Sustained Muscle Deoxygenation vs. Sustained High VO2 During High-Intensity Interval Training in Sprint Canoe-Kayak

Abstract

Recent data suggests that peripheral adaptations, i.e., the muscle ability to extract and use oxygen, may be a stronger predictor of canoe-kayak sprint performance compared to VO2max or central adaptations. If maximizing the time near VO2max during high-intensity interval training (HIIT) sessions is believed to optimize central adaptations, maximizing the time near maximal levels of muscle desaturation could represent a critical stimulus to optimize peripheral adaptations. Purpose: Therefore, the purpose of this study was to assess the VO2, muscle oxygenation and cardiac output responses to various HIIT sessions, and to determine which type of HIIT elicits the lowest muscle oxygenation and the longest cumulated time at low muscle O2 saturation. Methods: Thirteen well-trained canoe-kayak athletes performed an incremental test to determine VO2max and peak power output (PPO), and 4 HIIT sessions (HIIT-15: 40x[15 s at 115%PPO, 15 s at 30%PPO]; HIIT-30: 20x[30 s at 115%PPO, 30 s at 30%PPO]; HIIT-60: 6x[1 min at 130%PPO, 3 min rest]; sprint interval training (SIT): 6x[30 s all-out, 3 min 30 rest]) on a canoe or kayak ergometer. Portable near-infrared spectroscopy monitors were placed on the Latissimus dorsi (LD), Biceps brachii (BB), and Vastus lateralis (VL) during every session to assess changes in muscle O2 saturation (SmO2, % of physiological range). Results: HIIT-15 and HIIT-30 elicited a longer time >90%VO2max (HIIT-15: 8.1 ± 6.2 min, HIIT-30: 6.8 ± 4.6 min), compared to SIT (1.7 ± 1.3 min, p = 0.006 and p = 0.035) but not HIIT-60 (4.1 ± 1.7 min). SIT and HIIT-60 elicited the lowest SmO2 in the VL (SIT: 0 ± 1%, HIIT-60: 8 ± 9%) compared to HIIT-15 (26 ± 12%, p < 0.001 and p = 0.007) and HIIT-30 (25 ± 12%, p < 0.001 and p = 0.030). SIT produced the longest time at >90% of maximal deoxygenation in all 3 muscles, with effect sizes ranging from small to very large. Conclusions: Short HIIT performed on a canoe/kayak ergometer elicits the longest time near VO2max, potentially conducive to VO2max improvements, but SIT is needed in order to maximize muscle deoxygenation during training, which would potentially conduct to greater peripheral adaptations.

Full text

ORIGINAL RESEARCH
published: 31 July 2019
doi: 10.3389/fspor.2019.00006
Frontiers in Sports and Active Living | www.frontiersin.org 1July 2019 | Volume 1 | Article 6
Edited by:
Franck Brocherie,
Institut national du sport, de l’expertise
et de la performance, France
Reviewed by:
Mohammed Ihsan,
Aspetar Hospital, Qatar
Ben Jones,
University of Essex, United Kingdom
Stylianos N. Kounalakis,
Evelpidon Military Academy, Greece
*Correspondence:
Myriam Paquette
myriam.paquette.2@ulaval.ca
Specialty section:
This article was submitted to
Elite Sports and Performance
Enhancement,
a section of the journal
Frontiers in Sports and Active Living
Received: 16 April 2019
Accepted: 12 July 2019
Published: 31 July 2019
Citation:
Paquette M, Bieuzen F and Billaut F
(2019) Sustained Muscle
Deoxygenation vs. Sustained High
VO2During High-Intensity Interval
Training in Sprint Canoe-Kayak.
Front. Sports Act. Living 1:6.
doi: 10.3389/fspor.2019.00006
Sustained Muscle Deoxygenation vs.
Sustained High VO2During
High-Intensity Interval Training in
Sprint Canoe-Kayak
Myriam Paquette 1,2
*, François Bieuzen 2and François Billaut 1,2
1Département de kinésiologie, Université Laval, Quebec, QC, Canada, 2Institut National du sport du Québec, Montreal, QC,
Canada
Recent data suggests that peripheral adaptations, i.e., the muscle ability to extract
and use oxygen, may be a stronger predictor of canoe-kayak sprint performance
compared to VO2max or central adaptations. If maximizing the time near VO2max during
high-intensity interval training (HIIT) sessions is believed to optimize central adaptations,
maximizing the time near maximal levels of muscle desaturation could represent a critical
stimulus to optimize peripheral adaptations.
Purpose: Therefore, the purpose of this study was to assess the VO2, muscle
oxygenation and cardiac output responses to various HIIT sessions, and to determine
which type of HIIT elicits the lowest muscle oxygenation and the longest cumulated time
at low muscle O2saturation.
