraction (59).
Finally, although detailed consideration of the intramuscular
processes that determine recovery from exercise are beyond
our scope (refer to Ref. 2), characteristics of evoked forces
illustrate some general principles. For example, reductions in
evoked twitch magnitude and tetanic forces evoked by low-
frequency stimulation are consistently greater than declines in
MVC or high-frequency tetanic force (16, 22, 83, 95, 102). The
time course of recovery of forces evoked by high-frequency
stimulation is also much more rapid than that of recovery of
low-frequency stimulation forces (or twitches). Force produced
by high-frequency stimulation returns near to baseline within
20 min, even after a prolonged series of contractions to the
limit of endurance in the presence of ischemia, whereas low-
frequency force impairments can persist for more than 24 h
(22). Differential fatigue and recovery effects as a function of
motoneuron firing frequency likely follow from the sigmoidal
shape of the Ca
2⫹
force relation (2) and may reflect alterations
in release or reuptake of Ca
2⫹
from the sarcoplasmic reticulum
or reduced Ca
2⫹
sensitivity at the contractile apparatus. Note
that single twitches create conditions that lie close to the origin
of the Ca
2⫹
force relation. By contrast, the rapid partial
restitution of high-frequency force in the first seconds of
recovery probably follows from muscle reperfusion, with
clearance of K
⫹
allowing repolarization of the t-tubule mem
-
branes likely to play a major role (2).
Moreover, the general principle that responses to sustained
exercise can either contribute to, or compensate for, fatigue
holds for peripheral as well as central processes. For example,
exercise can cause a slowing in the contractile properties of
muscle, such that a lower rate of muscle fiber action potentials
is required to generate a fully fused tetanus (39, 100, 103). This
type of effect would partially compensate centrally mediated
declines in motoneuronal firing rates, although the presence of
central fatigue underscores the fact that, despite this partial
compensation, voluntary drive is insufficient to generate the
maximum evocable muscle force.
Recovery from Sustained Submaximal Contractions
The contrast between the fatigue responses in maximal and
sustained or intermittent submaximal contractions can inform
understanding of the factors that determine recovery after
exercise (93). Although central fatigue cannot be measured
using peripheral or cortical stimulation during the submaximal
task, it can be documented during maximal efforts inserted
within the main task. Furthermore, although not a direct mea-
sure of central fatigue, perceived effort increases out of pro-
portion to the level of EMG. This is best seen in a sustained
contraction in which the participant holds a submaximal target
EMG level. In such contractions, the alteration in the EMG to
force relationship produced by peripheral fatigue results in
reduced force output. However, participants report that pro-
gressively more effort is required to do the task; which is to
produce the same EMG (e.g., Ref. 60). This suggests that
central mechanisms also influence performance during sub-
maximal tasks (56, 80, 81). A key distinction between maximal
and submaximal tasks is that additional motor units are pro-
gressively recruited as fatigue develops during sustained low-
force contractions (1, 19, 30). By contrast, it is likely that all
available motor units are recruited at high rates at the begin-
ning of a sustained MVC and firing rates progressively decline
with fatigue and may eventually cease in some high-threshold
units (e.g., Ref. 71). Thus, for a given contraction duration, less
fatigue occurs in high-threshold units for submaximal than
Excitation-contraction
coupling failure (mins-hrs)
- e.g. K
+
in T-tubules
- reduced SR Ca
2+
release
Cross-bridge effects
(secs-mins)
- reduced Ca
2+
sensitivity
- reduced maximum force
of contractile apparatus
Firing of group III / IV
musle afferents
(secs-mins)
- exaggerated with poor
muscle perfusion
Presynaptic inhibition
- time course ?
Reduced synaptic efficacy
- time course ?
Reduced intrinsic MN
responsiveness (mins)
- in MNs that fire repeatedly
Suboptimal cortical
and other drives (secs-hrs?)
- mechanisms?
Neuromodulators
- e.g. Serotonin
(mins-hrs?)
- alter input-output
properties of spinal
neurons
Other exercise related
factors - e.g. motivation
- individual and context
specific effects
Fig. 2. Schematic illustration highlighting some key neuromuscular responses
to exercise. Various physiological processes that are affected by fatigue are
identified in bold lettering, with the approximate time course of their recovery
(or return to baseline) indicated in parentheses. Additional information about
the mechanism by which physiological changes impair function is provided
where possible. MN, motoneuron.
1071Recovery of Central and Peripheral Fatigue • Carroll TJ et al.
J Appl Physiol • doi:10.1152/japplphysiol.00775.2016 • www.jappl.org
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maximal contractions. This may be related to the observation
that central fatigue contributes proportionally more to the total
force reduction during sustained submaximal than maximal
contractions. For example, impaired voluntary activation ac-
counts for ~65% of the reduced MVC during 70 min of elbow
flexion at 5% MVC (88), ~40% of the MVC drop during 43
min of contraction at 15% MVC (89), but only ~25% of the
force drop for a 2 min MVC (100).
