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Fatigue measured in dynamic vs. isometric modes after trail running races of various distances.

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Purpose: Fatigue has previously been investigated in trail running by comparing maximal isometric force before and after the race. Isometric contractions may not entirely reflect fatigue-induced changes, so that dynamic evaluation is warranted. The aim of the present study was to compare the magnitude of the decrement of maximal isometric force vs. maximal power, force and velocity after trail running races ranging from 40- to 170-km. Methods: Nineteen trail runners completed races shorter than 60 km (SHORT) and 21 runners completed races longer than 100 km (LONG). Isometric maximal voluntary contractions (IMVC) of knee extensors (KE) and plantar flexors (PF) and maximal 7-s sprints on a cycle ergometer were performed before and after the event. Results: Maximal power output (Pmax; -1411%, p<0.001), theoretical maximum force (F0; -1114%, p<0.001) and theoretical maximum velocity (V0; -38%, p=0.037) decreased significantly after both races. All dynamic parameters but V0 decreased more after LONG than SHORT (p<0.05). Although the changes in IMVC were significantly correlated (p<0.05) to the changes in F0 and Pmax, reductions in IMVC for KE (-2916%, p<0.001) and PF (-2613%, p<0.001) were larger (p<0.001) than the reduction in Pmax and F0. Conclusions: After a trail running race, reductions in isometric vs. dynamic forces are correlated yet they are not interchangeable since the losses in isometric force were two to three time greater than the reductions in Pmax and F0. This study also shows that the effect of race distance on fatigue measured in isometric mode is true when measured in dynamic mode. Keywords: isometric maximal voluntary contraction, dynamic exercise, neuromuscular fatigue assessment, power-force-velocity profile.
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Fatigue Measured in Dynamic Versus Isometric Modes
After Trail Running Races of Various Distances
Jerome Koral, Marie Fanget, Laurianne Imbert, Thibault Besson, Djahid Kennouche, Audrey Parent,
Clément Foschia, Jérémy Rossi, and Guillaume Y. Millet
Purpose:Fatigue has previously been investigated in trail running by comparing maximal isometric force before and after the
race. Isometric contractions may not entirely reect fatigue-induced changes, and therefore dynamic evaluation is warranted.
The aim of the present study was to compare the magnitude of the decrement of maximal isometric force versus maximal
power, force, and velocity after trail running races ranging from 40 to 170 km. Methods:Nineteen trail runners completed
races shorter than 60 km, and 21 runners completed races longer than 100 km. Isometric maximal voluntary contractions
(IMVCs) of knee extensors and plantar exors and maximal 7-second sprints on a cycle ergometer were performed before and
after the event. Results:Maximal power output (P
max
;14% [11%], P<.001), theoretical maximum force (F
0
;11% [14%],
P<.001), and theoretical maximum velocity (3% [8%], P= .037) decreased signicantly after both races. All dynamic
parameters but theoretical maximum velocity decreased more after races longer than 100 km than races shorter than 60 km
(P<.05). Although the changes in IMVCs were signicantly correlated (P<.05) with the changes in F
0
and P
max
, reductions
in IMVCs for knee extensors (29% [16%], P<.001) and plantar exors (26% [13%], P<.001) were larger (P<.001) than
the reduction in P
max
and F
0
.Conclusions:After a trail running race, reductions in isometric versus dynamic forces were
correlated, yet they are not interchangeable because the losses in isometric force were 2 to 3 times greater than the reductions
in P
max
and F
0
. This study also shows that the effect of race distance on fatigue measured in isometric mode is true when
measured in dynamic mode.
Keywords:isometric maximal voluntary contraction, dynamic exercise, neuromuscular fatigue assessment, power-force-velocity
prole
Neuromuscular fatigue is usually dened as an exercise-
induced decrease in the maximal isometric force and/or power
output.
1
Yet, physical activities and sport performance such as trail
running not only are based on the capacity to generate isometric
forces but often depend on dynamic parameters such as power
output. Maximal power output reects the ability of athletes
neuromuscular system to generate high levels of force and produce
this force at high contraction velocity.
2
This ability of the neuro-
muscular system to produce power can be evaluated and charac-
terized by parabolic powervelocity and linear forcevelocity
relationships during a single all-out sprint.
3
Whereas, the power
forcevelocity prole (PFVP) has widely been investigated in
athletes,
46
including in recreational marathon runners,
7
to indi-
vidualize training and optimize performance, and it has more rarely
been used in the context of fatigue. Nevertheless, some studies
used PFVP to investigate fatigue due to strength training, that
is, the acute effects of different fatigue protocols
8
or the effects
of 3 interset rest intervals on PREPOST exercise changes
in PFVP.
9
Since 2003, the town of Chamonix (France) welcomes
thousands of mountain trail runners annually to compete in
different races ranging from 40 to 170 km. Previous studies
showed that neuromuscular fatigue, measured as an exercise-
related decrease in isometric maximal voluntary contraction
(IMVC), is greatly impacted by those races.
10,11
The reasons
why most scientists use the decrement in IMVC as a fatigue
index
1214
is likely due to the simplicity of its measurement.
Nonetheless, Cheng and Rice
15
showed that the assessment of
IMVC is related to some but not all impairments in neuromuscular
function following dynamic exercise. Various studies,
16,17
includ-
ing some recent investigations from our group,
18,19
also
highlighted that measurements of velocity and power provide
additional information on the etiology of neuromuscular fatigue
induced by dynamic tasks. For example, Krüger et al
19
reported
that IMVC and maximal power output (P
max
) are both indicative
of neuromuscular fatigue, yet depending on the duration and
intensity of exercise, the decrease in IMVC may be greater than
P
max
or vice versa. Thus, they are not interchangeable. Indeed,
these authors
19
suggested that the peripheral changes explaining
the decrease in IMVC are likely attributed to changes within the
muscle, such as a decrease in myoplasmic Ca
2+
concentration
and/or Ca
2+
sensitivity while changes in PFVP would be more
related to metabolic disturbance (ie, increased ADP concentration
and/or decreased ATP concentration) affecting for instance the
rate of cross-bridge dissociation. In addition, Morel et al
20
showed
that low velocity and isometric contractions resulted in a greater
voluntary activation (VA) inhibition (ie, central fatigue) as com-
pared with higher velocity dynamic contractions. This may also
have an effect during testing.
Koral, Imbert, Besson, Kennouche, Rossi, and Millet are with the Laboratoire
Interuniversitaire de Biologie de la Motricité, and Fanget, the Laboratoire SNA-
EPIS, Univ Lyon, UJM-Saint-Etienne, Saint-Etienne, France. Parent is with the
Dept of Biological Sciences, Université du Québec à Montréal (UQÀM), Montreal,
QC, Canada, and CHU Sainte-Justine (CRME) Montréal, QC, Canada. Foschia is
with the Dept of Clinical and Exercise Physiology, Sports Medicine Unit, Faculty of
Medicine, University Hospital of Saint-Etienne, Saint-Etienne, France. Millet is also
with the Inst Universitaire de France, Paris, France. Millet (guillaume.millet@univ-
st-etienne.fr) is corresponding author.
1
International Journal of Sports Physiology and Performance, (Ahead of Print)
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In Krüger et al,
19
the longest fatiguing exercise duration was
90 minutes. Hence, the effect of prolonged (eg, marathon) versus
extreme (ultramarathon) duration tasks on neuromuscular fatigue
measured using both isometric (IMVC) and dynamic (PFVP)
parameters remains unknown. Comparing the effects of prolonged
running exercise of varying distances on IMVC and PFVP could
help to provide more comprehensive insight into the etiology of
neuromuscular fatigue following mountain trail running. Accord-
ingly, the aim of the present study was to compare the magnitude of
the decrement of IMVC versus PFVP parameters (ie, P
max
, theo-
retical maximum force [F
0
] and theoretical maximum velocity
[V
0
]) measured during sprint cycling after trail running races
ranging from 40 to 170 km. More specically, we wanted to
test 3 hypotheses: (1) based on a previous study,
19
the loss in
P
max
is mostly explained by a decrease in F
0
rather than a decrease
in V
0
, (2) since the distance of the running exercise induces
signicant fatigue that negatively affects force
21
thus IMVC and
potentially F
0
/P
max
, the amplitude of the change in PFVP is
dependent on the distance (SHORT vs LONG), (3) a strong
correlation exists between the changes in IMVC and the changes
in F
0
.