Methods: Thirteen well-trained canoe-kayak athletes performed an incremental test to
determine VO2max and peak power output (PPO), and 4 HIIT sessions (HIIT-15: 40x[15 s
at 115%PPO, 15 s at 30%PPO]; HIIT-30: 20x[30 s at 115%PPO, 30 s at 30%PPO];
HIIT-60: 6x[1 min at 130%PPO, 3 min rest]; sprint interval training (SIT): 6x[30 s all-out,
3 min 30 rest]) on a canoe or kayak ergometer. Portable near-infrared spectroscopy
monitors were placed on the Latissimus dorsi (LD), Biceps brachii (BB), and Vastus
lateralis (VL) during every session to assess changes in muscle O2saturation (SmO2,
% of physiological range).
Results: HIIT-15 and HIIT-30 elicited a longer time >90%VO2max (HIIT-15:
8.1 ±6.2 min, HIIT-30: 6.8 ±4.6 min), compared to SIT (1.7 ±1.3 min, p=0.006 and
p=0.035) but not HIIT-60 (4.1 ±1.7 min). SIT and HIIT-60 elicited the lowest SmO2in
the VL (SIT: 0 ±1%, HIIT-60: 8 ±9%) compared to HIIT-15 (26 ±12%, p<0.001 and
p=0.007) and HIIT-30 (25 ±12%, p<0.001 and p=0.030). SIT produced the longest
time at >90% of maximal deoxygenation in all 3 muscles, with effect sizes ranging from
small to very large.
Conclusions: Short HIIT performed on a canoe/kayak ergometer elicits the longest time
near VO2max, potentially conducive to VO2max improvements, but SIT is needed in order
to maximize muscle deoxygenation during training, which would potentially conduct to
greater peripheral adaptations.
Keywords: oxygen saturation, peripheral adaptations, aerobic fitness, sprint kayak, sprint canoe, interval training

Paquette et al. Muscle Oxygenation During HIIT in Kayakers
INTRODUCTION
High-intensity interval training (HIIT) is considered one of the
most effective training for improving performance in athletes
from various sports (Buchheit and Laursen, 2013a). HIIT
involves alternating short (<45 s) to long (2–4 min) bouts of
high-intensity (usually >85% max HR) exercise with recovery
periods (Weston et al., 2014). In the early 2000s, little was
known on the optimal type of HIIT program for producing
the greatest improvement in endurance performance in trained
athletes (Laursen and Jenkins, 2002). Since then, a lot of research
has focused on understanding the acute and chronic effects of
different forms of HIIT to optimize its prescription in athletes.
In 1986, Wenger and Bell (1986) published a review of the
literature, where they concluded that VO2max enhancement was
positively related to exercise intensity, for intensities from 50 to
100% of VO2max, and showed that the greatest improvements
occurred when training was performed at an intensity between
90 and 100% of VO2max. It led several authors to suggest that
training near or at VO2max is an optimal stimulus to improve
VO2max (Billat, 2001). From a physiological perspective, training
at or near VO2max would impose a maximal stress to the
physiological processes and structures limiting VO2max and
should, therefore, promote adaptations in these structures and
processes. For example, it has been shown that mechanical
overload, the main stimulus for morphological adaptation of
the myocardium and hence enhancement of the cardiac output,
is maximal when exercising at the intensity eliciting VO2max
(Åstrand et al., 1964). Thus, there has been great research interest
in characterizing time spent at or near (>90%) VO2max in
different training protocols, to identify the training sessions that
would elicit the longest time near VO2max. In a literature review
published in 2006, Midgley and McNaughton (2006) detailed
the training characteristics that produce the longest time at
or near VO2max. They concluded that, in order to maximize
time spent near VO2max, work intervals of 15–30 s should be
performed at an intensity of 90–105% of the minimal speed
eliciting VO2max (vVO2max), and recovery intervals of 15–30 s
should be performed at an intensity between 50% of VO2max and
lactate threshold.
Sprint interval training (SIT), consisting of low volume all-out
supramaximal (at a greater intensity than 100% VO2max) sprints
of typically 20–30 s duration, interspersed by long (≥2 min)
recovery intervals has been shown to improve endurance
performance in trained cyclists (Laursen et al., 2002) and runners
(Esfarjani and Laursen, 2007). Although time spent at >90%
VO2max during SIT sessions is low (typically 0–60 s in trained
cyclists for an entire training session), it has been suggested
that muscle O2demand is high, especially as the number of
sprints increases, as suggested by low muscle oxygenation levels
(Buchheit et al., 2012a). Therefore, SIT appears to be an optimal
training stimulus to improve endurance performance through
peripheral (muscular) adaptations. But all-out SIT is associated
with high neuromuscular fatigue (Buchheit and Laursen, 2013b),
which could limit the ability of the athletes to perform other
training sessions. It is currently unknown if supramaximal efforts
of lower intensity (120–130% maximal aerobic power) but longer
duration (>45 s) could elicit the same peripheral demand, while
inducing less neuromuscular fatigue. If so, it would be of great
interest for athletes, decreasing the likeliness of interference
between HIIT and other training sessions (moderate-intensity
continuous training, strength training, speed training, power
training, etc.). To our knowledge, acute response to longer
supramaximal interval training has not been assessed so far.
