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This study explores the cardiorespiratory and muscular fatigue responses to downhill (DR) vs uphill running (UR) at similar running speed or similar oxygen uptake (V̇O2). Eight well-trained, male, trail runners completed a maximal level incremental test and three 15-min treadmill running trials at ±15% slope: i) DR at ~6 km·h−1 and ~19% V̇O2max (LDR); ii) UR at ~6 km·h−1 and ~70% V̇O2max (HUR); iii) DR at 19 km·h−1 and ~70% V̇O2max (HDR). Cardiorespiratory responses and spatiotemporal gait parameters were measured continuously. Maximal isometric torque was assessed before and after each trial for hip and knee extensors and plantar flexor muscles. At similar speed (~6 km·h−1), cardiorespiratory responses were attenuated in LDR vs HUR with altered running kinematics (all p < 0.05). At similar V̇O2 (~3 l·min−1), heart rate, pulmonary ventilation and breathing frequency were exacerbated in HDR vs HUR (p < 0.01), with reduced torque in knee (−15%) and hip (−11%) extensors and altered spatiotemporal gait parameters (all p < 0.01). Despite submaximal metabolic intensity (70% V̇O2max), heart rate and respiratory frequency reached maximal values in HDR. These results further our understanding of the particular cardiorespiratory and muscular fatigue responses to DR and provide the bases for future DR training programs for trail runners.
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Journal of Sports Sciences
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High-intensity downhill running exacerbates heart
rate and muscular fatigue in trail runners
Marcel Lemire , Romain Remetter , Thomas J. Hureau , Blah Y. L. Kouassi ,
Evelyne Lonsdorfer , Bernard Geny , Marie-Eve Isner-Horobeti , Fabrice
Favret & Stéphane P. Dufour
To cite this article: Marcel Lemire , Romain Remetter , Thomas J. Hureau , Blah Y. L. Kouassi ,
Evelyne Lonsdorfer , Bernard Geny , Marie-Eve Isner-Horobeti , Fabrice Favret & Stéphane P.
Dufour (2020): High-intensity downhill running exacerbates heart rate and muscular fatigue in trail
runners, Journal of Sports Sciences
To link to this article: https://doi.org/10.1080/02640414.2020.1847502
Published online: 15 Nov 2020.
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SPORTS PERFORMANCE
High-intensity downhill running exacerbates heart rate and muscular fatigue in trail
runners
Marcel Lemire
a,b
, Romain Remetter
a,c
, Thomas J. Hureau
a,b
, Blah Y. L. Kouassi
a,b
, Evelyne Lonsdorfer
a,c
, Bernard Geny
a,c
,
Marie-Eve Isner-Horobeti
a,d
, Fabrice Favret
a,b
and Stéphane P. Dufour
a,b
a
Faculty of Medicine, University of Strasbourg, Translational Medicine Federation (FMTS), Strasbourg, France;
b
Faculty of Sport Sciences, University of
Strasbourg, Strasbourg, France;
c
Physiology and Functional Explorations Department, University Hospitals of Strasbourg, Civil Hospital, Strasbourg,
France;
d
Physical and Rehabilitation Medicine Department, University of Strasbourg, University Institute of Rehabilitation Clémenceau, Strasbourg,
France
ABSTRACT
This study explores the cardiorespiratory and muscular fatigue responses to downhill (DR) vs uphill
running (UR) at similar running speed or similar oxygen uptake (V
̇O
2
). Eight well-trained, male, trail
runners completed a maximal level incremental test and three 15-min treadmill running trials at ±15%
slope: i) DR at ~6 km·h
−1
and ~19% V
̇O
2max
(LDR); ii) UR at ~6 km·h
−1
and ~70% V
̇O
2max
(HUR); iii) DR at
~19 km·h
−1
and ~70% V
̇O
2max
(HDR). Cardiorespiratory responses and spatiotemporal gait parameters
were measured continuously. Maximal isometric torque was assessed before and after each trial for hip
and knee extensors and plantar exor muscles. At similar speed (~6 km·h
−1
), cardiorespiratory responses
were attenuated in LDR vs HUR with altered running kinematics (all p < 0.05). At similar V
̇O
2
(~3 l·min
−1
),
heart rate, pulmonary ventilation and breathing frequency were exacerbated in HDR vs HUR (p < 0.01),
with reduced torque in knee (−15%) and hip (−11%) extensors and altered spatiotemporal gait para-
meters (all p < 0.01). Despite submaximal metabolic intensity (70% V
̇O
2max
), heart rate and respiratory
frequency reached maximal values in HDR. These results further our understanding of the particular
cardiorespiratory and muscular fatigue responses to DR and provide the bases for future DR training
programs for trail runners.
ARTICLE HISTORY
Accepted 4 November 2020
KEYWORDS
Oxygen uptake; heart rate;
muscle torque; running
kinematics; inclined
treadmill
Introduction
Paragraph 1. Trail running has become very popular over the
last 20 years. These outdoor mountain running races extend
from short trails to extreme events (i.e., ultra-long distances
and/or large cumulative ascent-descent) but systematically
involve uphill (UR) as well as downhill running (DR) sections.
Physiological studies have highlighted the marked dierences
in DR vs UR with direct consequences in pacing as well as in
training strategies (Born et al., 2016). Most of the dierences
between DR and UR are considered to be related to the type of
muscle actions on which they rely (Vernillo et al., 2016). For
instance, DR is known to require preferentially eccentric muscle
actions (i.e., lengthening muscle actions) to generate the neces-
sary braking component within the major extensor muscles of
the lower limbs whereas UR predominantly relies on concentric
muscle actions (i.e., shortening muscle actions) to move the
runner’s body up despite gravity (Lindstedt et al., 2001).
Paragraph 2. Downhill running is characterized by the high
running speeds that can be achieved despite very low energy
requirements. Conversely, UR features much lower running
velocities but considerably greater energy cost (Minetti et al.,
2002). When both running modes are compared at similar
slopes and running speeds (thereby limiting the comparison
to very low running speed in UR) (Lemire et al., 2018) or similar
heart rate (HR) (Garnier et al., 2019), oxygen uptake (V
̇O
2
) and
ventilation (V
̇
E
) are lower in DR. However, when DR and UR are
compared at the same slope and similar V
̇O
2
, running speed is
much greater in DR, together with higher HR (Kolkhorst et al.,
1996; Lemire et al., 2020b). Previous studies in this area have
used either short stages during incremental tests (i.e., 2 min
stages) (Breiner et al., 2018; Kolkhorst et al., 1996; Lemire et al.,
2020b) and/or were limited to low exercise intensities (i.e., V
̇O
2
levels < 40 ml∙kg
−1
∙min
−1
) (Kolkhorst et al., 1996; Pokora et al.,
2014). Moreover, the ability to maintain a stable V
̇O
2
and there-
fore the tolerance to high-intensity DR at steep slopes (i.e.,
>10%) has not been specically addressed. Indeed, UR at 10%
slope has been shown to increase the amplitude of the V
̇O
2
slow component compared to level running (Pringle et al.,
2002). Although an upward drift in V
̇O
2
has been described
during low intensity (i.e., <50% V
̇O
2max
) prolonged DR (Dick &
Cavanagh, 1987; Westerlind et al., 1994), the behaviour of V
̇O
2
and other cardiorespiratory parameters during high-intensity
constant speed DR at steep slope remains unexplored, albeit
this knowledge would help prescribing specic training ses-
sions and designing training programs for trail runners.
Paragraph 3. Despite the low energy cost of DR, some
recent studies have shown that trail races can induce marked
muscular fatigue with up to 40% loss of lower limb extensors
muscle strength (hip, knee and ankle) (Baiget et al., 2016;
Easthope et al., 2010). This fatigue is considered to be mainly
related to a combination of local muscle metabolic perturba-
tions potentially altering muscle contractile processes and/or
CONTACT Marcel Lemire marcel.lemire@unistra.fr Faculty of Sport Sciences, University of Strasbourg, Strasbourg 67084, France
JOURNAL OF SPORTS SCIENCES
https://doi.org/10.1080/02640414.2020.1847502
© 2020 Informa UK Limited, trading as Taylor & Francis Group
mechanical loading on the muscle-tendon complex in the
lower limbs, possibly leading to profound skeletal muscle
damage (Giandolini et al., 2016b). In this context, signicant
reductions in knee extensor torque have been observed after
both pure UR and DR (Giandolini et al., 2016b; Lazzer et al.,
2015), but the respective contribution of the mechanical and
metabolic loads to the muscular fatigue observed after DR vs
UR remains unclear.