Methods
Participants
Out of the 75 runners (49 males and 26 females) who voluntarily
participated in this study, 40 (24 males and 16 females) were able to
complete the testing (Figure 1). They were all registered to one of
the different races of the Ultra-Trail du Mont-Blanc, ranging from
40 km and ± 2300 m of elevation to 170 km and ± 10,000 m
(Table 1). Races were subsequently classied into SHORT (less
than 60 km: Martigny-Combe à Chamonix and OrsièresChampex
Chamonix) and LONG (more than 100 km: Courmayeur
ChampexChamonix, Sur les Traces des Ducs de Savoie, and
Ultra-Trail du Mont-Blanc) distances. Three participants reported
that they ran the entire race with a slower runner (partner or friend)
and did not attempt to complete the race as quickly as possible
during the last 10 km and thus were excluded from the study. All
participants were trained and were not suffering from any chronic
metabolic and muscle diseases. Their characteristics are presented in
Table 1. Written and verbal explanations of the experimental
protocol and associated risks were provided to all participants before
obtaining written informed consent. Ethical approval has been
obtained from the French Ethical Research Committee (CPP Ouest
VI, ethics committee agreement 19.03.14.41740 received on 05/02/
2019) and the study has been registered to ClinicalTrials.gov
(NCT04025138).
Experimental Design
This study was part of a larger study investigating the effect of trail
and ultra-trail racing on various physiological and biomechanical
responses in men and women. Each participant completed one
familiarization and 2 experimental sessions. Participants rst vis-
ited our laboratory 5 to 8 weeks before the race to be familiarized
Figure 1 CONSORT study ow diagram. CONSORT indicates CONsolidated Standards of Reporting Trials; LONG, races longer than 100 km;
POST, after; PRE, before; SHORT, races shorter than 60 km.
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Table 1 Characteristics of the Races and Participants
Race Our classification Distance, km D+, m ITRA category Time (minmax), min Participants (M/F) Age, y Height, m Mass, kg
MCC SHORT 40 2300 S 265585 5/5 36.3 (9.2) 1.73 (0.08) 65.4 (10.7)
OCC 55 3500 M 378746 6/3 36.6 (7.5) 1.75 (0.08) 71.1 (15.2)
CCC LONG 101 6100 XL 9261576 8/3 36.6 (9.2) 1.75 (0.09) 68.9 (9.0)
TDS 145 9100 XXL 14842662 1/1 39.5 (6.4) 1.66 (0.15) 56.2 (13.4)
UTMB 170 10,000 XXL 17312168 5/3 37.8 (7.0) 1.71 (0.11) 63.2 (10.9)
Abbreviations: CCC, CourmayeurChampexChamonix; F, female; ITRA, International Trail Running Association; LONG, races longer than 100 km; M, male; max, maximum; min, minimum; MCC, Martigny-Combe à
Chamonix; OCC, OrsièresChampexChamonix; SHORT, races shorter than 60 km; TDS, Sur les Traces des Ducs de Savoie; UTMB, Ultra-Trail du Mont-Blanc.
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with the experimental settings. Subsequently, 2 to 3 days before
the race, participants visited the on-site laboratory (National School
of Ski & Mountaineering, Chamonix, France) to perform PRE
tests. Finally, within 60 (15) minutes of nishing the race, they
completed the POST tests and were asked to rate their fatigue and
muscle pain in knee extensor (KE) and plantar exor (PF) muscles.
Familiarization Session. After a medical examination and a
maximal incremental test on a treadmill, participants performed
2 maximal 7-second duration sprints on cycle ergometer (Monark,
Vansbro, Sweden) separated by a 2-minute rest period. The
resistance was set to 0.5 N·kg
1
of body mass and 0.7 N·kg
1
of body mass, for the rst and second sprints, respectively.
Afterward, they sat on an isometric knee dynamometer, and
subsequently on a custom-built PF dynamometer, and were famil-
iarized with IMVC measurements of the KE and PF. Participants
were instructed to contract as strongly as possible for 4 seconds
during IMVCs.
PRE-Race Tests. Contrary to the familiarization session, and in
order to efciently record IMVCs, all participants rst performed a
standardized warm-up of 10 submaximal isometric contractions,
one near maximal contraction, and subsequently 3 KE IMVC and
3 PF IMVC. All attempts were separated by 30-second rest
(Figure 2). Next, two 7-second sprints with 120-second rest
were performed on the cycle ergometer with the same resistances
as in the familiarization session.
POST-Race Tests. The KE IMVC and PF IMVC of the nishers
were tested on the same ergometers as in PRE. Regarding the
PFVP, the friction loads were reduced to 0.35 and 0.5 N·kg
1
of
body mass for the rst and second sprints, respectively, in order to
take into account the anticipated 30% to 35% reduction in maximal
force production capacity due to fatigue caused by the race.
10,22
PRE and POST resistances were chosen to cover a wide range of
velocities and allow the subjects to reach their P
max
.
23
Data Collection
The PFVP Recordings. All features of the equipment were
described in previous studies.
24,25
The Monark cycle ergometer
was made up of a strain gauge (FN 3030 type; FGP Instrumenta-
tion, Les Clayes-sous-Bois, France) to measure the friction force
and an optical encoder (100 pts/turn, Hengstler type RI 32.0;
Aldingen, Germany) to quantify the ywheel displacement.
Data were sampled at 200 Hz, recorded in LabVIEW software
(NI, Austin, TX) and were ltered with a fourth-order low-pass
Butterworth lter at 12 Hz.
Figure 2 (A) Experimental protocol, (B) evaluation of KE, and (C) evaluation of PF. Warm-up was not performed during POST sessions. IMVC
indicates isometric maximal voluntary contractions; KE, knee extensors; PF, plantar exors; POST, after.
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The saddle height was adjusted to allow the participants to
fully extend the leg once seated with the heel on the pedal, and was
kept the same for all sessions. Toe clips were well fastened to avoid
foot displacement from the pedal. Participants started each trial
with right pedal at 45° from the vertical axis and to remain seated at
all time. For each trial, participants were vigorously encouraged to
pedal as fast as possible during the entire sprint.
Isometric Force Recordings. The KE torque was measured on
an isometric knee dynamometer (ARS dynamometry; SP2 Ltd,
LjubIjana, Slovenia) with the hips and the right knee at 90° of
exion (with 0° referring to the extended neutral position). PF
torque was measured by an instrumented pedal (CS1060 300 Nm;
FGP sensors, Les Clayes-sous-Bois, France). Participants were
seated in a custom-built chair with right hip, knee, and ankle angles
of 90°. The chest was strapped to the chair and heel and forefoot
were securely xed to the pedal with noncompliant straps to avoid
displacement of the foot during IMVC. All data were recorded and
analyzed using LabChart 8 Software (ADInstruments, Bella Vista,
Australia).
Electrical Nerve Stimulation. Single electrical stimuli were deliv-
ered via constant-current stimulator (DS7A; Digitimer, Welwyn
Garden City, Hertfordshire, United Kingdom) to both the right
femoral (pulse width: 1 ms) and the tibial (pulse width: 0.2 ms)
nerves for KE and PF, respectively. Maximal output voltage was
400 V. Stimulationof the femoral nerve were delivered via a 30-mm
diameter surface cathode manually pressed into the femoral triangle
(Meditrace 100) and a 10 ×5 cm self-adhesive stimulation electrode
(Medicompex SA, Ecublens, Switzerland) located in the gluteal fold
(Figure 2B). Stimulation of the tibial nerve was delivered via a
bipolar bar stimulating electrode with 30-mm anodecathode spac-
ing (Bipolar Felt Pad Stimulating Electrode part no. E.SB020/4 mm;
Digitimer) placed on the popliteal fossa and parallel to the nerve
(Figure 2C). To determine the optimal intensity of stimulation,
single stimuli were delivered incrementally in relaxed muscle until
the force response plateaued. To ensure supramaximality, a stimulus
intensity of 130% of the intensity to produce the maximal twitch
responses was used. Stimulus intensity was determined at the
beginning of each session.
Data Analysis
PowerForceVelocity Prole. In order to be consistent with
neuromuscular tests, only the right leg was analyzed. All partici-
pants who did not reach a coefcient of determination R
2
>.85 in
forcevelocity relationship were excluded from the study.
The range of velocity data was set between 0% and 98% of
maximal velocity. P
max
was dened using F
0
and V
0
26
:
Pmax =ðF0×V0Þ
4,
where F
0
and V
0
represent the 2 extremes of the FV spectrum and
characterize the dynamic force production capabilities at low and
high velocities, respectively.
27
The slope of FV relationship (S
FV
) was computed as:
SFV =
F0
V0
:
The power output (P; in Watts) produced at each pedal stroke
during the sprint was computed as presented in Fanget et al
28
by
using the friction force (F
frict
), the inertial force (F
inert
) and the
ywheel linear velocity (V):
P=ðFfrict þFinertÞ×V:
The linear relationship obtained by free deceleration of the ywheel
allowed to dene the inertia.
24
PREPOST variations of all
dynamic parameters, that is, P
max
(ΔP
max
), F
0
(ΔF
0
), V
0
(ΔV
0
)
and S
FV
(ΔS
FV
) were calculated.