In sprint canoe-kayak, Olympic individual events are 200- and
500-m (∼38 to ∼120 s) for women and 200-m and 1,000-m (∼34
to ∼220 s) for men. While VO2max is often considered a major
performance factor in longer distance sprint canoe-kayak events
(Michael et al., 2008), results from a recent study suggest that
peripheral adaptations (as assessed via near infrared spectroscopy
(NIRS) derived changes in muscle oxygenation) may be stronger
predictors of canoe-kayak performance in both short and long
events (Paquette et al., 2018). In fact, since 200 and 500-m
events are performed at an intensity greater than VO2max, and
since canoe-kayak is an upper body dominant sport, and skeletal
muscles in the arms typically display larger cross sectional area
of type II muscle fibers, it makes this discipline more reliant on
muscle power than cardiorespiratory fitness. Therefore, there is
a need to identify training sessions that elicit a high peripheral
demand in this sport.
The oncoming of affordable and portable NIRS monitors
has increased accessibility to muscle oxygenation measures
during exercise. Researchers have used peak VO2and time
spent >90% VO2max during HIIT sessions to assess the
central demand of HIIT, and we suggest that maximal muscle
deoxygenation and cumulated time at >90% maximal muscle
deoxygenation are good indicators of acute peripheral demand
during HIIT sessions.
The purpose of this study was to assess the VO2, muscle
oxygenation, and cardiac output responses to 4 types of
interval training commonly used by canoe-kayak athletes, and
to determine which type of interval training elicits the lowest
muscle O2levels and the longest cumulated time at low muscle
O2saturation.
METHODS
Subjects
Thirteen canoe-kayak athletes participated in this study, of which
9 were kayakers (3 women, 6 men) and 4 were canoeists (2
women, 2 men). Participants were 22 ±3 years of age (range
19–27 years old) and weighted 71.5 ±8.3 kg. Four of them were
members of the Canadian National Team in sprint or slalom,
and nine were provincial-level athletes in sprint canoe or kayak.
This study was approved by the local ethics committee and
was conducted in accordance to the principles established in
the Declaration of Helsinki, with verbal and written informed
consent provided by all participants.
Experimental Design
Athletes performed a maximal incremental test on a canoe or
kayak, for the determination of maximal oxygen consumption
(VO2max), maximal cardiac output (Qmax), and peak power
output (PPO). Next, they completed four interval training
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Paquette et al. Muscle Oxygenation During HIIT in Kayakers
sessions on a canoe or kayak ergometer in a randomized order to
determine the acute physiological response associated with each
interval training type.
Methodology
Maximal Incremental Test
All participants performed a continuous incremental VO2max
testing consisting of six 2-min stages of increasing intensity
on a kayak or canoe ergometer (SpeedStroke Gym, KayakPro,
Florida, USA). The ergometer was calibrated before each test,
according to the manufacturer recommendations and tension in
the ergometer’s ropes was verified regularly (Tanner and Gore,
2013). Participants received stroke-by-stroke feedback during the
test and were asked to maintain a constant intensity that would
elicit effort perception of 2, 4, 5, 6, 8, and 10/10 during stages 1–6,
respectively. Stroke rate ranges were given for the first 5 stages for
canoe (30–35; 35–40; 40–45; 45–50; 50–55 strokes per min) and
kayak (60–65; 65–75; 75–85; 85–95; 95–105 strokes per min) to
help athletes select the right intensity in each stage. Power output
(PO) was recorded on a computer, using the eMonitorPro2
software (KayakPro, Florida, USA).
Interval Training Sessions
The athletes completed four different HIIT sessions on the canoe
or kayak ergometer in a randomized order. There was always
more than 24 h and less than a week between HIIT sessions and
athletes must refrain from doing any intense physical activity for
24 h before the training session. Training sessions are described
in Table 1. Athletes were asked to rate their level of exertion and
their level of enjoyment on a scale of 1 to 10 at the end of every
HIIT session.
VO2and Cardiac Output
During all sessions, expired air was continuously recorded
using a breath-by-breath gas analyzer (Vmax Encore metabolic
cart, CareFusion Corp, California, USA). PPO was the average
power output on the last 2-min stage of the maximal
incremental test. Heart rate (HR) and cardiac output (Q) were
evaluated during all tests using thoracic electrical bioimpedance
(Physioflow, Manatec Biomedical, France). All devices were
calibrated according to manufacturer guidelines before every test.