Paragraph 4. Therefore, the main purpose of this study
was to determine the cardiorespiratory responses of well-
trained trail runners to DR vs UR at steep slopes performed
at similar running speed and at similar oxygen uptake (i.e.,
high intensity running exercise). A secondary purpose of
this study was to explore the exercise-induced torque loss
observed after high-intensity DR vs UR performed at steep
slopes.
Materials and methods
Participants and ethical approval
Paragraph 5. Eight well-trained male trail runners partici-
pated in this study (age: 29 ± 10 [mean ± SD] years; height:
1.74 ± 0.03 m; body mass: 61.8 ± 5.0 kg; BMI:
20.4 ± 2.0 kg·m2; maximal oxygen uptake (V
̇O
2max
):
68.0 ± 6.4 ml·min
−1
·kg
−1
; maximal HR: 183 ± 8 bpm;
12 ± 4 years training history and 2503 ± 1092 km·year
−1
of training). The number of subjects included in this study
has been calculated to detect a 10% torque loss in DR
(Giandolini et al., 2016a). Therefore, a statistical power of
0.9 and an alpha risk of 0.05 required 8 subjects to be
included. All athletes were informed of the benets and
risks of this investigation prior to giving their written
informed consent to participate in the study. They were
also instructed not to consume alcohol or caeine in the
3 h before each test and to refrain from strenuous and
exhaustive exercise 24 h prior to each test. All were healthy,
without current injuries and did not take any medication.
The experiment was previously approved by our
Institutional Review Board and complied with the
Declaration of Helsinki (CPP18-039a/2108-A00700-55).
Experimental design
Paragraph 6. In eight separate sessions (Figure 1), each athlete
performed each of the following experimental test: i) a maximal
level running incremental test on a treadmill to determine level
running V
̇O
2max
; ii) four DR familiarization sessions; iii) three
constant speed inclined (+ or 15% slope) running trials (one
UR and two DR). All constant speed trials were randomized,
except high-intensity UR which had to be performed before
low-intensity DR at the same running speed. All trials were
performed at the same time of the day and were separated
by at least 4 days.
Familiarization sessions to downhill running
Paragraph 7. To minimize muscle damage, the subjects were
familiarized with DR using 4 separate familiarization trials with
a constant negative slope of −15%: 1) 5-min DR at 60–70% level
running speed at V
̇O
2max
(vV
̇O
2max
), 2) 10 min DR at 60–90% v_
V
O
2max
(4 min at 60% vV
̇O
2max
, then 2 min stages with 10%
vV
̇O
2max
increment), 3) 16 min DR (5 min DR at 60%, 5 min at
80%, 3 times 1 min at 100% vV
̇O
2max
and 1 min DR recovery at
60% vV
̇O
2max
between each bout), 4) the same workout than
the third familiarization session except that the intensity of
3 × 1 min trials was set at 120% vV
̇O
2max
.
Incremental and constant speed running tests
Paragraph 8. All athletes performed an incremental test until
exhaustion on a level treadmill (Pulsar, H/P Cosmos, Nussdorf-
Traunstein, Germany). The participants began the rst stage at
13 km·h
−1
during 2 min and the running speed was increased
by 1 km·h
−1
every 2 min until volitional exhaustion.
Paragraph 9. Three constant speed running trials of
15 min duration were also performed by all athletes: i)
one DR bout at 70% V
̇O
2max
(−15% slope, HDR), ii) one UR
bout at 70% V
̇O
2max
(+15% slope, HUR) and iii) one DR bout
at similar treadmill speed to the UR trial (−15% slope, LDR).
Previous data from the same subjects collected during DR
(−15%) and UR (+15%) maximal incremental tests (Lemire
et al., 2020b) were used to establish the running speed
Figure 1. Protocol design.
2M. LEMIRE ET AL.
allowing to reach 70% V
̇O
2max
during HUR and HDR trials.
Pilot testing also demonstrated that 70% V
̇O
2max
was the
highest exercise intensity that our athletes were able to
maintain for 15 minutes during DR at −15% slope.
Gas exchange measurements
Paragraph 10. During all running trials, V
̇O
2
, carbon dioxide
output (V
̇CO
2
), V
̇
E
, respiratory frequency, tidal volume (V
T
) and
respiratory exchange ratio (RER) were collected breath-by-
breath though a facemask with an open-circuit metabolic cart
with rapid O
2
and CO
2
analysers (Metamax Cortex, Leipzig,
Germany). Before each exercise test, the pneumotachograph
was calibrated according to manufacturer’s instructions. Heart
rate was continuously measured (Polar S810, Polar, Kempele,
Finland). Maximal oxygen consumption was dened as the
highest 30 s V
̇O
2
value. The level running speed associated with
V
̇O
2max
(vV
̇O
2max
) was determined where V
̇O
2
reaches a plateau
or if the increase in V
̇O
2
was less than 2.1 ml·kg
−1
·min
−1
for
a speed increase equal to 1 km·h
−1
(Billat & Koralsztein, 1996).
During the constant speed trials, slow components in the car-
diorespiratory responses were established using the dierence
between end-exercise and 3
rd
minute values (Poole & Jones,
2012).
Blood lactate analyses
Paragraph 11. Blood lactate concentration (b[La]) was
assessed from earlobe blood samples (200 µl of blood) before
and after 1 and 3 min of recovery after each running test
(Lactate Scout+, EKF Diagnostics, Leipzig, Germany).
Isometric maximal torque assessment
Paragraph 12. Before and within the rst 2 min after each
constant speed running trial, hip extensor, knee extensor and
plantar exor strengths were assessed using a handheld
dynamometer (microFET®2; Hoggan Scientic, Salt Lake City,
UT, USA) during isometric maximal voluntary contraction. The
coecient of variation for force measurement using this device
has previously been demonstrated to be 3.2–4.2%, with limits
of agreement of 13.8–19.2% (Mentiplay et al., 2015; Mu et al.,
2016). All tests were performed with the right lower limb for
each athlete (dominant limb), in duplicates with 1-min rest
between attempts in the following order: plantar exor, knee
extensor and hip extensor. The same experimenter conducted
all the measures and was standing systematically with his back
or his elbow against the wall to secure a solid position during all
maximal voluntary contractions (Figure 2). These measure-
ments were initially collected in Newton and subsequently
converted in torque using anatomic measures of hip and
knee extensors and plantar exor lever arms. The best value
was kept for analyses.
Hip Extensors. In order to assess isometric maximal volun-
tary contraction in hip extensors the participant was asked to
place his hip exed at 90° in dorsal decubitus position on the
examination table (Figure 2(c)). The dynamometer was placed
on the posterior side of the thigh, proximal to the knee joint
and the participant was asked to perform a maximal isometric
hip extension contraction for 5 s.
Knee Extensors. The athlete sat comfortably on the edge of
the examination table with a high-density corner cushion
Figure 2. Schematic representation of isometric maximal voluntary contraction measurement for knee extension, plantar flexion, and hip extension (Panel a, b and
c respectively).
JOURNAL OF SPORTS SCIENCES 3
under the knees, with hips and knees exed at 90° (Figure 2(a)).
The dynamometer was placed on the anterior aspect of the
shank, just above the ankle joint and the participant was asked
to perform a maximal isometric knee extension contraction for
5 s.
Plantar Flexors. The participant was lying supine with ankle
at 0°and hips and knees at 180°. The dynamometer was placed
under the metatarsal heads (Figure 2(b)). The participant was
then asked to perform a maximal isometric plantar exion
contraction for 5 s.
Spatiotemporal parameters
Paragraph 13. Spatiotemporal parameters were measured
using the OptoGait system (OptoGait; Microgate, Bolzano,
Italy) (Healy et al., 2019). The device used two parallel bars,
covering the length of the treadmill belt, that were placed on
the side edges of the treadmill as near as possible to the
contact surface. Before each test, the device was systemically
calibrated for each subject and the shoes length was measured
as a number of LEDs by maintaining a foot on the treadmill
between the bars. Contact time, step length and step frequency
were measured over 30 s at the 3
rd
and the 15
th
min for the
constant running speed trials.