Isometric Forces. The maximal torque values were determined as
the highest peak torque recorded from the contractions (out of the 3
IMVCs for PF and KE). PREPOST variations of KE (ΔKE), PF
(ΔPF), and KE + PF as a surrogate of the lower limb extensors force
production (ΔKE + PF obtained by summing the 2 torques at PRE and
comparing it to the sum of those 2 torques at POST) were calculated.
Electrical Nerve Stimulation. During the last 2 IMVCs for KE
and PF, a superimposed high frequency doublet (Db100) was
delivered on the force plateau. Afterward, the relaxed muscle
was stimulated by resting Db100 and a single twitch (Pt). ΔPt
was used as an index of peripheral fatigue. Percentage of VA was
then assessed with the conventional ratio of the superimposed
Db100 over the size of the control Db100:
VA =1superimposed Db100
resting Db100 ×100:
Statistical Analysis
All data were reported as the mean (SD). Linear forcevelocity
relationships were plotted under least squares regressions. All
statistical tests were performed using Statistica (version 8; StatSoft,
Inc, Tulsa, OK). Data were checked for normality and homogeneity
of variances using ShapiroWilk and Levene tests, respectively.
The effect of race distance on change in PFVP and IMVC
parameters was tested using a 2-way repeated-measures analysis
of variance, that is, distance (LONGSHORT) ×time (PRE
POST). Main and interaction effects were followed up with the
NewmanKeuls post hoc pairwise comparisons when appropriate.
The relationships between the PFVP parameters, distance, running
time, and IMVC (PF and KE) were investigated by computing the
Pearson correlation coefcients. When the normality and variance
homogeneity assumptions were not satised, the nonparametric
tests, Wilcoxon for PREPOST comparisons, MannWhitney for
SHORTLONG comparisons, and Spearman for correlations (ρ),
were preferred. The PREPOST differences for SHORT and
LONG distances were compared using a Student test. The thresh-
old to reject the null hypothesis was set at P<.05. Effect size was
calculated using partial eta square (η2
p).
Results
At PRE, P
max
of participants was 669.8 (185.9) W (range = 289
1112 W), F
0
was 122.6 (28.4) N (range = 70192 N), and V
0
was
21.7 (2.1) m·s
1
(range = 16.526.3 m·s
1
). P
max
,F
0
,V
0
, and
S
FV
were not signicantly different between SHORT and LONG
(P= .687, P= .981, P= .359, and P= .651, respectively).
At POST, 5 participants from LONG races did not reach a R
2
value higher than .85 (range = .08.77) and were thus excluded.
Changes in PFVP
There was a signicant time effect for all PFVP variables, that is,
P
max
(14% [11%], P<.001, η2
p=.59), F
0
(11% [14%], P<.001,
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η2
p=.39), V
0
(3% [8%], P= .037, η2
p=.12), and S
FV
(8% [18%],
P= .037, η2
p=.19) decreased signicantly from PRE to POST. F
0
,
P
max
, and S
FV
showed a signicant distance ×time interaction
(P= .025, η2
p=.13; P= .047, η2
p=.10; P= .032, η2
p=.12, respec-
tively). Post hoc tests showed a signicant decrease in P
max
between PRE and POST for both SHORT and LONG (9%
[9%], P<.001 and 19% [11%], P= .008, respectively). The
decrease in P
max
was signicantly greater for LONG than SHORT
(P= .008). F
0
and S
FV
decreased signicantly in LONG (17%
[14%], P<.001 and 15% [19%], P= .004, respectively) but not in
SHORT (5% [11%], P= .059 and 1% [14%], P= .687, respec-
tively; Figure 3).
The ΔP
max
was correlated to ΔF
0
(ρ= .908, P<.001; Figure 4A)
and ΔS
FV
(ρ= .802, P<.001) but not to ΔV
0
(ρ=.129, P= .426;
Figure 4B).
Isometric Force Parameters
There was a time effect for both KE (28% [16%], P<.001,
η2
p=.69) and PF (24% [16%], P<.001, η2
p=.77) IMVCs but
distance ×time interaction did not reach signicance for these
variables (P= .085 and P= .067, respectively). There were both
time effect (28% [14%], P<.001, η2
p=.77) and distance ×time
interaction (P<.05, η2
p=.11) for KE + PF IMVC. Signicant
correlations were found between dynamic properties and isometric
force parameters (Table 2). In particular, ΔKE + PF was correlated
with ΔP
max
(ρ=.612,P<.001; Figure 4C), ΔF
0
(r=.665,P<.001;
Figure 4D)andΔS
FV
(r=.656, P<.001) but not with ΔV
0
(r=.216; P=.572).
There was a time effect for both VA
KE
(P<.001, η2
p=.43) and
VA
PF
(P<.001, η2
p=.42) but there was no distance ×time inter-
action for these variables. Similarly, both Pt
KE
and Pt
PF
showed a
time effect (P<.001, η2
p=.68 and η2
p=.49, respectively) but the
distance ×time interaction was not reached for this parameter either
(P= .058 for Pt
KE
and P= .821 for Pt
PF
and P= .056 for Pt
KE+PF
).
Discussion
The aims of the present study were to measure the effects of fatigue
induced by prolonged running exercises on dynamic neuromuscu-
lar properties and to investigate whether or not this differs from
classicneuromuscular fatigue measures, that is, in isometric
mode. The main ndings were that (1) all dynamic parameters
decreased signicantly after the race but the changes were more
pronounced for P
max
and F
0
than V
0
; (2) all PFVP parameters but
V
0
decreased more after LONG than SHORT; (3) the changes in
Figure 3 (A) P
max
, (B) F
0
, (C) V
0
, and (D) S
FV
measured PRE and POST trail running races. Values are presented as mean (SD) and individual data
of each participant. F
0
indicates theoretical maximum force; LONG, races longer than 100 km; P
max
, maximal power; POST, after; PRE, before; S
FV
,
slope of forcevelocity relationship; SHORT, races shorter than 60 km; V
0
, theoretical maximum velocity. *Signicant difference at P<.01. **Signicant
difference at P<.001. $Signicant distance ×time interaction.
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Figure 4 Correlations for short and long distances (A) between ΔP
max
and ΔF
0
, (B) between ΔP
max
and ΔV
0
, (C) between ΔP
max
and ΔKE + PF, and (D) between ΔF
0
and ΔKE + PF. ΔF
0
indicates PREPOST variations of theoretical maximum force; KE, knee extensors; ΔKE + PF, PREPOST variations of KE + PF maximal isometric force; LONG, races longer than 100 km; ΔP
max
,
PREPOST variations of maximal power; PF, plantar exors; POST, after; PRE, before; SHORT, races shorter than 60 km; ΔV
0
, PREPOST variations of theoretical maximum velocity.
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isometric force were signicantly correlated to dynamic force and
maximal power, but the reduction in IMVC were approximately
twice as great as the reductions in P
max
and F
0
. Overall, these
ndings suggest that the decreases in isometric versus dynamic
forces due to fatigue induced by trail running are related, yet they
are not interchangeable.
Effects of Fatigue Due to Trail Running of Various
Distances on Dynamic Neuromuscular Properties
This study is the rst to compare parameters derived from PFVP
following prolonged running exercise of varying durations (518
[140] min vs 1750 [618] min). An original nding of the present
work is that P
max
and F
0
were directly and differently affected by
race distance (Figure 3A and 3B), while V
0
barely declined and
showed no distance ×time interaction. Indeed, losses in P
max
and
F
0
were 2 (for P
max
) to 3 (for F
0
) times as elevated in LONG (19%
and 17%, respectively) than in SHORT (9% and 5%, respec-
tively) races (P<.01).
The loss in P
max
was mainly due to a reduction in F
0
rather
than a loss in V
0
as shown by the high (r>.85) coefcient of
correlation between ΔP
max
and ΔF
0
(Figure 4A) and the similar
magnitude of change for P
max
(14%) and F
0
(11%). On the
contrary, no correlation was found between ΔV
0
and ΔP
max
(Figure 4B) and V
0
barely, while signicantly, declined (3%).