Arteriovenous O2difference [(a-v)O2-diff (ml/dl)] was calculated
using the following equation: (a-v)O2-diff =VO2(L/min)/Q
(L/min)∗100 and stroke volume (SV) was calculated from Q and
HR. VO2max, maximal Q (Qmax), maximal SV (SVmax), and
maximal (a-v)O2-diff were defined as the highest values achieved
over a 30-s period during the incremental test. Time over 90
and 95% of VO2max, Qmax, and HRmax were calculated for all
sessions. Peak VO2, peak Q and peak HR were also calculated
for each session, and defined as the highest 30-s average for
VO2and Q and highest 5-s average for HR value reached during
the session.
Muscle Oxygenation
During all tests, Moxy NIRS monitors (Fortiori Design,
Minnesota, USA) were placed on three active muscles: latissimus
dorsi (LD)—midpoint between the inferior border of the scapula
and posterior axillar fold (Borges et al., 2015) –, biceps brachii
(BB)—middle of the BB muscle belly (8–12 cm above the elbow
fold)—and vastus lateralis (VL)—distal part of the VL muscle
belly (10–15 cm above the proximal border of the patella)
(Billaut and Buchheit, 2013). NIRS monitors were placed on
the athlete’s dominant side for kayakers, and on the front leg
and opposite BB and LD for canoeists, parallel to the muscle
fiber orientation. They were attached and secured with a double-
sided adhesive disk and an adhesive patch, and covered by a
dark bandage to reduce the intrusion of extraneous light. The
Moxy monitors position was marked on the athlete’s skin to
ensure the monitors were placed on the same site in every testing
session. Skinfold thickness at each site was measured using a
skinfold caliper (Harpenden Ltd) to ensure that the skinfold
thickness was less than half the distance between the emitter and
the detector (25 mm). The raw muscle O2saturation (SmO2)
signal was treated using a smooth spline filter to reduce the
noise created by movement (Rodriguez et al., 2018). During
exercise, SmO2represents the balance between O2delivery and
extraction by the muscle (Ferrari et al., 2011). Minimum and
maximum SmO2were the absolute lowest and highest 5-s average
SmO2reached during any of the HIIT session. Minimum and
maximum SmO2values were determined from the lowest and
highest observed values throughout the entire experiment for
each subject. All SmO2values were then normalized, so that 0
and 100% represent these minimum and maximum SmO2of
the participant, respectively. SmO2values are presented in these
normalized values in the results section and minimum SmO2
will be referred as deoxy max thereafter. As for VO2max and
cardiac output values, time over 90 and 95% of deoxy max
were calculated for all HIIT sessions and defined as the time
spent at a SmO2value of <10% and <5% in this normalized
scale. Time spent above 90 and 95% deoxy max were determined
during both work and rest intervals to obtain a complete picture
of peripheral metabolic disturbances during the given sessions.
Peak muscle deoxygenation (peak deoxy) was calculated for each
muscle during each session, and was defined as the lowest 5-s
average SmO2reached during the session.
Statistical Analysis
Means and standard variations were calculated for physiological
parameters, and ANOVAs with Tukey post-hoc tests were used
to assess differences between groups. Cohen’s d effect sizes (ES)
and 90% confidence intervals were also computed for differences
in means between sessions and ES of 0.2, 0.6, 1.2, and 2.0 were
considered small, moderate, large, and very large differences,
respectively. For the SmO2data, a robust smallest worthwhile
change (SWC) anchor is not evident, therefore the SWC was
calculated using the standardized mean difference of 0.2 between
subject standard deviations (SD).
RESULTS
Athlete’s Characteristics
Participants had a VO2max of 51.8 ±7.7 ml/kg/min, or 3.7 ±0.8
L/min, a maximal cardiac output of 25.4 ±3.5 L/min, a maximal
SV of 147 ±24 ml/beat, a maximal (a-v)O2-diff of 14.5 ±2.0
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Paquette et al. Muscle Oxygenation During HIIT in Kayakers
TABLE 1 | Description of the interval training sessions.
Session Work
duration
Work target
intensity
Recovery duration Recovery target
intensity
Number of
repetitions/set
Number of sets Rest between
sets
HIIT-15 15 s 110% PPO 15 s 30% PPO 20 2 5 min
HIIT-30 30 s 110% PPO 30 s 30% PPO 10 2 5 min
HIIT-60 1 min 130% PPO 3 min Choice 6 1 –
SIT 30 s All-out 3 min 30 Choice 6 1 –
PPO, peak power output; Choice: the athletes could rest passively or paddle slowly.
FIGURE 1 | Average VO2, Q, and HR at the end of each work and rest interval during the four interval sessions. Horizontal dashed lines represent 90% of VO2max,
Qmax and HRmax, respectively.
ml/dl and a maximal heart rate of 194 ±5 bpm. Their PPO during
the incremental test was 122 ±36 W, or 1.69 ±0.45 W/kg.
Cardiorespiratory and Subjective
Responses
Figure 1 displays the average cardiorespiratory parameters at
the end of each work and rest interval for the four training
sessions. Table 2 shows the power output maintained, and the
VO2and cardiac output responses during each HIIT session.