There is likely to be some maintenance of muscle perfusion
during submaximal contractions, depending on the target force,
and duty cycle when contractions are intermittent, which
should reduce the accumulation of metabolites that leads to
both firing of the subset of group III and IV afferents that are
sensitive to noxious stimuli and t-tubule depolarization by K
⫹
.
Accordingly, resting twitches evoked by motor nerve stimula-
tion do not recover appreciably within 20–30 min after sus-
tained, weak contractions of the elbow flexors (88, 89) (see
Fig. 1B), suggesting that mechanisms of peripheral fatigue in
such conditions relate mainly to impaired intracellular Ca
2⫹
handling or sensitivity.
Despite slow recovery of evoked twitch forces, MVC force
typically shows rapid, but partial, recovery within the first few
minutes after termination of sustained submaximal contrac-
tions. Voluntary activation measured by motor nerve or motor
cortical stimulation has a correspondingly rapid initial recovery
component but may not return to prefatigue levels until 20 –30
min postexercise (46, 47, 88, 89, 104, 105) (Fig. 1C). Per-
ceived effort, measured during brief efforts, takes ~5 min to
recover fully (80) but has not often been documented. Thus,
although the initial, partial restoration of voluntary force after
sustained low force contractions is likely due to central fatigue
recovery, impaired voluntary activation persists for longer after
submaximal contractions sustained for 6 –70 min than after
maximal contractions sustained for up to 2 min. The mecha-
nism underlying this delayed central recovery is not known.
Recovery from Locomotor Exercise
Sustained contractions at a single joint are a convenient
model to study fatigue and involve physical demands that are
similar to some activities of daily living (e.g., holding a bag of
groceries). However, there is uncertainty about the degree to
which the processes that constitute fatigue in such tasks also
apply to activities such as walking, running, and cycling, which
typically require higher rates of energy use, and consequently
greater cardiovascular and ventilatory demands. There is an
extensive literature on the physiological responses to fatiguing
locomotor exercise (see Refs. 37, 62, 66, 84 for reviews), but
direct measurement of muscle fatigue is challenging in such
tasks because it is difficult to measure force-generating capac-
ity during and immediately after exercise: there is typically
some delay required to couple subjects to a myograph and
initiate neuromuscular recording and stimulation. Nonetheless,
muscle fatigue has been documented after running (55, 58, 65,
78, 80, 95, 101), cycling (4, 5, 7–12, 15, 20, 33, 35, 38, 43, 44,
54, 56, 67, 68, 79, 83, 85, 94, 96, 97), and skiing (63) of
durations ranging from a few minutes to multiday ultraendur-
ance events (see also Refs. 13, 62 for review). Care is needed
Table 1. Summary of central and peripheral fatigue responses to exercise and recovery, categorized by modality, duration,
and intensity of exercise
Peripheral Fatigue Central Fatigue
Exercise Modality
Sustained MVC Sustained MVC
metabolite accumulation (e.g., K
⫹
)
2 VA due to group III/IV firing
fast recovery with re-perfusion (⬍30 s) fast recovery with reperfusion (⬍90 s)
Intermittent Shortening/Isometric Intermittent Shortening/Isometric
less blood occlusion and K
⫹
build-up
2 VA and recovery time course depends on exercise duration
slower recovery due to [Ca
2⫹
]
i
effects (min to h)
can vary from 1 to 30⫹ min
Lengthening Lengthening
damages muscle fibers muscle damage leads to 2 VA*
slow recovery (days to weeks) slow recovery (days)
Exercise Duration
Short Duration (<2–3 min) Short Duration (<2–3 min)
metabolite accumulation crucial (e.g., K
⫹
)
short lasting 2 VA (⬍90 s)
fast recovery with reperfusion (⬍30 s) 2 MN responsiveness (min)
Long Duration (>6 min) Long Duration (>6 min)
recovery depends on number of high [Ca
2⫹
]
i
episodes (intensity and duration)
recovery appears closely related to duration (mechanisms unknown)
[Ca
2⫹
]
i
effects can last min to h
can vary from 1 to 30⫹ min
glycogen depletion possible (h)
Exercise Intensity
High (near MVC/sprints) High (near MVC/sprints)
all muscle fibers recruited 2 VA due to group III/IV firing
metabolite accumulation crucial (e.g., K
⫹
)
fast recovery with reperfusion (⬍90 s)
fast recovery with reperfusion (⬍30 s) responsiveness of all MNs reduced
Low (low forces/endurance exercise) Low (low forces/endurance exercise)
low threshold, fatigue-resistant units 2 VA occurs if duration long
recovery depends on duration recovery can vary from 1 to 30⫹ min
low threshold MN excitability 2 (min)
VA, voluntary activation; MN, motoneuron. *Note that VA was reduced for more than 1 day after eccentric exercise when measured with motor nerve
stimulation, but not motor cortical stimulation (73). The reason for this discrepancy is not clear, but it illustrates that different measures of VA do not always
respond in the same way during fatigue and recovery.
1072 Recovery of Central and Peripheral Fatigue • Carroll TJ et al.
J Appl Physiol • doi:10.1152/japplphysiol.00775.2016 • www.jappl.org
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