This nding was in line with the study of Krüger et al
19
that did not
observe any V
0
decrease after a prolonged cycling exercise, that is,
P
max
was also mainly affected by F
0
. Although the present study
does not allow to determine why the change in power output
depends almost exclusively on F
0
, possible explanations can
rst be found in central alterations. Indeed, Morel et al
20
reported
that low velocity and isometric contractions (ie, higher force
production) were associated with higher central fatigue (higher
VA inhibition) when high-velocity contractions induced more
peripheral fatigue (larger changes in contractile properties). The
reasons why the change in power output depends more on F
0
could
also be related to what happens in the muscles. The moderate
decrease in V
0
(η2
p=.12) was expected in the present study as
Krüger et al
19
showed that V
0
was altered for brief and intense
rather than prolonged and low-intensity exercise, that is, the lower
the fatiguing exercise intensity, the lower the reduction in V
0
.These
authors suggested that the reduction in V
0
during intense exercise, in
which maximal power output was systematically reached, was due to
an increased concentration in ADP and/or a decreased concentration in
ATP resulting in a decrease rate of cross-bridge formation and a greater
fatigue in fast-twitch motor units. This was unlikely to occur in the
present study, as it is well known that trail running is submaximal and
mainly aerobic. Here, it can be speculated that F
0
(hence P
max
)
reduction was likely due to central alterations and to excitation
contraction coupling failure (ie, decreased Ca
2+
release by the sarco-
plasmic reticulum) due to glycogen depletion resulting from prolonged
and exhausting exercise.
29
This is in agreement with the decline in both
Pt
KE
and Pt
PF
(Table 3). Repeated eccentric contractions due to
downhill running may have induced muscle damage which could
have also negatively affected the contractility properties.
30
Fatigue in Dynamic Versus Isometric Modes
In the present study, trail running races induced not only a signicant
reduction in P
max
(see above), but also in IMVC in both KE and PF
after SHORT and LONG races (Table 3). A decreased IMVC was
expected as our group has consistently reported similar ndings over
the past 20 years.
10,11,3133
However, the present study performed a
novel comparison between isometric and dynamic measurements.
Contrary to Krüger et al,
19
longer and less intense exercise was
not associated with lower P
max
reduction since ΔP
max
was higher
for LONG than SHORT. This suggests that for prolonged exercise,
that is, when energy expenditure comes almost entirely from
oxidative metabolism, longer exercise leads to greater reduction
in P
max
and IMVC, possibly because force reductions measured in
isometric and dynamic modes share common mechanisms, in
particular central fatigue. Indeed, the correlation between ΔF
0
and ΔIMVC was signicant in the present study, in contrast to
the results reported by Krüger et al.
19
It is also worth mentioning
Table 2 Correlations Between Dynamic Properties and Isometric Force
Parameters
Parameter ΔP
max
ΔF
0
ΔV
0
ΔS
FV
ΔKE ρ= .518*** ρ= .511*** ρ=.215 ρ= .513***
ΔPF ρ= .529*** r= .443** ρ=.071 r= .394*
ΔKE + PF ρ= .612*** r= .665*** ρ=.216 r= .656***
ΔP
max SHORT
ΔF
0 SHORT
ΔV
0 SHORT
ΔS
FV SHORT
ΔKE
SHORT
r= .599** r= .606** r=.355 r= .567*
ΔPF
SHORT
r= .293 r= .210 r= .251 r= .133
ΔKE + PF
SHORT
r= .556* r= .529* ρ=.275 r= .472*
ΔP
max LONG
ΔF
0 LONG
ΔV
0 LONG
ΔS
FV LONG
ΔKE
LONG
ρ= .319 ρ= .479* ρ=.284 ρ= .509*
ΔPF
LONG
r= .509* r= .537* ρ=.311 r= .504*
ΔKE + PF
LONG
r= .480** r= .683*** ρ=.439 r= .714***
Abbreviations: ρ, Spearman correlation coefcients; ΔF
0
, PREPOST variations of theoretical maximum force; ΔKE, PRE
POST variations of knee extensors; ΔKE + PF, PREPOST variations of maximal isometric force KE + PF; LONG, races
longer than 100 km; ΔPF, PREPOST variations of plantar exors; ΔP
max
, PREPOST variations of maximal power;
SHORT, races shorter than 60 km; ΔV
0
, PREPOST variations of theoretical maximum velocity; ΔS
FV
, PREPOST
variations of the slope of FV relationship; r, Pearson correlation coefcients.
*Signicant differences at P<.05. **Signicant differences at P<.01. ***Signicant differences at P<.001.
8Koral et al
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that the longer the race, the greater the correlation between IMVC
and F
0
(see Table 2).
However, similar to Krüger et al,
19
after 90 minutes of cycling
at moderate intensity, IMVC (over 25%) decreased more than
P
max
(14%) after trail running races (SHORT and LONG pooled).
The present results strengthen Krügers hypothesis concerning
differences between isometric and dynamic modes which suggest
that these indexes of fatigue do not entirely share the same
physiological mechanisms and, as such, are not interchangeable.
As stated above, ΔP
max
and ΔF
0
but not ΔV
0
were affected by
race distance. There was also a distance ×time interaction for KE +
PF IMVC although the 2 to 3 times greater changes in LONG than
in SHORT for ΔP
max
and ΔF
0
were not found for ΔIMVC as it was
only 50% higher for LONG in isometric mode. Also, there were no
signicant differences between SHORT and LONG for VA
KE
and
VA
PF
(Table 3) so that the greater P
max
and F
0
reduction in LONG
were caused by central fatigue as anticipated based on previous
research in ultra-trail exercise.
10,11
The distance ×time interaction
did not reached signicance for peripheral fatigue either (eg, P=
.056 for Pt
KE+PF
). Interestingly, some correlations with ΔKE versus
ΔPF differed between SHORT and LONG (Table 2). For instance,
ΔKE was signicantly correlated with ΔP
max
and ΔF
0
in SHORT
whereas ΔPF was not. On the opposite, ΔPF was signicantly
correlated with ΔP
max
and ΔF
0
in LONG; whereas, ΔKE was only
correlated with ΔF
0
. The reasons for these differences are not clear
(eg, there were no effects of using poles or not) and still need to be
investigated.
This study does not come without limitations. First, as the
present data are part of a larger study, there was a delay of 60
(15) minutes between the end of the race and the postrace assess-
ment. Yet the measurements of dynamic and isometric properties
were taken in close temporal proximity (510 min); although, the
participants always started with isometric contractions. Second,
other testing methods to characterize the PFVP of our participants
could have been used. Yet, as trail runners are not used to perform
SJ, CMJ, or sprint, and because our main concern was to avoid our
participants from getting injured, we decided to use the cycle
ergometer with the 2-point method recommended by Garcia-
Ramos et al.
34
It allowed us to increase the number of points
for the FV relation as each resistance would extend the total pool of
data. Nevertheless, because of the specicity of our participants, we
had to use medium values (0.50.7 N·kg
1
) which could compro-
mise the precision of the forcevelocity prole and are less reliable
than 0.4 to 1.0 N·kg
1
as described by Garcia-Ramos et al.
34
Third,
the determination of the 2 friction loads at POST was based on the
results of previous studies on IMVC decrement after ultra-trail
running. In the future, loads must be individualized based on
reduction in IMVC or P
max
measured during a rst sprint.
23
Practical Applications
When attempting to assess the etiology of fatigue in athletes, the
present paper suggests that it would be a limited approach to only
focus on IMVC, and that integrating PFVP allows a more holistic
insight into neuromuscular function, while also being more represen-
tative of multijoint dynamic performance, such as running. Since both
types of evaluation are fast and easy to perform, we suggest that
scientists and coaches integrate isometric and dynamic measurements,
that is, isometric maximal voluntary contraction and PFVP, to better
quantify/understand acute and chronic fatigue. This is an important
consideration in the context of training and fatigue monitoring.
Conclusions
The present study brings important insight into fatigue etiology in trail
running from short (50 km) to longer (up to 170 km) trail running
races. Our ndings indicate that all PVFP parameters decreased after
the race, yet the effect of distance differs between the PVFP variables
since the magnitude of losses was greater in LONG than in SHORT
for P
max
and F
0
but not for V
0
.ThelossinP
max
was mostly explained
by a decrease in F
0
. Finally, it is concluded that while P
max
,F
0
,and
IMVC are strongly correlated, they are not interchangeable as the
magnitude of their changes was different, that is, isometric and
dynamic measurements identify distinct fatigue responses.
Acknowledgments
The authors would like to thank the Saint-Etienne University Hospital, the
organizers of the Ultra-Trail du Mont Blanc, the National School of Ski &
Mountaineering for logistical support and all the participants. The authors
also acknowledge the technical help provided by Dr Diana Rimaud and
Prof Léonard Féasson as well as Dr Pierre Samozino for his scientic
contribution and Dr Callum Brownstein for providing suggestions on the
manuscript. This study was funded by an IDEX Lyon fellowship.
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KE PF KE + PF
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SHORT
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PNS
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Fatigue in Trail Running: Isometric vs Dynamic Evaluation 11
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... Many physiological changes occur during and at the end of the races (Baiget et al., 2018;Carmona et al., 2019;Koral et al., 2022;Pradas et al., 2021;Roca, 2019). Dehydration processes and neuromuscular fatigue, especially occurring in the lower limb (Roca, 2019), have been observed (Baiget et al., 2018;Carmona et al., 2019;Koral et al., 2022;Pradas et al., 2021;Roca, 2019). ...