The highest RPE was reached in the SIT session, but it did not
differ statistically from the other sessions RPE ratings. VO2peak
was greater in HIIT-60 compared to HIIT-15 (ES 1.34 [0.62,
2.08], p=0.02), HIIT-30 (ES 1.41 [0.70, 2.14], p=0.01), and
SIT (ES 2.32 [1.49, 3.16], p<0.01). Peak Q was not different
between sessions. Time spent >90% VO2max was higher in
HIIT-15 (ES 1.71 [0.94,2.48], p<0.01) and HIIT-30 (ES 1.74
[0.98,2.50], p<0.01) compared to SIT. HIIT-15 and HIIT-30
also elicited a greater cumulated time at >90% Qmax compared
to SIT (HIIT-15: ES 1.35 [0.46, 2.25], p=0.04, HIIT-30: ES
1.09 [0.30, 1.88], p=0.02) and greater cumulated time >90%
HRmax (HIIT-15: ES 6.39 [4.46, 8.31], p<0.01, HIIT-30: ES 4.19
[2.91, 5.47], p<0.01).
Muscle Oxygenation Response
Figure 2 displays the average SmO2at the end of each work
and rest interval for the four training sessions. Table 3 details
the muscle oxygenation response to the 4 HIIT protocols. BB
deoxy max was greater in SIT compared to HIIT-15 (ES −1.83
[−1.06, −2.59], p=0.02) and HIIT-30 (ES −1.63 [−0.89, −2.38],
p=0.01) and LD deoxy max was greater in SIT compared to
HIIT-15 (ES −1.24 [−0.54, −1.95], p=0.04). VL deoxy max was
greater in both SIT and HIIT-60 compared to HIIT-15 (SIT: ES
3.86 [−2.77, −4.95], p<0.01, HIIT-60: ES 1.79 [−1.03, −2.55],
p<0.01) and HIIT-30 (SIT: ES −3.76 [−2.87, −4.83], p<
0.01, HIIT-60: ES −1.70 [−0.95, −2.45], p<0.01). For all 3
investigated muscles, SIT resulted in the longest time spent near
maximal muscle deoxygenation compared to session HIIT-15.
Specifically in the VL, SIT resulted in the longest time spent at
>90 and 95% maximal VL deoxygenation compared to HIIT-15
and HIIT-30, and to a smaller extent to HIIT-60.
Figure 3 shows the effect sizes and 90% confidence interval
of differences in means between the different sessions for the
time spent near maximal muscle deoxygenation. Clear very large
differences were found for VL between sessions HIIT-15 and SIT
and between sessions HIIT-30 and SIT, and clear large differences
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Paquette et al. Muscle Oxygenation During HIIT in Kayakers
TABLE 2 | Power output, VO2max and cardiac output values during each interval session.
Session HIIT-15 HIIT-30 HIIT-60 SIT
Work intensity (%PPO) 116 ±16 117 ±19 133 ±21 192 ±36
Recovery intensity (%PPO) 32 ±12 29 ±5 18 ±18 23 ±23
Session enjoyment (/10) 6.9 ±2.2 7.0 ±2.2 6.6 ±2.4 7.2 ±2.2
Session RPE (/10) 7.9 ±1.0 8.1 ±1.7 7.5 ±1.8 8.8 ±0.9
Peak VO2(%VO2max) 92 ±5 91 ±5$98 ±4 87 ±5$
Peak HR (%HRmax) 97 ±3 97 ±2 96 ±2 95 ±2
Peak Q (%Qmax) 95 ±8 94 ±6 93 ±9 90 ±7
Cumulated time >90% VO2max (min) 8.1 ±6.2* 6.8 ±4.6* 4.1 ±1.7 1.7 ±1.3
Cumulated time >95% VO2max (min) 4.9 ±5.3* 3.5 ±4.3 2.9 ±1.8 1.0 ±1.0
Cumulated time >90% Qmax (min) 5.6 ±4.4* 4.0 ±2.9* 2.0 ±1.9 1.5 ±1.6
Cumulated time >95% Qmax (min) 2.2 ±2.3 1.8 ±1.6 1.1 ±1.3 0.9 ±1.1
Cumulated time >90% HRmax (min) 16.6 ±2.6*$13.7 ±3.3*$5.3 ±2.3 3.6 ±1.5
Cumulated time >95% HRmax (min) 7.8 ±5.5*$4.8 ±3.3* 1.6 ±1.8 0.4 ±0.8
PPO, peak power output.
$Different from HIIT-60 (p <0.05).
*Different from SIT (p <0.05).
FIGURE 2 | Average SmO2in the BB, LD, and VL at the end of each work and rest interval during the four interval sessions. Horizontal dashed lines represent 10%
SmO2(90% of maximal deoxygenation).
were found for VL between sessions HIIT-15 and HIIT-60, HIIT-
30 and HIIT-60 and between SIT and HIIT-60 and for BB
between sessions HIIT-15 and SIT. Moderate differences were
found for BB between HIIT-15 and HIIT-60 and HIIT-30 and
HIIT-60. Figure 4 shows the individual response for the time
spent near maximal deoxygenation in each HIIT session, for the
canoers and the kayakers.