Statistical analyses
Paragraph 14. Statistical analyses were performed using
Statistica (13.5, Tulsa, Oklahoma, USA). All data are expressed
as mean ± standard derivation (SD). After testing for data
distribution normality with Kolmogorov–Smirnov test and
equal variances with Bartlett test, two-way analysis of variance
(ANOVAs) on repeated measures were performed to assess the
eect of exercise time (baseline, 3 min and 15 min) and exercise
modes (HDR, HUR, LDR) on the cardiorespiratory responses and
the spatiotemporal parameters. One-way ANOVAs on repeated
measures were performed to assess the eect of exercise mode
on linear regression slope and y-intercept of the relationship
between HR and V
̇O
2
. Three-way ANOVAs on repeated mea-
sures were also performed to assess the eect of exercise time,
exercise mode and joint on lower limb torque (ankle, knee and
hip extensors). When signicant interactions were observed,
Tukey’s honestly signicant dierence post-hoc tests were
used to localize the signicant dierences. For all statistical
analyses, p ≤ 0.05 was considered statistically signicant.
Results
All cardiorespiratory parameters are presented in Table 1 and
no dierence occurred at rest among conditions (p > 0.05)
(Table 1).
Comparing downhill and uphill running at similar running
speed
Paragraph 15. At similar running and vertical velocities, V
̇O
2
and V
̇CO
2
were ~3 fold higher (p < 0.001) despite similar RER in
HUR vs LDR at the 3
rd
and 15
th
min of exercise (Figure 3(a) and
Table 1). Blood lactate was not signicantly dierent between
conditions at 1- and 3-min after end-exercise (p = 0.807 and
p = 0.381, respectively).
Pulmonary ventilation was also ~1.8 and 2.4-fold higher in
HUR than in LDR after 3 and 15 min, respectively (both
p < 0.001). The greater V
̇
E
response in HUR vs LDR was asso-
ciated with a higher tidal volume (all p < 0.001) despite similar
respiratory frequency at the 3
rd
min of exercise (p = 0.487;
Figure 4(a-c)) whereas both tidal volume and respiratory fre-
quency were greater in HUR vs LDR after 15 min exercise
(p < 0.001 and p = 0.005, respectively). Despite similar running
velocities, HR was higher in HUR vs LDR at both the 3
rd
and 15
th
min time points (Figure 3(b), p < 0.001).
All cardiorespiratory parameters achieved a steady state
with no further changes between the 3
rd
and 15
th
min during
LDR and HUR (p = 0.734–1.000), except for HR which signi-
cantly increased during HUR only (p = 0.007).
No dierence was observed in hip extensor, knee extensor and
plantar exor isometric torque before HUR and LDR (Figure 5), and
these values remained unchanged post-exercise (both p = 1.000).
While stride frequency was ~8% higher in HUR than in LDR
at the 3
rd
min and ~11% higher at the 15
th
min (all p < 0.001),
stride length was ~9% longer and contact time was ~40%
greater in LDR than in HUR at both the 3
rd
and 15
th
min time
Table 1. Metabolic and cardiorespiratory responses to downhill vs uphill running at similar speed or oxygen uptake.
Time Rest 3 min 15 min
Condition HDR HUR LDR HDR HUR LDR HDR HUR LDR
Treadmill speed (km·h
−1
) - - - 18.9 ± 2.0† 6.2 ± 0.7 6.2 ± 0.7 18.9 ± 2.0† 6.2 ± 0.7 6.2 ± 0.7
Vertical speed (m·s
−1
) - - - −0.78 ± 0.08† 0.26 ± 0.03 −0.26 ± 0.03† −0.78 ± 0.08† 0.26 ± 0.03 −0.26 ± 0.03†
V
O
2
(l·min
−1
) 0.311 ± 0.139 0.315 ± 0.137 0.318 ± 0.107 2.575 ± 0.282†‡ 2.876 ± 0.199‡ 0.804 ± 0.217†‡ 2.946 ± 0.379§ 2.949 ± 0.225 0.796 ± 0.208†
V
O
2
(ml·kg
−1
·min
−1
) 7.3 ± 2.1 6.7 ± 1.8 5.5 ± 1.6 41.8 ± 4.7†‡ 46.5 ± 3.5‡ 13.0 ± 3.3†‡ 47.7 ± 6.4§ 47.9 ± 3.3 12.8 ± 3.2†
b[La] (mmol·l
−1
) R1 1.2 ± 0.4 1.1 ± 0.5 1.3 ± 0.5 - - - 2.9 ± 1.1‡ 1.8 ± 0.4 1.2 ± 0.4
b[La] (mmol·l
−1
) R3 3.3 ± 1.9†‡ 1.8 ± 0.7 0.9 ± 0.4
RER 0.78 ± 0.06 0.76 ± 0.06 0.78 ± 0.7 0.83 ± 0.04‡ 0.84 ± 0.04‡ 0.90 ± 0.06‡ 0.90 ± 0.09 0.86 ± 0.06 0.80 ± 0.06§
V
E
(l·min
−1
) 9.8 ± 3.5 10.0 ± 4.9 10.1 ± 3.0 72.7 ± 9.6‡ 66.3 ± 8.1‡ 24.0 ± 5.5†‡ 96.7 ± 17.4§ 70.4 ± 7.7 21.2 ± 5.0†
RF (breaths·min
−1
) 17.5 ± 4.6 16.1 ± 4.3 16.9 ± 3.4 47.3 ± 7.2†‡ 32.5 ± 5.3‡ 28.1 ± 4.8‡ 56.1 ± 9.3§ 35.8 ± 5.9 26.9 ± 3.7†
V
T
(l) 0.59 ± 0.24 0.63 ± 0.20 0.61 ± 0.24 1.61 ± 0.32†‡ 2.06 ± 0.26‡ 0.88 ± 0.26†‡ 1.73 ± 0.39 2.03 ± 0.40 0.81 ± 0.36†
t
I
(s) 1.26 ± 0.34 1.24 ± 0.26 1.27 ± 0.32 0.67 ± 0.13†‡ 0.92 ± 0.18‡ 0.96 ± 0.26‡ 0.53 ± 0.20† 0.85 ± 0.24 0.98 ± 0.25
t
E
(s) 1.95 ± 0.49 2.10 ± 0.59 2.06 ± 0.41 0.67 ± 0.12‡ 0.98 ± 0.14‡ 1.15 ± 0.24‡ 0.56 ± 0.28 0.90 ± 0.27 1.19 ± 0.45
t
I
/t
TOT
0.39 ± 0.06 0.38 ± 0.05 0.39 ± 0.04 0.50 ± 0.04‡ 0.48 ± 0.02‡ 0.46 ± 0.05‡ 0.49 ± 0.04 0.48 ± 0.03 0.45 ± 0.05
HR (bpm) 66 ± 17 58 ± 13 62 ± 15 157 ± 10†‡ 141 ± 9‡ 92 ± 12†‡ 179 ± 13†§ 151 ± 12§ 93 ± 12†
Note. Values are means ± SD of 8 athletes in all conditions. HDR: downhill running at 70% V
̇O
2max
, HUR: uphill running at 70% V
̇O
2max
and LDR: downhill running at
similar running speed than HUR. † p < 0.05 vs HUR at the same time point, ‡ p < 0.05 vs rest in the same condition and § p < 0.05 vs 3 min in the same condition;
oxygen uptake (V
̇O
2
), blood lactate (b[La]) 1- (R1) and 3-min (R3) after end-exercise, respiratory exchange ratio (RER), minute pulmonary ventilation (V
̇
E
), respiratory
frequency (RF), tidal volume (V
T
), inspiration time (t
I
), expiration time (t
E
), duty cycle (t
I
/t
TOT
), heart rate (HR).
4M. LEMIRE ET AL.
points (Figure 6; all p < 0.001). No change was noted in any of
these parameters between the 3
rd
and 15
th
min of exercise.
Comparing downhill and uphill running at similar oxygen
uptake
Paragraph 16. Despite ~2-fold greater treadmill and vertical
running velocities in HDR vs HUR (Table 1), V
̇O
2
and V
̇CO
2
were
~10% lower in HDR vs HUR after 3 min of exercise (p < 0.004).