... Many physiological changes occur during and at the end of the races (Baiget et al., 2018;Carmona et al., 2019;Koral et al., 2022;Pradas et al., 2021;Roca, 2019). Dehydration processes and neuromuscular fatigue, especially occurring in the lower limb (Roca, 2019), have been observed (Baiget et al., 2018;Carmona et al., 2019;Koral et al., 2022;Pradas et al., 2021;Roca, 2019). The hydration status prior to competition and strategies for maintaining euhydration during it are important, given their potential to influence athletic performance (Gatterer, 2021). ...
... Despite the limited existing studies on ML-BIVA in the realm of sports, particularly in TR, muscle changes have been evaluated using various methods. Multiple studies have reported reductions in isometric maximum voluntary contractions (IMVC) of knee extensors and plantar flexors following TR races (Fourchet et al., 2012;Koral et al., 2022;Pastor et al., 2022;Temesi et al., 2021), with more pronounced effects observed in longer-distance events (Temesi et al., 2021). For instance, Koral et al. (2022) observed reductions of 16% in knee extensor IMVC and 13% in plantar flexor IMVC in TR races shorter than 60 km, which further increased to 29% and 26%, respectively, in races longer than 100 km. ...
Article
Full-text available
Background This study aims to investigate body fluids and muscle changes evoked by different trail races using anthropometric, bioelectrical, and creatine kinase (CK) measurements. Methods A total of 92 subjects (55 men, 37 women) participating in three different races of 14, 35, and 52 km were evaluated before (PRE) and after (POST) the races. Classic bioelectrical impedance vector analysis was applied at the whole-body level (WB-BIVA). Additionally, muscle-localized bioelectrical assessments (ML-BIVA) were performed in a subgroup of 11 men (in the quadriceps, hamstrings, and calves). PRE-POST differences and correlations between bioelectrical values and CK, running time and race distance were tested. Results Changes in whole-body vectors and phase angles disclosed an inclination towards dehydration among men in the 14, 35, and 52 km groups ( p < 0.001), as well as among women in the 35 and 52 km groups ( p < 0.001). PRE Z/H was negatively correlated with running time in the 35 km men group and 14 km women group ( r = −0.377, p = 0.048; r = −0.751, p = 0.001; respectively). POST Z/H was negatively correlated with running time in the 14 km women group ( r = −0.593, p = 0.02). CK was positively correlated with distance in men and women ( p < 0.001) and negatively correlated with reactance and vector length in the 14 km men group ( p < 0.05). ML-BIVA echoed the same tendency as the WB-BIVA in the 35 and 52 km runners, with the most notable changes occurring in the calves ( p < 0.001). Conclusions WB-BIVA and CK measurements underscored a conspicuous trend towards post-race dehydration and muscle damage, displaying a weak association with performance. Notably, ML-BIVA detected substantial alterations primarily in the calves. The study underscores the utility of BIVA as a technique to assess athlete’s body composition changes.
... Diverging responses in these capacities have been noted after specific fatiguing tasks like cycling at varying intensities [13]. In addition, after a running event, lower limb isometric force and maximal jump power decreased by~25-30% and 14%, respectively, with only a moderate correlation between the two [14]. Similarly, a significant decrease in knee extension and plantar flexion maximal force (22% and 17%, respectively) was observed after a marathon run, with no change in CMJ force [15]. ...
... Previous research has documented that the magnitude of fatigue is specific both to the fatiguing protocol and measurement tasks [13][14][15]28,29]. Therefore, our results were expected. ...
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Background: Strength and conditioning experts widely recognize the dynamic strength index (DSI) as a tool for assessing an athlete’s ability to utilize strength in dynamic actions. The DSI is calculated as the ratio of peak force in dynamic actions versus isometric ones. To date, the influence of fatigue on the DSI is still not fully understood. This study aimed to explore the effects of both dynamic and isometric fatigue tasks on the DSI. Methods: A total of 24 physically active participants underwent fatigue tests involving repeated countermovement jumps (dynamic) and repeated isometric mid-thigh pulls (isometric) in separate visits. Results: The results revealed a marked drop in performance, with dynamic force showing a more significant reduction (p < 0.001; d = 1.57) than isometric force (p = 0.015; d = 0.30). After the isometric fatigue task, the DSI increased, indicating a more substantial decline in isometric force (p < 0.001; d = 1.75) compared to dynamic force (p = 0.313; d = 0.08). Following this trend, the DSI decreased post-dynamic fatigue (p < 0.001; d = 0.99) and increased post-isometric fatigue (p < 0.001; d = 3.11). Conclusion: This research underscores the need to consider fatigue’s task-specific effects on the DSI, enabling more tailored training methodologies for athletes.
... The power-torque-velocity profile has already been investigated in athletes of different levels (21), including marathon runners (33), and has been linked to sprint running performance (30) but not to endurance running performance so far. Our group recently measured PTVP in a population of experienced but nonelite trail runners (22) with the aim to assess fatigue. Since lower-limb power has been suggested to be determinant in uphill TR performance (23), it would be interesting to analyze how the PTVP of trail runners could potentially discriminate between elite and nonelite. ...
... In other words, both muscle and neural adaptation to greater volume of endurance training may explain the lower velocity capacities (i.e., lower V 0 ) in ELITE compared with EXP. Our group recently reported PTVP data of experienced trail runners (24 males and 16 females) (22). For equivalent body mass, our group reported equivalent absolute maximal power compared with our EXP group and, interestingly, greater T 0 and lower V 0 compared with EXP ( Figure 3 in (22)). ...
Article
Besson, T, Pastor, FS, Varesco, G, Berthet, M, Kennouche, D, Dandrieux, P-E, Rossi, J, and Millet, GY. Elite vs. experienced male and female trail runners: comparing running economy, biomechanics, strength, and power. J Strength Cond Res 37(7): 1470-1478, 2023-The increased participation in trail running (TR) races and the emergence of official international races have increased the performance level of the world best trail runners. The aim of this study was to compare cost of running (Cr) and biomechanical and neuromuscular characteristics of elite trail runners with their lower level counterparts. Twenty elite (10 females; ELITE) and 21 experienced (10 females; EXP) trail runners participated in the study. Cr and running biomechanics were measured at 10 and 14 km·h-1 on flat and at 10 km·h-1 with 10% uphill incline. Subjects also performed maximal isometric voluntary contractions of knee and hip extensors and knee flexors and maximal sprints on a cycle ergometer to assess the power-torque-velocity profile (PTVP). Athletes also reported their training volume during the previous year. Despite no differences in biomechanics, ELITE had a lower Cr than EXP (p < 0.05). Despite nonsignificant difference in maximal lower-limb power between groups, ELITE displayed a greater relative torque (p < 0.01) and lower maximal velocity (p < 0.01) in the PTVP. Females displayed shorter contact times (p < 0.01) compared with males, but no sex differences were observed in Cr (p > 0.05). No sex differences existed for the PTVP slope, whereas females exhibited lower relative torque (p < 0.01) and velocity capacities (p < 0.01) compared with males. Although not comprehensively assessing all determining factors of TR performance, those data evidenced level and sex specificities of trail runners in some factors of performance. Strength training can be suggested to lower level trail runners to improve Cr and thus TR performance.
... De nombreuses études ont rapporté des déficits fonctionnels dépendants fortement de la tâche (Horita et al., 2003 ;Koral et al., 2021 ;Nicol et al., 1991c). Ce phénomène est connu sous le nom de « task dependency » en anglais (Enoka et Stuart, 1992 ;. La motivation du participant, le patron d'activation musculaire et les commandes motrices associées, l'intensité et la durée de l'exercice ainsi que la vitesse de contraction sont autant de paramètres qui apparaissent comme dépendant de la tâche (Enoka et Stuart, 1992). ...
... A la suite d'un marathon, Nicol et al. (1991cNicol et al. ( , 1991d) ont ainsi rapporté des baisses de 9 à 16 % en moyenne dans des test maximaux de type CED avec impact au sol (5 rebonds maximaux, drop-jump et sprint) voire aucune en CED sans impact (saut avec contre-mouvement) alors que les baisses de CMV et d'endurance isométrique des muscles extenseurs du genou étaient en moyenne de 26 et 39%, respectivement (Figure 34). Après un ultratrail, Koral et al. (2021) ont également rapporté une baisse de CMV deux à trois fois supérieure à la baisse de force lors d'un sprint sur cycloergomètre. Ainsi, l'évaluation des déficits neuromusculaires par des tâches isométriques n'est pas interchangeable avec l'évaluation par des tâches dynamiques (Krüger et al., 2019). ...