Difference Between Muscles
Time spent >90% deoxy max was lower in the VL compared to
the LD (ES −2.38 [−3.28, −1.48], p=0.04) and tended to be
lower compared to BB (ES −1.20 [−1.90, −0.50], p=0.07) in
HIIT-30 session. Peak deoxy values were higher in VL compared
to BB and LD for both sessions HIIT-15 and HIIT-30 (all
p<0.01). There was no difference between investigated muscles
for time spent >90% deoxy max or peak deoxy in HIIT-60 and
SIT sessions.
DISCUSSION
Physiological responses to 4 different HIIT sessions were assessed
in well-trained canoe-kayak athletes and the most important
findings were: (1) short interval training sessions (HIIT-15 and
HIIT-30) elicit the most time at high levels of VO2, Q and HR, but
did not elicit high or sustained levels of muscle deoxygenation;
(2) SIT does not elicit much time at high levels of VO2, Q or
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Paquette et al. Muscle Oxygenation During HIIT in Kayakers
TABLE 3 | Muscle oxygenation response to the four interval sessions.
Session HIIT-15 HIIT-30 HIIT-60 SIT
Peak deoxy BB (%)a9±8* 10 ±9* 6 ±7 1 ±2
Peak deoxy LD (%)a9±7* 6 ±7 5 ±7 2 ±4
Peak deoxy VL (%)a26 ±12*$25 ±12*$8±9 0 ±1
Cumulated time >90% deoxy max BB (s) 7.5 ±8.6* 24.7 ±40.5 24.5 ±26.8 44.8 ±40.0
Cumulated time >90% deoxy max LD (s) 8.7 ±15.3* 29.9 ±24.9 33.3 ±37.3 61.2 ±44.8
Cumulated time >90% deoxy max VL (s) 0.0 ±0.0* 0.2 ±0.6* 26.5 ±39.0* 83.2 ±63.1
Cumulated time >95% deoxy max BB (s) 0.6 ±1.1* 6.8 ±0.2 5.1 ±6.0* 17.2 ±13.7
Cumulated time >95% deoxy max LD (s) 0.7 ±1.2* 6.4 ±5.7* 10.1 ±12.0 21.3 ±17.7
Cumulated time >95% deoxy max VL (s) 0.0 ±0.0* 0.0 ±0.0* 9.1 ±24.3* 46.6 ±53.7
aMinimum SmO2during session, presented in normalized units.
$Different from HIIT-60 (p <0.05).
*Different from SIT (p <0.05).
FIGURE 3 | Effect sizes and 90% confidence interval of differences in means
between cumulated time spent >90% maximal deoxygenation in the three
studied muscles. Positive effect size reflects a greater time spent >90% deoxy
max in the first session compared to the second, while negative effect size
reflects a smaller time spent >90% deoxy max in the first session compared to
the second.
HR, but elicit the highest levels of muscle deoxygenation and the
most time spent at high levels of muscle deoxygenation; (3) long
supramaximal interval training (HIIT-60) is an hybrid between
short intervals and SIT, eliciting higher muscle deoxygenation
than short intervals in the VL, and higher VO2peak than SIT.
HIIT and Central Demand
With no surprise, the short interval sessions elicited the highest
time >90% VO2max compared to the other interval sessions. For
short intervals, the ratio of time >90% VO2max on total exercise
time has been shown to be ∼30% (Buchheit and Laursen, 2013a),
which is in line with our results (41% for HIIT-15 and 34% for
HIIT-30). The lower ratio for HIIT-30 compared to HIIT-15 in
our study might be explained by the relatively low intensity of
recovery intervals (∼30% PPO), which has been associated with
reduced time >90% VO2max when recovery intervals are >20 s
(Buchheit and Laursen, 2013a). The intensity of the recovery
intervals was lower than what is usually recommended in short
interval sessions, but was the highest intensity the athletes could
practically maintain between work intervals, since the resistance
from the ergometer elastics creates a high effort perception, even
at low workloads. However, the lower intensity in the recovery
intervals was compensated by a slightly higher intensity in the
work intervals (∼115% PPO).
It has been suggested that about 10 min must be spent around
VO2max in order to elicit important cardiovascular adaptations
in endurance athletes (Buchheit and Laursen, 2013a). With
8.1 min and 6.8 min, HIIT-15 and HIIT-30 sessions both come
near this recommendation. Since RPE was not maximal at the
end of the sessions (∼8/10), we can speculate that a third set
could have been performed, which would have brought the time
>90% VO2max around 10–12 min.