This dierence did not persist further (Figure 3(a)), such that
similar V
̇O
2
, V
̇CO
2
and RER were observed between trials at the
15
th
min (p = 1.000, 0.766 and 0.668, respectively), due the
progressive emergence of signicant V
̇O
2
and V
̇CO
2
slow com-
ponents during HDR (p < 0.001). Similar V
̇O
2
and V
̇CO
2
were also
observed when averaged between the 3
rd
and 15
th
min in each
trial (V
̇O
2
:2.828 ± 0.285 l·min
−1
in HDR vs 2.934 ± 0.218 l·min
−1
in
HUR, p = 0.163; V
̇CO
2
: 2.495 ± 0.246 l·min
−1
in HDR vs
2.518 ± 0.192 l·min
−1
in HUR, p = 0.800). At end exercise, b[La]
was similar after 1 min recovery (p = 0.131), but higher after
3 min recovery in HDR vs HUR (p = 0.017).
Heart rate was greater in HDR vs HUR at both the 3
rd
and
15
th
min time points (Table 1). Pulmonary ventilation was simi-
lar between trials after 3 min of exercise but became increas-
ingly greater thereafter in HDR vs HUR, describing a V
̇
E
slow
component (p < 0.001, Figure 4(a)). The larger V
̇
E
response
observed in HDR was accompanied by lower tidal volume but
higher respiratory frequency (p = 0.003 and p < 0.001, respec-
tively, Table 1).
The HR/V
̇O
2
and V
̇
E
/V
̇O
2
relationships were dierent
between HDR and HUR either because of greater y-intercept
(HR/V
̇O
2
, p = 0.002, Figure 7(a)) or greater slope (V
̇
E
/V
̇O
2
,
p = 0.030, Figure 7(b)). Conversely, the V
̇CO
2
/V
̇O
2
relationships
were similar in HDR and HUR (Figure 7(c)).
Of note, the respiratory frequency and HR achieved at the
15
th
min during HDR were similar to the maximal values mea-
sured during the level running incremental test (58
breaths
−1
·min
−1
and 183 bpm, respectively, p = 0.579 and
p = 0.240, respectively).
No dierence was observed in hip extensor, knee extensor
and plantar exor isometric torque before HUR and HDR (Figure
5). However, HDR induced substantial torque losses in hip
extensor (−11%) and knee extensor (−15%) whereas plantar
exor torque loss did not reach signicance (p = 0.353).
Similar percentage change and signicance level were
obtained regarding torque normalized to body mass
(2.30 ± 0.64 to 2.03 ± 0.57 Nm·kg
−1
for hip extension,
3.07 ± 1.04 to 2.66 ± 0.98 Nm·kg
−1
for knee extension and
1.67 ± 0.59 to 1.52 ± 0.65 Nm·kg
−1
for plantar exion).
Greater stride frequency (+24%) and longer stride length
(+141%) together with much shorter contact time (−60%) were
Figure 3. Time course of the oxygen consumption (panel a) and heart rate (panel b) responses during the 15 min trials. Black symbols: DR at 70% V
̇O
2max
(HDR); white
symbols: UR at 70% V
̇O
2max
(HUR); grey symbols: DR at the same running speed than UR (LDR). Horizontal dashed lines indicate maximal values measured during the
level running incremental test. Values are means ± SD of 8 athletes.
JOURNAL OF SPORTS SCIENCES 5
observed in HDR vs HUR at both the 3
rd
and 15
th
min time points
(Figure 6; all p < 0.001). None of these parameters displayed
signicant changes between the 3
rd
and 15
th
min of exercise.
Discussion
Paragraph 17. This study is the rst comparison of sustained
(15 min) UR vs DR performed at steep slope (± 15%) either at
similar running speed or at similar oxygen uptake in well-
trained athletes. The main ndings of this study are: i) cardior-
espiratory responses are dramatically reduced in LDR vs HUR,
but maximal HR and respiratory frequency can be achieved in
HDR despite very submaximal V
̇O
2
(70% V
̇O
2max
); ii) greater
slow components of V
̇O
2
, HR, V
̇
E
and respiratory frequency
occurred in HDR vs HUR or LDR; iii) muscular fatigue developed
in lower limbs extensor muscles specically after HDR; iv) spa-
tiotemporal parameters of the running gait are mechanical and
metabolic intensity-dependent but remained constant
throughout each trial.
Specicity of cardiorespiratory responses to downhill vs
uphill running
Paragraph 18. When comparing HUR vs LDR at steep slopes (±
15%) (similar running speed, 6.2 km·h
−1
), 25% to 70% lower
cardiorespiratory responses, together with reduced b[La] were
observed in LDR. This observation is in line with the reduced
metabolic cost of DR of trained runners at this slope (Lemire
et al., 2018) and extend previous ndings collected during
shorter duration running trials with smaller slope (5 min at ±
5%) (Kolkhorst et al., 1996). However, when comparing HUR
and HDR at steep slope (± 15%) (similar oxygen uptake), much
higher running speed was achieved in HDR (18.9 vs 6.2 km·h
−1
)
together with greater HR and V
̇
E
(Figures 3(b) and 4(a)). The
Figure 4. Time course of the ventilatory responses during the 15 min trials. Panel a, pulmonary ventilation; panel b, respiratory frequency; panel c, tidal volume. Black
symbols: DR at 70% V
̇O
2max
(HDR); white symbols: UR at 70% V
̇O
2max
(HUR); grey symbols: DR at the same running speed than UR (LDR). Horizontal dashed lines indicate
maximal values measured during the level running incremental test. Values are means ± SD of 8 athletes.
6M. LEMIRE ET AL.
greater V
̇
E
response observed in HDR was associated with
a higher respiratory frequency, suggesting a more supercial
ventilation pattern (Figure 4(a,b)) but Ti/Ttot ratio was not
altered, indicating that the relative contribution of inspiration
and expiration phases into the ventilation cycle was unchanged
in HDR vs HUR. The exacerbated HR and ventilatory responses
progressively developed throughout the 15 min HDR trial led to
maximal HR and maximal respiratory frequency despite sub-
maximal V
̇O
2
(70% V
̇O
2max
, Figure 3). Our athletes approached
the upper limit of their running capacity at the end of the HDR
trial and pilot works demonstrated that most of them would
not have been able to complete a 15 min DR trial performed at
80% V
̇O
2max
, despite 4 familiarization sessions in DR. Given the
lower V
̇O
2max
recently reported in highly trained athletes
during DR at −15% slope (Lemire et al., 2020b), the HDR trial
in the present study was performed at higher relative metabolic
intensity (84% of condition-specic V
̇O
2max
), possibly contribut-
ing to the higher HR and V
̇
E
responses observed in HDR vs HUR,
despite similar absolute metabolic intensity (V
̇O
2
in l·min
−1
).
Paragraph 19. Collectively, the present results suggest that
the HR/V
̇O
2
response to DR is dierent than the one observed
for UR, supporting a dierent coupling of the cardiovascular
and metabolic responses during DR vs UR (Figure 7(a)). This
possibility is in line with previous reports comparing UR vs DR
(Kolkhorst et al., 1996) or eccentric vs concentric cycling
(Dufour et al., 2007, 2004; Lipski et al., 2018). Of note, blood
lactate was signicantly higher at the 1
st
and 3
rd
min of recov-
ery after HDR vs HUR despite similar exercise V
̇O
2
. This
Figure 5. Maximal isometric strength measured pre and post trials. Hip extensor (Panel a), knee extensor (Panel b) and plantar flexor (Panel c). DR at 70% V
̇O
2max
(HDR);
UR at 70% V
̇O
2max
(HUR); DR at the same running speed than UR (LDR). * p < 0.05 pre vs post in HDR. Values are means ± SD of 8 athletes.
JOURNAL OF SPORTS SCIENCES 7
observation suggests that HDR might require a greater contri-
bution of anaerobic glycolysis to total energy turnover, albeit
remaining somewhat modest (b[La] = ~3.3 mmol·l
−1
) as it did
not lead to greater CO
2
production (i.e., via increased buer
activity) in HDR vs HUR conditions (Figure 7(c)). Although the
physiological tenets of the specic HR and ventilation pattern
observed in DR vs UR remain unclear, they might be related to
a combination of several factors pertaining to DR such as
increased eccentric muscle actions, higher running velocities,
exacerbated muscle work for trunk stabilization and/or altered
locomotor/ventilation coupling with cardiovascular and venti-
latory consequences.