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Après une course d'endurance, le patron de récupération fonctionnelle est décrit comme biphasique, étant caractérisé par des déficits fonctionnels immédiats, suivis d'une récupération partielle à 2 h, avant de nouveaux déficits 1 à 2 jours plus tard ne s'atténuant que progressivement sur plusieurs jours. En raison du potentiel effet protecteur des hormones œstrogènes, notamment au niveau musculaire, les femmes pourraient mieux résister à la fatigue et récupérer plus rapidement. La littérature s’est néanmoins focalisée sur la récupération des hommes et principalement en phase aiguë. La phase retardée se caractérise pourtant par un phénomène inflammatoire lié à la régénérescence des microlésions musculaires causées par la course. Cette phase s’accompagne de courbatures musculaires qui disparaissent avant que la récupération ne soit complète, ce qui constitue un risque potentiellement accru de blessure à la reprise de la pratique. L’objectif principal de ce travail de thèse était d’établir et de comparer la cinétique de récupération structurale et fonctionnelle de coureurs féminins et masculins après une course d’endurance de 20 km avec dénivelé. Nos résultats soulignent l‘interaction entre le sexe et le test d’évaluation utilisé. Les femmes ont présenté plus de courbatures et d’altérations structurales (tant à l’échographie que par imagerie par résonnance magnétique) des muscles ischio-jambiers que les hommes. Par contre, leurs déficits fonctionnels étaient moindres et leur récupération plus précoce dans certains tests. Ce travail souligne la faiblesse des liens entre les altérations structurales et les déficits fonctionnels, autant que la richesse des ajustements neuromusculaires en situations dynamiques pluri-articulaires et musculaires. Les différences fonctionnelles observées entre les sexes semblent fortement influencées par l’organisation spécifique des synergies musculaires propres à chaque sexe.
... practical perspective, alternative testing procedures are recommended to assess fatigue-induced changes in runners. For example, the isometric force (maximal voluntary contractions of knee extensors and plantar flexors) deteriorates 2-3 times more than the F-V relationship parameters (maximal 7-s sprints on a cycle ergometer) after trail running races ranging from 40 to 170 km (Koral et al. 2021). ...
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This study aimed (i) to explore the reliability of the load–velocity relationship variables (load‐axis intercept [L0], velocity‐axis intercept [v0], and the area under the load–velocity relationship line [Aline]) obtained during the countermovement jump exercise in successive sessions and (ii) to examine the feasibility of the load–velocity relationship variables to detect acute changes in the lower‐body maximal mechanical capacities following different velocity‐based training (VBT) protocols. Twenty‐one recreational runners completed four randomized VBT protocols (three back squat sets with three minutes of rest) on separate occasions: (i) VBT with 60% of the one‐repetition maximum (1RM) and 10% velocity loss (VBT60–10); (ii) VBT with 60% 1RM and 30% velocity loss (VBT60–30); (iii) VBT with 80% 1RM and 10% velocity loss (VBT80–10); and (iv) VBT with 80% 1RM and 30% velocity loss (VBT80–30). The load–velocity relationship was determined before and after each VBT protocol using the two‐point method in the countermovement jump with a 0.5 kg load and another matching a mean velocity of 0.55 m·s⁻¹. All load–velocity relationship variables had an acceptable reliability (CV ≤ 5.61% and ICC ≥ 0.83, except for v0 between VBT60–30 and VBT80–10). Both v0 and Aline were reduced after VBT60–30 and VBT80–30 (p ≤ 0.044 and ES ≥ −0.47) but not after VBT60–10 and VBT80–10 (p ≥ 0.066 and ES ≤ −0.37). The post–pre differences were not significantly associated between VBT protocols for any load–velocity relationship variable (r ≤ 0.327 and p ≥ 0.148). Although the load–velocity relationship is reliable and sensitive to high‐repetition VBT protocols, its use to detect acute changes in the lower‐body maximal mechanical capacities is characterized by a high variability in individual responses.
... PFVP has been shown to be a reliable indicator of the maximal capacities of the neuromuscular system during multijoint tasks (31), making it an appropriate tool for evaluating the development of force, speed, and power in cycling exercises. Our study showed an increase in F 0 from Week 2 , whereas iMVC did not significantly change throughout the training protocol, indicating that both variables are not interchangeable, as previously reported (32,33). Additionally, a significant decrease in V 0 and a steeper S FV were observed at Week 7 compared with Pre, demonstrating that cycling-specific neuromuscular adaptations occur during SIT. ...
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Introduction: Previous studies ranging from 2 to 12 weeks of sprint interval training (SIT) have reported improvements in maximal oxygen uptake (V̇ O2max) and neuromuscular function in sedentary populations. However, whether the time course of the changes in these variables correlate with greater training volumes, is unclear. Methods: 13 sedentary participants performed three all-out training weekly sessions involving 15-s sprints interspersed with 2 minutes of recovery on a cycle-ergometer. The 6-week training program was composed of three identical blocks of 2-weeks in which training volume was increased from 10 to 14 repetitions over the first four sessions and reduced to 8 in the last session. The power output and the heart rate (HR) were monitored during the sessions. The V̇ O2max, the power-force-velocity profile (PFVP) and the isometric force were assessed every two weeks from baseline. Results: A significant increase in V̇ O2max was observed from the second week plateauing thereafter despite four additional weeks of training. The dynamic force production increased from the second week and the speed production decreased by the end of the protocol. The isometric force and the maximal power output from the PFVP did not change. Importantly, the time spent at high percentages of the maximal HR during the training sessions was lower in the second and third training block compared to the first. Conclusions: SIT resulted in a effective approach for rapidly increasing V̇ O2max and, no change in the isometric force was found, cycling-specific neuromuscular adaptations were observed from the second week of training. SIT may be useful in the short-term but further improvement of overall physical fitness might need other training modalities like endurance and/or resistance training.
... This is important as recent studies have shown that the magnitude of fatigue is affected by the characteristics of the task (i.e., dynamic vs. isometric measurements). This indicates that measurements in isometric and dynamic conditions might give different information about the individual's fatigue status (Koral et al. 2021). In this line, a 72 h recovery period was enough for both, young and older participants to restore their peak power output after a 3 × 20 s all-out session (Yasar et al. 2019). ...
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Background Recovery is a key factor to promote adaptations and enhance performance. Sprint Interval Training (SIT) is known to be an effective approach to improve overall physical function and health. Although a 2-day rest period is given between SIT sessions, the time-course of recovery after SIT is unknown. Purpose The aim of this study was to determine whether the neuromuscular and autonomic nervous systems would be impaired 24 and 48 h after an SIT session. Methods Twenty-five healthy subjects performed an 8 × 15 s all-out session on a braked cycle ergometer with 2 min of rest between repetitions. Isometric maximal voluntary contraction (iMVC) and evoked forces to electrical nerve stimulation during iMVC and at rest were used to assess muscle contractile properties and voluntary activation before (Pre), 1 (Post24h), and 2 (Post48h) days after the session. Two maximal 7 s sprints with two different loads were performed at those same time-points to evaluate the maximal theoretical force (F0), velocity (V0) and maximal power (Pmax) production during a dynamic exercise. Additionally, nocturnal heart rate variability (HRV) was assessed the previous and the three subsequent nights to the exercise bout. Results No significant impairments were observed for the iMVC or for the force evoked by electrical stimulation 1 day after the session. Similarly, F0, V0, and Pmax were unchanged at Post24h and Post48h. Furthermore, HRV did not reveal any temporal or frequential significant difference the nights following SIT compared to Pre. Conclusion The results of this study show a full recovery of neuromuscular and autonomic functions a day after an all-out SIT session.
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This study presents a novel method for evaluating the submaximal velocity-force (V(F)) relationship in mountain ultramarathon races using crowdsourced data from Strava.com. The dataset includes positional data from 408 participants of the 171-km UTMB® 2023 race (9,850-m D+). The race was divided into 100-m segments. The mean net propulsive force and velocity were computed for each segment to describe the submaximal V(F) relationship as a rational function of three parameters. F1: propulsive force at 1 m · s −1; V0: theoretical maximum velocity on flat terrain; C: curvature parameter (the lower C, the more linear the V(F) relationship). The V(F) profile parameters were found to be F1 = 1.80 ± 0.33 N · kg−1, V0 = 2.36 ± 0.42 m · s−1, and C = 0.66 ± 1.81, with good independence between the parameters within a group of homogeneous performance. The best athletes had the highest F1, V0, and C values. V(F) parameters were affected by fatigue during the race, with decreases of 20.9%, 32.0%, and 59.8% between the first and second parts of the race respectively. These findings suggest that the V(F) relationship is an interesting original approach for studying performance and fatigability during mountain ultra endurance races.