In the SIT session, athletes reached 87 ±5% of their VO2max
and maintained 1.7 ±1.3 min >90% VO2max. These results
are in line with a study where trained cyclists performing 6
all-out 30-s sprints, interspersed by 2 min of passive recovery,
reached 90 ±3% VO2max and spent 22 ±21 s (range 0–60 s)
>90% VO2max (Buchheit et al., 2012a). Since time spent >90%
VO2max is inversely related to subjects’ VO2max (Buchheit et al.,
2012a), the slightly higher time spent >90% VO2max in our
study could be due to the generally lower VO2max achieved on
kayaking compared to cycling exercise (Michael et al., 2008).
The highest VO2values were reached during the long
supramaximal interval session (HIIT-60), but athletes only
cumulated 4.1 ±1.7 min >90% VO2max during that session,
which still represents a high percentage of the 6 ×1-min work
intervals. The higher intensity of the session, accelerating VO2
kinetics (Hughson et al., 2000), coupled with the longer effort
duration allowed for a high VO2to be reached from the first effort
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Paquette et al. Muscle Oxygenation During HIIT in Kayakers
FIGURE 4 | Individual muscle oxygenation response to the four interval sessions.
bout. More repetitions would have been needed to accumulate
more time >90% VO2max, but it would likely not be possible
to reach 10 min with this session due to its difficulty. It was
suggested that spending 5–7 min at >90% VO2max would likely
be sufficient for team-sports athletes or for maintenance in
endurance athletes. Therefore, such a session could be planned
for sprint kayakers wishing to develop 500-m specific speed while
maintaining VO2max.
Hence, as pointed out by other authors (Midgley and
McNaughton, 2006; Buchheit and Laursen, 2013a), short
intervals are effective for accumulating training time near
VO2max and would therefore be a good choice when the goal
is to increase VO2max.
HIIT and Peripheral Demand
It has been suggested that repeated fluctuations of muscular O2
consumption during training sessions is necessary for muscular
oxidative capacity adaptations (Daussin et al., 2008a,b), and
that low O2partial pressure at the muscle level is needed
to induce mitochondrial biogenesis (Hoppeler et al., 2003).
Hence, training sessions that elicit repeated high levels of muscle
deoxygenation might present an adequate stimulus to foster
peripheral adaptations. Understanding the degree of muscle
deoxygenation that occurs during training is therefore important,
as it is likely that localized O2availability and extraction
triggers the cascade of signals responsible for the marked
metabolic adaptations witnessed after high-intensity exercise
(Coffey and Hawley, 2007). Muscle deoxygenation during both
effort and rest periods were considered in this study, to obtain a
complete picture of peripheral metabolic disturbances during the
given sessions.
The short interval sessions were the ones eliciting the least
deoxygenation and the lowest time spent at high levels of muscle
deoxygenation. HIIT-60 elicited a higher muscle deoxygenation
than short interval sessions in the VL, but did not elicit a
greater time at high deoxygenation levels. SIT was the most
effective session to elicit both high and sustained levels of muscle
deoxygenation. This is in line with Buchheit et al. (2012a) study,
showing muscle deoxygenation during six 30-s all-out efforts
to be similar to values observed during maximal voluntary leg
contractions or occlusion, known to produce near-to-maximal
muscle desaturation. Our results also suggest that effort bout
intensity is the most important factor determining the time spent
at high levels of muscle deoxygenation. This is in line with results
from Stöcker et al. (2015), where a higher cycling intensity was
associated with greater muscle deoxygenation. The duration of
the work intervals would also have an impact on the degree of
muscle deoxygenation. For example, repeated 4-s sprints would
reduce SmO2by about 12% (Buchheit et al., 2012b), compared
to a reported reduction of 27% for longer sprints (30 s) (Buchheit
et al., 2012a).
NIRS SmO2value represents the balance between O2delivery
and extraction within the muscle (Ferrari et al., 2011). Thus,
a decreased SmO2value could be due to both decreased O2
delivery and/or increased O2extraction by the muscle. In
supramaximal efforts, it is likely that strong muscle contraction
limit O2delivery (Bhambhani, 2004), as suggested by decreased
total hemoglobin concentration during SIT (Jones et al., 2015).
But deoxyhemoglobin concentration also increased during SIT,
suggesting that an increase in muscle O2extraction also occurs
(Jones et al., 2015). We chose to only present SmO2here,
since recent studies have found that the Moxy monitor provides
credible and reliable SmO2values (McManus et al., 2018), but
that total hemoglobin values had low variation during exercise
and were probably not a valid indicator of blood volume (Crum
et al., 2017).
Taken together, these results suggest that SIT elicits a high
muscle O2demand, and while the optimal amount of time spent
at high muscle deoxygenation in training is not known, it appears
that SIT would be an ideal training session to elicit peripheral
adaptations. These findings are in line with previous studies
showing various peripheral adaptations following SIT (Gibala
and McGee, 2008) and a study where muscle deoxygenation
was increased in hockey players during SIT following 6 sessions
of cycling SIT, potentially indicative of an increase muscle O2
extraction capacity with SIT (Jones et al., 2015).