Rapid and slow components of the cardiorespiratory
responses during downhill vs uphill running
Paragraph 20. After rapid initial responses from exercise onset,
V
̇O
2
, V
̇
E
, respiratory frequency and tidal volume remained
stable between 3
rd
and 15
th
min in HUR and LDR (Figures 3
and 4). Conversely, despite its 3 times faster-running speed,
V
̇O
2
was lower (−300 ml·min
−1
) after 3 min of exercise during
HDR vs HUR, and progressively increased between 3
rd
and 15
th
min during HDR, describing a slow component (+371 ml·min
−1
),
which also occurred for HR (+22 bpm), V
̇
E
(+24 l·min
−1
) and
respiratory frequency (+9 breaths·min
−1
). These observations
suggest our athletes incurred a larger O
2
decit in the rst
3 min of the HDR vs HUR trial, despite similar end-exercise
V
̇O
2
and similar V
̇O
2
averaged over the 3
rd
to 15
th
min time
window. These results extend previous ndings showing simi-
lar V
̇O
2
kinetics in eccentric vs concentric cycling performed at
much lower metabolic intensity (~26% V
̇O
2max
) (Perrey et al.,
2001) and also add on recent observations that V
̇O
2
kinetics
during LR and UR are correlated in elite mountain runners
(Willis et al., 2019). The physiological mechanisms underlying
the progressively increasing cardiorespiratory responses in HDR
could be related to the higher relative metabolic exercise
intensity in HDR (84% of DR V
̇O
2max
) vs HUR (68% UR V
̇O
2max
)
(Lemire et al., 2020b) and/or to the greater mechanical con-
straints associated with DR presumably impairing O
2
delivery
(i.e., greater vascular collapse during muscle actions) and/or
increasing O
2
demand as lower leg muscles fatigue (i.e., altered
muscle recruitment) (Poole, 2019).
Lower limbs muscular fatigue in downhill vs uphill
running
Paragraph 21. Signicant torque losses were observed in the
knee and hip extensors (range −11 to −15%) only after HDR
(Figure 5). Of note, none of these strength measures signi-
cantly correlated to the cardiorespiratory responses, including
the magnitude of the slow components. The torque losses
observed after 15-min DR at 70% V
̇O
2max
in the present
study are in line with previous reports showing depressed
knee extensor isometric torque (−15%) after 30-min DR
(10 km·h
−1
at −20% slope) (Martin et al., 2004) or reduction
in knee extensors isometric torque (−19%) after an 8.5 km
mostly downhill trail run (~34 min duration, about −17%
slope with running speed ranging from 11 to 19 km·h
−1
)
(Giandolini et al., 2016a).
This attenuated torque after HDR could be mainly ascribed
to the deleterious eect of lower limb mechanical loading, as
oxygen uptake (i.e. metabolic load) was globally similar to HUR.
Muscle damage have been repeatedly reported to contribute
to muscular dysfunction after DR (Giandolini et al., 2016b),
therefore their involvement in the present results cannot be
ruled out but their role was probably minimal as our subjects
were used to perform trail races/training and all realized 4
specic familiarization sessions to treadmill DR. Whatever the
Figure 6. Stride length (Panel a), stride frequency (Panel b) and contact time (Panel c) measured at the 3
rd
and 15
th
min in each trial. DR at 70% V
̇O
2max
(HDR); UR at
70% V
̇O
2max
(HUR); DR at the same running speed than UR (LDR). * p < 0.05 vs HDR and $ p < 0.05 vs HUR at same time points. Values are means ± SD of 8 athletes.
8M. LEMIRE ET AL.
Figure 7. Relationships between heart rate (Panel a), ventilation (panel b), carbon dioxide production (Panel c) and oxygen uptake respectively. Black symbols: DR at
70% V
̇O
2max
(HDR); white symbols: UR at 70% V
̇O
2max
(HUR); grey symbols: DR at the same running speed than UR (LDR). * p < 0.05 vs linear regression slope in LDR, ¤
p < 0.05 vs linear regression slope in HDR and # p < 0.05 vs linear regression intercept in HUR. Values are means ± SD of 8 athletes.
JOURNAL OF SPORTS SCIENCES 9
exact underlying mechanisms, the reduction in extensor mus-
cle torque observed after HDR supports the recent proposition
that lower limb muscle strength contributes to incline running
performance (Lemire et al., 2020a) as encountered during trail
or road races.
Running kinematics in downhill vs uphill running
Paragraph 22. Despite similar running speed (6.2 km·h
−1
), HUR
elicited higher stride frequency, shorter stride length and
shorter contact time compared to LDR (Figure 6) in line with
previous observations collected from ± 5 to 15% slope
(Gottschall & Kram, 2005; Minetti et al., 1994). When compared
at similar V
̇O
2
(~2.900 l·min
−1
), HDR (18.9 km·h
−1
) induced 2.5
times longer stride length, higher stride frequency and more
than 2 times shorter contact time compared to HUR
(6.2 km·h
−1
). To our knowledge, this is the rst kinematic
description of DR vs UR gait at severe slope (±15%) combined
with similar but high metabolic intensity (i.e., especially in DR)
in well-trained athletes.
Within each trial, we observed stable running gaits between
the 3
rd
and 15
th
min, even during HDR where signicant max-
imal isometric muscle torque losses were identied. Therefore,
running gait during DR at 70% V
̇O
2max
with −15% slope can be
preserved for 15-min by well-trained athletes despite signi-
cant lower limb extensor muscle torque losses and signicant
cardiorespiratory slow components.
Limitations
Paragraph 23. The running speed used during HUR and HDR
to achieve 70% of level running V
̇O
2max
have been deter-
mined using previously performed maximal incremental
tests using 2-min stages at the same slopes (+15/-15%). This
method does not allow to anticipate the development of slow
components in the cardiorespiratory responses but the
observation of similar end-exercise and average V
̇O
2
in HUR
vs HDR suggests our objective of similar V
̇O
2
among condi-
tions was reached. The assessments of lower limb muscle
strength were not performed with a gold-standard isokinetic
ergometer but instead with a handheld dynamometer.
Although such device may have accuracy limitations, it has
been validated in the literature against isokinetic ergometry
and we implemented specic positions of both the investi-
gator and the subject during each evaluation to secure accu-
rate measurements. In the same line, although limited, our
number of subjects (N = 8) was determined after sample size
calculation to ensure a statistical power > 0.9 and an alpha
risk < 0.05. Lastly, our calculations of cardiorespiratory slow
components over the 15-min running trials were not based
on parameters of V
̇O
2
on-kinetics modelizations but rather on
the dierence between end-exercise and the 3
rd
minute value
(Poole & Jones, 2012). We are condent this approach is
appropriate to highlight the absence of steady-state
observed in the HDR condition and opens the way for future
characterization of proper V
̇O
2
on-kinetics in inclined vs level
running conditions.
Paragraph 24. In conclusion, cardiorespiratory
responses to DR vs UR heavily depend on both metabolic
(i.e., oxygen uptake) and mechanical exercise intensity (i.e.,
running speed). At similar running speed, cardiorespiratory
responses are attenuated in DR vs UR, with no signicant
impairment in muscular function but altered running gait
kinematic. During high intensity running exercise and
despite similar oxygen uptake, cardiorespiratory responses
are exacerbated in DR vs UR, with signicant reductions in
lower limb extensor muscle torque and markedly dierent
running kinematics. Of note, DR running at 70% V
̇O
2max
sustained for 15 min at −15% slope led HR and respiratory
frequency to maximal values in well-trained athletes. These
results demonstrate that high intensity DR sessions at
−15% slope can hardly be performed above 70% of
V
̇O
2max
in competitive trailers.
Acknowledgements
The authors thank the athletes for their willingness to participate in the
present work. They also warmly thank the whole Respiratory and
Functional Exploration department of Strasbourg’s New Civil Hospital.
Compliance with ethical standards
The experiment was previously approved by our Institutional Review Board
and complied with the Declaration of Helsinki (CPP18-039a/2108-A00700-55).
Disclosure statement
No conicts of interest, nancial or otherwise, to declare by the authors.