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Fatigue is a major symptom in many diseases, often among the most common and severe ones and may last for an extremely long period. Chronic fatigue impacts quality of life, reduces the capacity to perform activities of daily living, and has socioeconomical consequences such as impairing return to work. Despite the high prevalence and deleterious consequences of fatigue, little is known about its etiology. Numerous causes have been proposed to explain chronic fatigue. They encompass psychosocial and behavioral aspects (e.g., sleep disorders) and biological (e.g., inflammation), hematological (e.g., anemia) as well as physiological origins. Among the potential causes of chronic fatigue is the role of altered acute fatigue resistance, i.e. an increased fatigability for a given exercise, that is related to physical deconditioning. For instance, we and others have recently evidenced that relationships between chronic fatigue and increased objective fatigability, defined as an abnormal deterioration of functional capacity (maximal force or power), provided objective fatigability is appropriately measured. Indeed, in most studies in the field of chronic diseases, objective fatigability is measured during single-joint, isometric exercises. While those studies are valuable from a fundamental science point of view, they do not allow to test the patients in ecological situations when the purpose is to search for a link with chronic fatigue. As a complementary measure to the evaluation of neuromuscular function (i.e., fatigability), studying the dysfunction of the autonomic nervous system (ANS) is also of great interest in the context of fatigue. The challenge of evaluating objective fatigability and ANS dysfunction appropriately (i.e.,. how?) will be discussed in the first part of the present article. New tools recently developed to measure objective fatigability and muscle function will be presented. In the second part of the paper, we will discuss the interest of measuring objective fatigability and ANS (i.e. why?). Despite the beneficial effects of physical activity in attenuating chronic fatigue have been demonstrated, a better evaluation of fatigue etiology will allow to personalize the training intervention. We believe this is key in order to account for the complex, multifactorial nature of chronic fatigue.
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This study explored the effect of the menstrual cycle (MC) on the maximal neuromuscular capacities of the lower-body muscles obtained before and after a graded exercise test conducted on a treadmill to exhaustion. Sixteen physically active women were tested at -11 ± 3, -5 ± 3, and 5 ± 3 days from the luteinizing peak for the early follicular, late follicular, and mid-luteal phases. In each session, the individualized load-velocity (L-V) relationship variables (load-axis intercept [L0], velocity-axis intercept [v0], and area under the L-V relationship line [Aline]) were obtained before and after a graded exercise test conducted on a treadmill to exhaustion using the two-point method (three countermovement jumps with a 0.5 kg barbell and two back-squats against a load linked to a mean velocity of 0.55 m·s-1). At the beginning of each session, no significant differences were reported for L0 (P = 0.726; ES ≤ 0.18), v0 (P = 0.202; ES ≤ 0.37), and Aline (P = 0.429; ES ≤ 0.30) between phases. The MC phase × time interaction did not reach statistical significance for any L-V relationship variable (P ≥ 0.073). A significant main effect of “time” was observed for L0 (P < 0.001; ES = -0.77) and Aline (P = 0.002; ES = -0.59) but not for v0 (P = 0.487; ES = 0.12). These data suggest that the lower-body maximal neuromuscular capacities obtained before and after a graded treadmill test are not significantly affected by MC, although there is a high variability in the individual response.
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PurposeLower limbs’ neuromuscular force capabilities can only be determined during single sprints if the test provides a good fit of the data in the torque-velocity (T–V) and power-velocity (P–V) relationships. This study compared the goodness of fit of single sprints performed against traditional (7.5% of the body mass) vs. optimal load (calculated based on the force production capacity and ergometer specificities), and examined if reducing the load in fatigued state enhances T–V and P–V relationship goodness of fit.Methods Thirteen individuals performed sprints before (PRE) and after (POST) a fatiguing task against different loads: (1) TRAD: traditional, (2) OPT: optimal, and (3) LOW-OPT: optimal load reduced according to fatigue levels.ResultsAt PRE, OPT sprints presented a higher R2 of the T–V relationship (0.92 ± 0.06) and lower time to reach maximal power (Pmax) (48 ± 9%) when compared with TRAD sprints (0.89 ± 0.06 and 66 ± 22%, respectively, p < 0.01). At POST, the range of velocity spectrum was greater in the LOW-OPT (33 ± 4%) vs. TRAD (24 ± 3%) and OPT (26 ± 8%, p < 0.007). Similarly, the time to reach Pmax was lower in the LOW-OPT (46 ± 12%) vs. TRAD (76 ± 24%) and OPT (70 ± 24%, p < 0.006).Conclusion Sprints performed against an OPT load and reducing the OPT load after fatigue improve the fit of data in the T–V and P–V curves. Sprints load assignment should consider force production capacities rather than body mass.
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Purpose: Ultramarathon running includes two main types of events: single (SSR) and multi-stage races (MSR). Direct comparison of neuromuscular fatigue and recovery following SSR vs MSR race of comparable distance and elevation have never been performed. The aim of this study was to assess neuromuscular fatigue and recovery following two ultramarathons of equal distance performed either i) in a single stage or ii) in four successive days. Methods: Thirty-one runners participated in the study: 17 ran 169 km in a single stage race and 14 performed around 40 km/day over 4 days. The two races were performed on the same course. Neuromuscular function was tested before (PRE), after (POST), and 2 (D+2), 5 (D+5) and 10 (D+10) days after the races. Neuromuscular function was evaluated on both knee extensors (KE) and plantar flexors (PF) with voluntary and evoked contractions using electrical (femoral and tibial, respectively) nerve stimulation. Results: Reduction of voluntary activation measured in the KE was greater (i.e. central fatigue) for SSR than MSR directly after the race (-23% vs -7%), P<0.01). Reductions in evoked mechanical KE and PF responses on relaxed muscle (i.e. peripheral fatigue) of both KE and PF took longer to recover in MSR than in SSR. Conclusion: Performing prolonged running exercise over several days, each separated by rest, elicits more prolonged impairments in contractile function compared with single-stage ultra-marathon, while single-stage mountain ultra-marathon ran on the same course is associated with greater central fatigue.
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Background The force-velocity-power (FVP) profile is used to describe dynamic force production capacities, which is of great interest in training high performance athletes. However, FVP may serve a new additional tool for cardiac rehabilitation (CR) of coronary artery disease (CAD) patients. The aim of this study was to compare the FVP profile between two populations: CAD patients vs. healthy participants (HP). Methods Twenty-four CAD patients (55.8 ± 7.1 y) and 24 HP (52.4 ± 14.8 y) performed two sprints of 8 s on a Monark cycle ergometer with a resistance corresponding to 0.4 N/kg × body mass for men and 0.3 N/kg × body mass for women. The theoretical maximal force (F0) and velocity (V0), the slope of the force-velocity relationship (Sfv) and the maximal mechanical power output (Pmax) were determined. Results The Pmax (CAD: 6.86 ± 2.26 W.kg–1 vs. HP: 9.78 ± 4.08 W.kg–1, p = 0.003), V0 (CAD: 5.10 ± 0.82 m.s–1 vs. HP: 5.79 ± 0.97 m.s–1, p = 0.010), and F0 (CAD: 1.35 ± 0.38 N.kg–1 vs. HP: 1.65 ± 0.51 N.kg–1, p = 0.039) were significantly higher in HP than in CAD. No significant difference appeared in Sfv (CAD: −0.27 ± 0.07 N.kg–1.m.s–1 vs. HS: −0.28 ± 0.07 N.kg–1.m.s–1, p = 0.541). Conclusion The lower maximal power in CAD patients was related to both a lower V0 and F0. Physical inactivity, sedentary time and high cardiovascular disease (CVD) risk may explain this difference of force production at both high and low velocities between the two groups.
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Purpose: to evaluate the effects of a trail-running race on muscle oxidative function by measuring pulmonary gas exchange variables and muscle fractional O2 extraction. Methods: Eighteen athletes were evaluated before (PRE) and after (POST) a trail running competition of 32-km or 50-km with 2000 m or 3500 m of elevation gain, respectively. During the week before the race, runners performed an incremental uphill running test and an incremental exercise by utilizing a one-leg knee-extension (KE) ergometer. The KE exercise was repeated after the end of the race. During the KE test we measured oxygen uptake (V'O2) and micromolar changes in deoxygenated hemoglobin (Hb)+myoglobin (Mb) concentrations (Δ[deoxy(Hb+Mb)]) on vastus lateralis with a portable near-infrared spectroscopy. Results: V'O2peak was lower at POST vs. PRE (-23.9±9.0%, p<0.001). V'O2peak at POST was lower than V'O2 at the same workload at PRE (-8.4±15.6%, p<0.050). Peak power output and time to exhaustion decreased at POST by -23.7±14.3% and -18.3±11.3%, respectively (p<0.005). At POST the increase of Δ[deoxy(Hb + Mb)] as a function of work rate, from unloaded to peak, was less pronounced (from 20.2±10.1 to 64.5±21.1% of limb ischemia at PRE to 16.9±12.7 to 44.0±18.9% at POST). Peak Δ[deoxy(Hb+Mb)] values were lower at POST (by -31.2±20.5%; p<0.001). Conclusions: trail running leads to impairment in skeletal muscle oxidative metabolism, possibly related to muscle damage from repeated eccentric contractions. In association with other mechanisms, the impairment of skeletal muscle oxidative metabolism is likely responsible of the reduced exercise capacity and tolerance during and following these races.