We suggested that HIIT-60 session would represent a good
stimulus to improve peripheral adaptations without requiring
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Paquette et al. Muscle Oxygenation During HIIT in Kayakers
a maximal effort from the athletes. However, we found that
even though maximal deoxygenation was not different from SIT
session, time spent at high deoxygenation levels tended to be
lower compared to SIT. This is explained by the fact that maximal
deoxygenation was only reached near the end of the 1-min work
intervals at 130% PPO. We could hypothesize that increasing the
intensity during the first 10–15 s of the HIIT-60 work intervals
could induce a faster deoxygenation and potentially higher time
spent near maximal deoxygenation. Also, HIIT-60 allowed for
greater time spent at high deoxygenation level compared to
sessions HIIT-15 and HIIT-30 only for the VL, and therefore
would be a good hybrid between high central demand and high
peripheral demand sessions only for this muscle.
Upper-body muscles deoxygenated to a greater extent in
short interval sessions compared to the lower-body muscle
investigated. These differences between muscle groups may be
explained by a difference in contribution of these muscles.
It is possible that upper-body muscles contribute more
compared to lower-body muscles to the effort; however, this
difference seems to dissipate at higher intensities (>130%
PPO). This difference may also come from the lower oxidative
capacity of upper body motor units compared to leg muscles
(Bhambhani et al., 1998).
We hypothesized that SIT would be an optimal stimulus
for peripheral adaptations, but that it would be associated with
a higher effort perception. However, while RPE rating was
higher following the SIT session compared to the other HIIT
sessions, the difference did not reach statistical significance
(p=0.08). Session enjoyment was thus similar in all 4 HIIT
sessions, suggesting athletes’ compliance would not be an issue
for any of these sessions (Scanlan et al., 1993). More research
is needed to understand the effect of HIIT type on fatigue
and recovery.
Even though interval sessions were not matched for interval
duration (effort duration varied from 180 to 600 s between
sessions), central and peripheral responses were compared
between sessions using absolute time-derived variables. Indeed,
training sessions were not matched by duration or energy
expenditure, but by effort, which is how coaches prescribe
training sessions in the field. So if physiological adaptations
are driven by the time spent in a given acute physiological
state, we believe using typical training sessions and looking at
absolute time-derived variables is the best approach in an applied
sport research context. Mixing canoeing and kayaking in this
study is a potential limitation, given that muscle activity differs
between disciplines.
Practical Applications
The present study highlights the different acute physiological
responses to various types of HIIT. Coaches and athletes
who wish to improve VO2max through central adaptations
should include short intervals to their program. In canoe-kayak,
and likely in other upper-body dominant sports, peripheral
adaptations are associated with performance and, therefore, SIT
sessions targeting the muscle oxidative adaptations should also be
included in the training program. Longer supramaximal intervals
could be used to train race specific speed while still stimulating
VO2max, but should probably be modified in order to really
target peripheral adaptations.
CONCLUSIONS
Time spent near VO2max is high during short-interval HIIT
sessions performed on a canoe or kayak ergometer. However,
all-out 30-s sprints are required to elicit high and sustained
levels of muscle deoxygenation. These findings regarding the
acute physiological changes associated with different types
of HIIT give insights on potential physiological adaptations
following different HIIT protocols. Future studies should assess
the chronic effect of HIIT and SIT sessions to ascertain
whether time spent near VO2max and time spent near maximal
muscle deoxygenation are important determinants of VO2max
and maximal deoxygenation adaptations, respectively, and
performance in canoe-kayak athletes.
DATA AVAILABILITY
The datasets generated for this study are available on request to
the corresponding author.
ETHICS STATEMENT
This study was carried out in accordance with the
recommendations of Ethics Committee for Health Sciences
research of Laval University with written informed consent
from all subjects. All subjects gave written informed consent in
accordance with the Declaration of Helsinki. The protocol was
approved by the Ethics Committee for Health Sciences research
of Laval University.
AUTHOR CONTRIBUTIONS
All authors listed have made a substantial, direct and intellectual
contribution to the work, and approved it for publication.
FUNDING
This research received fundings from the Institut National
du Sport du Québec, including funds for open access
publication fees.
ACKNOWLEDGMENTS
Preliminary results from this study were presented at the
European College of Sport Science hosted in Dublin, Ireland
in 2018 (MP, FB, FB muscle oxygenation response to high-
intensity interval training in sprint canoe-kayak. 23rd annual
Congress of the European College of Sport Science, Dublin,
Ireland, 2018).
Frontiers in Sports and Active Living | www.frontiersin.org 8July 2019 | Volume 1 | Article 6

Paquette et al. Muscle Oxygenation During HIIT in Kayakers
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Conflict of Interest Statement: The authors declare that the research was
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