Funding
No funding was received for this study.
ORCID
Marcel Lemire http://orcid.org/0000-0002-8023-0329
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2018-0365
JOURNAL OF SPORTS SCIENCES 11
... Environmental conditions have also been studied as a risk factor associated with the occurrence of EAH in long mountain races, especially when temperatures are extremely cold or warm [23,88,89]. Chlibkoval et al. [56] found no cases of EAH in an observational study conducted in extreme cold (−7.96 to −20 • C), but with a small elevation gain (764 m). ...
... Another factor that has been highlighted to explain the association between EAH and AKI through rhabdomyolysis in these races is the large cumulative elevation gains [89]. Race mechanics involving a major eccentric component of muscle contraction could result in rhabdomyolysis through the increase in CK and other inflammation markers and muscle destruction. ...
... However, CK increases were not seen in all the analyzed ultra-trail races, the values were very variable, and the peaks were found at different moments during the races, even in very flat events. The absence of muscular damage markers and rhabdomyolysis could be due to a slower race pace, which would compensate for the eccentric component of steep descents [89]. An example which illustrates that greater elevation gains/losses do not imply greater increases in SCR or CK is the observational study by Belli et al. [51], carried out in a single-stage 217 km race and with an elevation gain of 12,200 m. ...
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Abstract: Background and objectives: Ultra-trail races can cause episodes of acute kidney injury (AKI) and exercise-associated hyponatremia (EAH) in healthy subjects without previous renal pathology. This systematic review aims to review the incidence of these two syndromes together and separately taking into account the length and elevation of the ultra-trail race examined. Materials and Methods: A systematic review was conducted through electronic search in four electronic databases (PubMed, EBSCO, Web of Science and Alcorze). Results: A total of 1127 articles published between January 2006 and December 31, 2021 were included, 28 of which met the inclusion criteria. The studies were categorized according to the length and stages of the race in four categories: medium (42 to 69 km), long (70 to 99 km), extra (>100 km) and multi-stage if they included various stages. A total of 2950 runners (666 females and 2284 males) were extracted from 28 publications. The AKI incidence found was 42.04% (468 cases of 1113), and 195 of 2065 were diagnosed with EAH, accounting for 9.11%. The concurrence of both pathologies together reached 11.84% (27 individuals) from a total of 228 runners with AKI and EAH simultaneously analyzed. Sorted by race category, the AKI+EAH cases were distributed as follows: 18 of 27 in the extra (13.63% and n = 132), 4 in the large (5.79% and n = 69) and 5 in the medium category (18.15% and n = 27). Conclusions: According to these results, extra and medium races showed a similar incidence of AKI+EAH. These findings underline the importance of the duration and intensity of the race and may make them responsible for the etiology of these medical conditions. Due to their variable incidence, EAH and AKI are often underdiagnosed, leading to poorer prognosis, increased condition seriousness and hindered treatment. The results of this review urge participants, coaches and race organizers to take measures to improve the early diagnosis and urgent treatment of possible EAH and AKI cases.
... Our results thus contribute to postulate that a greater respiratory function decay is expected following a MUM compared to a flat ultramarathon. As MUM athletes have to confront uphill and downhill running on uneven surfaces, higher ventilatory requirements (Lemire et al., 2021;Vernillo et al., 2014) and increased postural stabilizing demands placed upon respiratory muscles (Bernardi et al., 2017;Degache et al., 2018;Marcolin et al., 2016) appear to be the main reasons explaining such difference. Conversely, altitude exposure, unlike previous studies conducted in the Alps (Vernillo et al., 2014;Wuthrich et al., 2015), do not appear to have played a key role in the observed respiratory function decay. ...
... Therefore, runners and coaches should consider that inspiratory muscle function could constitute a performance factor in MUM and thus the addition of specific MIP training into their daily routine might improve their race results (Karsten et al., 2018;Mickleborough et al., 2010;Tiller, 2019;Vernillo et al., 2015;Wuthrich et al., 2015). Indeed, as respiratory muscles play an important role regarding trunk stability (Gandevia et al., 2002;Janssens et al., 2010;Tong et al., 2014) and post-MUM reductions in static and dynamic postural control have been documented (Degache et al., 2018;Marcolin et al., 2016), a better muscle inspiratory capacity may minimize the risk of fall and improve, among other factors, ventilatory efficiency and running economy in the last segments of those races (Bernardi et al., 2017;Lemire et al., 2021;Tiller, 2019;Tiller et al., 2019;Vernillo et al., 2015;Wuthrich et al., 2015). ...
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The study aimed to provide within-race data on the time course of pulmonary function during a mountain ultramarathon (MUM). Additionally, we wanted to assess possible sex differences regarding pre-to post-race change in pulmonary and inspiratory muscle function. Lastly, we were interested in evaluating whether changes in respiratory function were associated with relative running speed and due to general or specific fatigue. 47 athletes (29 males and 18 females; 41 ± 5 years) were submitted to a cardio-pulmonary exercise test (CPET) before a 107-km MUM. Spiro-metric variables: forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), FEV1/FVC and peak expiratory flow (PEF); maximal inspiratory pressure (MIP); squat jump (SJ) and handgrip strength (HG) were assessed before and after the race. Additionally PEF was measured at three aid stations (33 rd , 66 th and 84 th km) during the race. PEF declined from the 33 rd to the 66 th km (p = 0.004; d = 0.72) and from the 84 th km to the finish line (p = 0.003; d = 0.90), while relative running speed dropped from the first (0-33 km) to the second (33-66 km) race section (p < 0.001; d = 1.81) and from the third (66-84 km) to the last race section (p < 0.001; d = 1.61). Post-race, a moderate reduction was noted in FVC (-13%; p < 0.001; d = 0.52), FEV1 (-19.5%; p < 0.001; d = 0.65), FEV1/FVC (-8.4%; p = 0.030; d = 0.59), PEF (-20.3%; p < 0.001; d = 0.58), MIP (-25.3%; p < 0.001; d = 0.79) and SJ (-31.6%; p < 0.001; d = 1.42). Conversely, HG did not change from pre-to post-race (-1.4%; p = 0.56; d = 0.05). PEF declined during the race in parallel with running speed drop. No sex differences were noted regarding post-race respiratory function , except that FEV1/FVC decay was significantly greater among women. The magnitude of pre-to post-race respiratory function decline was uncorrelated with relative running speed.
... The importance of strength training for improving running economy on level [i.e., track (Paavolainen et al., 1999), marathon (Jones, 2006), or triathlon (Millet et al., 2002)] running has been known for a long time, but to our knowledge, this study is the first to report such a correlation between downhill ECR and the KE strength. Downhill running exacerbates lower limb neuromuscular fatigue (Giandolini et al., 2016), and especially KE fatigue (e.g., −15% torque after 15 min at −15% slope) (Lemire et al., 2020b). This high level of muscle activation can induce severe lower limb tissue damage, indirectly evidenced by increases in plasma creatine kinase and myoglobin concentrations or inflammatory markers associated Symbols "+" for 0%, ↓ for ±5%, υ for ±10%, υ for +15% and υ for ±20%; † indicate a statistically significant correlation (p < 0.05). ...
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The aim of this study was first to determine if level, uphill and downhill running energy cost (ECR) values were correlated at different slopes and for different running speeds; and second to determine the influence of lower limb strength on ECR. Twenty-nine healthy subjects completed a randomized series of 4-min running bouts on an instrumented treadmill to determine their cardiorespiratory and mechanical (i.e., ground reaction forces) responses at different constant speeds (8, 10, 12, and 14 km·h-1) and different slopes (-20, -10, -5, 0, +5, +10, +15 and +20%). The subjects also performed a knee extensor strength assessment. Oxygen and energy costs of running values were correlated between all slopes by pooling all running speeds (all r² ≥ 0.27; p ≤ 0.021), except between steepest uphill vs level and steepest downhill slope (i.e., +20% vs 0% and -20% slopes; both p ≥ 0.214). When pooled across all running speeds, the ECR was inversely correlated with knee extensor isometric maximal torque only in level and downhill running conditions (all r² ≥ 0.24; p ≤ 0.049), except for the steepest slope (i.e., -20%). The optimal downhill grade (i.e., lowest oxygen cost) varied between running speeds and ranged from -14% and -20% (all p < 0.001). The present results suggest that on ~±20% slope, running energetics are determined by different factors (i.e., reduced bouncing mechanism, muscle higher strength in negative slope vs. higher cardiopulmonary fitness level in positive slope) than on shallow slopes. At lower negative slopes and in level running, knee extensor strength is related to ECR.