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The aim of the present study was to examine the relationship of force-velocity (F-v) characteristics with age and race time in marathon runners. One hundred thirty five male marathon runners (age 44.2±8.8 years, height 176±6 cm, body mass 24.7±2.6 kg.m-2 and personal record 4:02±0:45 h:min), separated into eight age groups (<30, 30-35, ..., 55-60, >60 years), performed a F-v test on a cycle ergometer consisted of four 7s sprints. The older age groups had the lowest scores in maximal pedalling velocity (v0; p<0.001, ηp2=0.244), relative (rPmax; p=0.001, ηp2=0.176) and absolute maximal power (Pmax; p=0.009, ηp2=0.135), whereas no difference in maximal force (F0; p=0.558, ηp2=0.044) was shown. Race time correlated moderately with F0 (r=0.31, p<0.001) and Pmax (r=0.30, p=0.001). The small magnitude of age-related differences in anaerobic power among most age groups indicated that humans without muscle strength/power training might maintain anaerobic power indices till their 60’s. Keywords: aging, anthropometry, cycle ergometer, muscle strength, speed
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While fatigue can be defined as an exercise-related decrease in the maximal power or isometric force, most studies have assessed only isometric force. The main purpose of this experiment was to compare dynamic measures of fatigue [maximal torque (Tmax), maximal velocity (Vmax) and maximal power (Pmax)] with measures associated with maximal isometric force [isometric maximal voluntary contraction (IMVC) and maximal rate of force development (MRFD)] 10 s after different fatiguing exercises and during the recovery period (1-8 min after). Ten young men completed 6 experimental sessions (3 fatiguing exercises×2 types of fatigue measurements). The fatiguing exercises were: a 30-s all out (WING), 10-min at severe-intensity (SEV) and 90-min at moderate-intensity (MOD). Relative Pmax decreased more than IMVC after WING (p=0.005) while the opposite was found after SEV (p=0.005) and MOD tasks (p<0.001). There was no difference between the decrease in IMVC and Tmax after the WING, but IMVC decreased more than Tmax immediately following and during the recovery from the SEV (p=0.042) and MOD exercises (p<0.001). Depression of MRFD was greater than Vmax after all the fatiguing exercises and during recovery (all p<0.05). Despite the general definition of fatigue, isometric assessment of fatigue is not interchangeable with dynamic assessment following dynamic exercises with large muscle mass of different intensities, i.e. the results from isometric function cannot be used to estimate dynamic function and vice-versa. This implies different physiological mechanisms for the various measures of fatigue.
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Purpose: The assessment of power changes after fatiguing exercise provides important additional information about neuromuscular function compared to traditional isometric measurements, especially when exploring age-related changes in fatigability. Therefore, the aim of this review was to explore the effects of age on neuromuscular fatigue (NMF) when measured in isometric compared with dynamic contractions. The importance of central and peripheral mechanisms contributing to age-related NMF were discussed. Methods: Medline, EMBASE, Cochrane Central Register of Controlled Trials, and SPORT Discus databases were searched. The combination of terms related to the intervention (fatiguing exercise), population (old people) and outcomes (isometric force and power) were used. This meta-analysis was registered on PROSPERO (CRD42016048389). Results: Thirty-one studies were included. The meta-analyses revealed that force decrease was greater (there was more NMF) in young subjects than their older counterparts when fatigue was induced by isometric tasks (ES = 0.913, CI = 0.435 to 1.391, P < 0.001), but not when the fatiguing exercise was performed in dynamic mode (ES = 0.322, CI: -0.039 to 0.682, P = 0.08). Older individuals demonstrated a greater reduction in power after fatigue induced by either dynamic or isometric tasks (ES = -0.891, CI: -1.657 to -0.125, P = 0.023). Conclusion: There is no difference in the isometric force loss between young and old people when fatigue is induced by dynamic tasks. However, maximal power is more decreased following fatigue tasks in older adults. Thus, the assessment of fatigue (isometric force vs. power) must be considered in identifying age-related NMF mechanisms.
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Purpose: This study explored the feasibility of the force-velocity relationship (F-V) to detect the acute effects of different fatigue protocols on the selective changes of the maximal capacities of upper body muscles to produce force, velocity, and power. Methods: After determining the bench press one-repetition maximum (1RM), participants' F-V relationships were assessed during the bench press throw exercise on five separate sessions after performing one of the following fatiguing protocols: 60%1RM failure, 60%1RM non-failure, 80%1RM failure, 80%1RM non-failure, and no-fatigue. In the non-failure protocols, participants performed half the maximum number of repetitions than in their respective failure protocols. Results: The main findings revealed that (1) all F-V relationships were highly linear (median r = 0.997 and r = 0.982 for averaged across participants and individual data, respectively), (2) the fatiguing protocols were ranked based on the magnitude of power loss as follows: 60%1RM failure > 80%1RM failure > 60%1RM non-failure > 80%1RM non-failure, while (3) the assessed maximum force and velocity outputs showed a particularly prominent reduction in the protocols based on the lowest and highest levels of fatigue (i.e., 80%1RM non-failure and 60%1RM failure), respectively. Conclusions: The results support the use of F-V to assess the effects of fatigue on the distinctive capacities of the muscles to produce force, velocity, and power output while performing multi-joint tasks, while the assessed maximum force and velocity capacities showed a particularly prominent reduction in the protocols based on the lowest and highest levels of fatigue (i.e., 80%1RM non-failure and 60%1RM failure), respectively.
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This study aimed to compare the effect of three interset rest intervals (1, 3, and 5 minutes) on (I) mean velocity during a resistance training session conducted in a Smith machine with the squat and bench press exercises, and (II) the pre- and post-exercise force-velocity relationship. Fifteen male university students completed three sessions (i.e., Rest 1ʹ, Rest 3ʹ, and Rest 5ʹ) consisting of three sets of five repetitions against the 10RM load during the squat and bench press exercises. The force-velocity relationship (maximal values of force [F 0], velocity [v0], and power [Pmax]) was evaluated at the beginning and at the end of each session with the countermovement jump and bench press throw exercises. During training, mean velocity was slower in sets 2 and 3 of the Rest 1ʹ protocol compared to Rest 3ʹ and Rest 5ʹ, but no significant differences were present between Rest 3ʹ and Rest 5ʹ. After training, there was a significant decrease in F 0 (p = 0.017) and Pmax (p = 0.010), but not in v0 (p = 0.259). These results support the Rest 3ʹ as the most time-efficient protocol, among those analysed, for the maintenance of high mean velocities during training sessions not leading to failure.
Article
Abstract. Purpose: The aim of the present study was to examine the effect of age on the relationship between jumping and cycling tests of short-term power in team handball (TH) players. Methods: A cross-sectional study was conducted, in which adolescent and adult TH players (n = 96, age 19.6±6.9 yrs, body mass 75.8±14.1 kg, height 1.78±0.10, mean±standard deviation) performed four jumping tests (i.e., squat jump, countermovement jump, Abalakov jump and a 30-s Bosco test), and two tests on cycle ergometer (i.e. force-velocity (F-v) test and Wingate anaerobic test (WAnT)). Heart rate (HR) was monitored during Bosco test and WAnT. Participants were classified into four age groups (12.1–15.0 yrs, U15; 15.1–18.0 yrs, U18; 18.1–25.0 yrs, U25; and 25.1–35.0 yrs, O25). Results: Differences of moderate to large magnitude among groups were observed with regards to all variables of the F-v test, WAnT and jumping tests, in which the older groups had higher scores in all variables than their younger counterparts (p < 0.05). Correlation between mean power in WAnT (8.0±1.0 W.kg−1) and Bosco test (29.3±7.1 W.kg−1) was r = 0.70 (p < 0.001) in the total sample (ranging from r = 0.43, p = 0.075 in O25 to r = 0.72 in U15, p < 0.001). Correlation between HR in WAnT (179±12 bpm) and Bosco test (162±14 bpm) was r = 0.75 (p < 0.001) in the total sample (ranging from r = 0.65, p < 0.001 in U18 to r = 0.81 in O25, p < 0.001). Conclusions: These findings might help TH coaches and fitness trainers to monitor short-term power of their athletes and to use properly cycling and jumping tests. Key words: Growth, development, sport, physical fitness, age groups