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Backgroud: The calcium phosphate biomaterials have excellent bone inductivity, exercise can promote the bone formation of biomaterials in animals, but it is not clear which exercise mode is better. Objective: To explore the effect of different exercise modes on osteoinduction by calcium phosphate-based biomaterials which were implanted in mice. Method: The collagen-thermosensitive hydrogel-calcium phosphate (CTC) composite was prepared and transplanted in the thigh muscle of mice, then all mice were divided randomly into four groups (n = 10): the uphill running group, the downhill running group, the swimming group and the control group (conventional breeding). Ten weeks later, the samples were harvested, fixed, decalcified, embedded in paraffin and stained with hematoxylin and eosin (H&E), and then the osteoinduction phenomenon was observed and compared through digital slice scanning system. The area percentage of new bone-related tissues and the number of osteocytes and chondrocytes were counted and calculated. Lastly, the immunohistochemistry of type I collagen (ColI) and osteopontin (OPN) was performed to identify the new bone tissues. Results: The area percentage of new bone-related tissues and the number of osteocytes and chondrocytes were positively correlated; ordering from most to least of each group were as followings: the uphill running group > the swimming group > the downhill running group > the control group. The immunostaining of ColI and OPN results showed that both of the two proteins were identified in the new bone tissues, indicating that the CTC composite could induce ectopic bone formation in mice, especially training for uphill running and swimming. Conclusion: Our results show that uphill running or swimming is a form of exercise that is beneficial to osteogenesis. According to this, we propose treatment with artificial bone transplantation to patients who suffer from bone defects. Patients should do moderate exercise, such as running uphill on the treadmill or swimming.
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Objectives: Recent studies investigated the determinants of trail running performance (i.e., combining uphill (UR) and downhill running sections (DR)), while the possible specific physiological factors specifically determining UR vs DR performances (i.e., isolating UR and DR) remain presently unknown. This study aims to determine the cardiorespiratory responses to outdoor DR vs UR time- trial and explore the determinants of DR and UR performance in highly trained runners. Design: Randomized controlled trial. Method: Ten male highly-trained endurance athletes completed 5-km DR and UR time-trials (average 9 grade: ±8%) and were tested for maximal oxygen uptake, lower limb extensor maximal strength, local muscle endurance, leg musculotendinous stiffness, vertical jump ability, explosivity/agility and sprint velocity. Predictors of DR and UR performance were investigated using correlation and commonality regression analyses. Results: Running velocity was higher in DR vs UR time-trial (20.4±1.0 vs 12.0±0.5 km·h-1, p<0.05) with similar average heart rate (95±2% vs 94±2% maximal heart rate; p>0.05) despite lower average V̇O2 (85±8% vs 89±7% V̇O2max; p<0.05). Velocity at V̇O2max (vV̇O2max) body mass index (BMI) and maximal extensor strength were significant predictors of UR performance (r²=0.94) whereas vV̇O2max, leg musculotendinous stiffness and maximal extensor strength were significant predictors of DR performance (r²=0.84). Conclusions: Five-km UR and DR running performances are both well explained by three independent predictors. If two predictors are shared between UR and DR performances (vV̇O2max and maximal strength), their relative contribution is different and, importantly, the third predictor appears very specific to the exercise modality (BMI for UR vs leg musculotendinous stiffness for DR).
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Purpose: The purpose of this study was twofold: i) determine if well-trained athletes can achieve similar peak oxygen uptake (VO2peak) in downhill running (DR) versus level (LR) or uphill running (UR), and, ii) investigate if lower limb extensor muscle strength is related to the velocity at VO2peak (vVO2peak) in DR, LR and UR. Methods: Eight athletes (VO2max=68±2 ml·min·kg) completed maximal incremental tests in LR, DR (-15% slope) and UR (+15% slope) on a treadmill (+1, +1.5 and +0.5 km·h every 2 min, respectively) while cardiorespiratory responses and spatiotemporal running parameters were continuously measured. They were also tested for maximal voluntary isometric strength of hip and knee extensors and plantar flexors. Results: Oxygen uptake at maximal effort was ~16-18% lower in DR vs LR and UR (~57±2, 68±2 and 70±3 ml·min·kg, respectively) despite much greater vVO2peak (22.7±0.6 vs 18.7±0.5 and 9.3±0.3 km·h, respectively). At vVO2peak, longer stride length and shorter contact time occurred in DR vs LR and UR (+12%, +119%, -38% and -61%, respectively). Contrary to knee extensor and plantar flexor, hip extensor isometric strength correlated to vVO2peak in DR, LR and UR (r=-0.86 to -0.96, p<0.05). At similar VO2, higher heart rate and ventilation emerged in DR vs LR and UR, associated with a more superficial ventilation pattern. Conclusions: This study demonstrates that well-trained endurance athletes, accustomed to DR, achieved lower VO2peak despite higher vVO2peak during DR vs LR or UR maximal incremental tests. The specific heart rate and ventilation responses in DR might originate from altered running gait and increased lower limb musculotendinous mechanical loading, furthering our understanding of the particular physiology of DR, ultimately contributing to optimize trail race running performance.
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Purpose Exercise economy is not solely an intrinsic physiological trait because economy in one mode of exercise (e.g., running) does not strongly correlate with economy in another mode (e.g. cycling). Economy also reflects the skill of an individual in a particular mode of exercise. Arguably, level, uphill and downhill running constitute biomechanically different modes of exercise. Thus, we tested the hypothesis that level running economy (LRE), uphill running economy (URE) and downhill running economy (DRE) would not be strongly inter-correlated. Methods We measured the oxygen uptakes of 19 male trained runners during three different treadmill running speed and grade conditions: 238 m/min, 0%; 167 m/min, + 7.5%; 291 m/min, − 5%. Mean oxygen uptakes were 46.8 (SD 3.9), 48.0 (3.4) and 46.9 (3.7) ml/kg/min for level, uphill and downhill running, respectively, indicating that the three conditions were of similar aerobic intensity. Results We reject our hypothesis based on the strong correlations of r = 0.909, r = 0.901 and r = 0.830, respectively, between LRE vs. URE, LRE vs. DRE and URE vs. DRE. Conclusion Economical runners on level surfaces are also economical on uphill and downhill grades. Inter-individual differences in running economy reflect differences in both intrinsic physiology and skill. Individuals who have experience with level, uphill and downhill running appear to be equally skilled in all three modes.
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Purpose: Mountain running races are increasingly popular although our understanding of the particular physiology associated with downhill running (DR) in trained athletes remains scarce. This study explores the cardiorespiratory responses to high slope constant velocity uphill running (UR) and DR. Method: Eight endurance athletes performed a maximal incremental test and two 15 min running bouts (UR, +15% or DR, -15%), at the same running velocity (8.5±0.4 km·h-1). Oxygen uptake (V ̇O2), heart rate (HR) and ventilation rates (V ̇E) were continuously recorded and blood lactate (bLa) was measured before and after each trial. Results: DR induced a more superficial, ventilation pattern featuring reduced tidal volume (p < .05, ES = 6.05) but similar respiratory frequency (p > .05, ES = 0.68) despite lower V ̇E (p < .05, ES = 5.46), V ̇O2 (p < .05, ES = 12.68), HR (p < .05, ES = 6.42) and bLa (p < .05, ES = 1.70). A negative slow component was observed during DR for V ̇O2 (p < .05, ES = 1.72) and HR (p < .05, ES = 0.80). Conclusions: These results emphasize the cardiorespiratory responses to DR and highlight the need for cautious interpretation of V ̇O2, HR and V ̇E pattern as makers of exercise intensity for training load prescription and management. Keywords: Inclined treadmill; oxygen uptake; heart rate; pulmonary ventilation
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Purpose: This study compared cardio-pulmonary responses between incremental concentric and eccentric cycling tests, and examined factors affecting the maximal eccentric cycling capacity. Methods: On separate days, nine men and two women (32.6 ± 9.4 years) performed an upright seated concentric (CON) and an eccentric (ECC) cycling test, which started at 75 W and increased 25 W min-1until task failure. Gas exchange, heart rate (HR) and power output were continuously recorded during the tests. Participants also performed maximal voluntary contractions of the quadriceps (MVC), squat and countermovement jumps. Results: Peak power output was 53% greater (P < 0.001, g = 1.77) for ECC (449 ± 115 W) than CON (294 ± 61 W), but peak oxygen consumption was 43% lower (P < 0.001, g = 2.18) for ECC (30.6 ± 5.6 ml kg min-1) than CON (43.9 ± 6.9 ml kg min-1). Maximal HR was not different between ECC (175 ± 20 bpm) and CON (182 ± 13 bpm), but the increase in HR relative to oxygen consumption was 33% greater (P = 0.01) during ECC than CON. Moderate to strong correlations (P < 0.05) were observed between ECC peak power output and CON peak power (r = 0.84), peak oxygen consumption (r = 0.54) and MVC (r = 0.53), while no significant relationships were observed between ECC peak power output and squat as well as countermovement jump heights. Conclusion: Unexpectedly, maximal HR was similar between CON and ECC. Although ECC power output can be predicted from CON peak power output, an incremental eccentric cycling test performed after 3-6 familiarisation sessions may be useful in programming ECC training with healthy and accustomed individuals.
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BACKGROUND: The aims of this study were (a) to examine the effects of a trail mountain race (TMR) on hydration status and neuromuscular performance of recreational trail runners and (b) to determine the relationship among these parameters, subject’s characteristics and competitive performance. METHODS: 35 male recreational trail runners (age, 38.1 ± 9.5 years; height, 177.3 ± 5.8 cm; body mass, 73.8 ± 8.4 kg; mean ± SD) were assessed before and after a 21.1 km TMR. Hydration status (urine color [Ucol] and body mass [BM]) and neuromuscular performance (countermovement jump [CMJ] and rebound jumps [RJ]) were assessed. RESULTS: Significant changes following the TMR included RJ mean contact time (RJMCT) (12%, ES = -0.35, p < 0.05) and dehydration status increases (BM reductions [-2.7%, ES = 0.24, p < 0.001] and Ucol [147% increase, ES = -1.8, p < 0.001]). Low to moderate positive correlations were found between pre- and post-TMR BM (r = 0.5 – 0.54; p < 0.01), post-race Ucol (r = 0.37; p < 0.05), age (r = 0.57; p < 0.01) and TMR performance. Participant’s age combined with Ucol and the RJMJH post-TMR, explained 65% of the variance in the final running time (r = 0.81; p = 0.000). CONCLUSIONS: Participation in a 21.1 km TMR in recreational runners results in small reductions of the neuromuscular function and increases in dehydration levels. The hydration status (Ucol) and the RJMJH post-TMR combined with the runners’ chronological age seemed to be good predictors of the final running performance. http://www.minervamedica.it/en/journals/sports-med-physical-fitness/article.php?cod=R40Y9999N00A16113004
Article
Oxygen uptake (V̇O2), heart rate (HR), energy cost (EC) and oxygen pulse are lower during downhill compared to level or uphill locomotion. However, a change in oxygen pulse and EC during prolonged grade exercise is not well documented. This study investigated changes in cardiorespiratory responses and EC during 45-min grade exercises. Nine male healthy volunteers randomly ran at 75% HR reserve during 45-min exercise in a level (+1%), uphill (+15%) or downhill (−15%) condition. V̇O2 , minute ventilation (V̇E ) and end-tidal carbon dioxide (PetCO2) were recorded continuously with 5-min averaging between the 10th and 15th min (T1) and 40th and 45th min (T2). For a similar HR (157±3 bpm), V̇O2 , V̇E , and PetCO2 were lower during downhill compared to level and uphill conditions (p<0.01). V̇O2 and V̇E decreased similarly from T1 to T2 for all conditions (all p<0.01), while PetCO2 decreased only for the downhill condition (p<0.001). Uphill exercise required greater EC compared to level and downhill exercises. EC decreased only during the uphill condition between T1 and T2 (p<0.01). The lowest V̇O2 and EC during downhill exercise compared to uphill and level exercises suggests the involvement of passive elastic structures in force production during downhill. The lower cardiorespiratory response and the reduction in PetCO2 during downhill running exercise, while EC remained constant, suggests an overdrive ventilation pattern likely due to a greater stimulation of efferent neural factors.
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This review strikes at the very heart of how the microcirculation functions to facilitate blood-tissue oxygen, substrate and metabolite fluxes in skeletal muscle. Contemporary evidence, marshalled from animals and humans using the latest techniques, challenges iconic perspectives little-changed over the past century. Those perspectives include: The presence of contractile or collapsible capillaries in muscle, unitary control by pre-capillary sphincters, capillary recruitment at the onset of contractions and the notion of capillary-to-mitochondrial diffusion distances as limiting O2 delivery. Today a wealth of physiological, morphological and intravital microscopy evidence presents a completely different picture of microcirculatory control. Specifically, capillary red blood cell (RBC) and plasma flux is controlled primarily at the arteriolar level with most capillaries, in healthy muscle, supporting at least some flow at rest. In healthy skeletal muscle this permits substrate access (whether carried in RBCs or plasma) to a prodigious total capillary surface area. Pathologies such as heart failure or diabetes decrease access to that exchange surface by reducing the proportion of flowing capillaries at rest and during exercise. Capillary morphology and function vary disparately among tissues. The contemporary model of capillary function explains how, following the onset of exercise, muscle O2 uptake kinetics can be extremely fast in health but slowed in heart failure and diabetes impairing contractile function and exercise tolerance. Adoption of this model is fundamental for understanding microvascular function and dysfunction and, as such, to the design and evaluation of effective therapeutic strategies to improve exercise tolerance and decrease morbidity and mortality in disease.
Aim: The purpose of this brief report was to examine the net oxygen cost, oxygen kinetics, and kinematics of level and uphill running in elite ultra-trail runners. Methods: Twelve top-level ultra-distance trail runners performed two 5-minute stages of treadmill running (level, 0%, men 15 km·h-1, women 13 km·h-1; and uphill, 12%, men 10 km·h-1, women 9 km·h-1). Gas exchanges were measured to obtain the net oxygen cost and assess oxygen kinetics. Additionally, running kinematics were recorded with inertial measurement unit motion sensors on the wrist, head, belt, and foot. Results: Relationships resulted between level and uphill running regarding oxygen uptake, respiratory exchange ratio, net energy and oxygen cost, as well as oxygen kinetics parameters of amplitude and time delay of the primary phase, and time to reach V̇O2 steady state. Of interest, net oxygen cost demonstrated a significant correlation between level and uphill conditions (r=0.826, p<0.01). Kinematics parameters demonstrated relationships between level and uphill running as well (including contact time, aerial time, stride frequency, and stiffness; all p<0.01). Conclusion: This study indicated strong relationships between level and uphill values of net oxygen cost, the time constant of the primary phase of oxygen kinetics, and biomechanical parameters of contact and aerial time, stride frequency, and stiffness in elite mountain ultra-trail runners. These results show that these top-level athletes are specially trained for uphill locomotion at the expense of their level running performance and suggest that uphill running is of utmost importance for success in mountain ultra-trail races.
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While previous research has assessed the validity of the OptoGait system to the GAITRite walkway and an instrumented treadmill, no research to date has assessed this system against a traditional three-dimensional motion analysis system. Additionally, previous research has shown that the OptoGait system shows systematic bias when compared to other systems due to the configuration of the system's hardware. The present study examined the agreement between the spatiotemporal gait parameters calculated from the OptoGait system and a three-dimensional motion capture (14 camera Vicon motion capture system and 2 AMTI force plates) in healthy adults. Additionally, a range of filter settings for the OptoGait were examined to determine if it was possible to eliminate any systematic bias between the OptoGait and the three-dimensional motion analysis system. Agreement between the systems was examined using 95% limits of agreement by Bland and Altman and the intraclass correlation coefficient. A repeated measures ANOVA were used to detect any systematic differences between the systems. Findings confirm the validity of the OptoGait system for the evaluation of spatiotemporal gait parameters in healthy adults. Furthermore, recommendations on filter settings which eliminate the systematic bias between the OptoGait and the three-dimensional motion analysis system are provided.