Effects of Including Sprints in One Weekly Low-Intensity Training Session During the Transition Period of Elite Cyclists

Abstract

The purpose of this study was to investigate the effects of including 30-s sprints in one weekly low-intensity training (LIT) session during a 3-wk transition period in elite cyclists. Sixteen male elite cyclists (maximal oxygen uptake, VO2max: 72±5 mL·kg-1·min-1) reduced their training load by ~60% for 3 wks from the end of competitive season and performed only LIT (CON) or included 30-s sprints in one weekly LIT-session (SPR). Performance and physiological capacities were evaluated during a prolonged (~2.5 hrs) test-session, including a strength test, a submaximal blood lactate profile test, an incremental test to exhaustion to determine VO2max, 1 h continuous cycling including 4 maximal 30-s sprints, and a 20-min all-out test. In addition, mental recovery was evaluated using the Athlete Burnout Questionnaire. The only significant between-group change during the transition period was an 8±11% larger improvement in 30-s sprint performance in SPR compared to CON (SPR: 4±5%, CON: -4±5%, p= .01). Although not different from CON, SPR maintained 20-min all-out performance (-1±5%, p= .37) and fractional utilization of VO2max (1.9±6.1 %-points, p= .18) during the 20-min all-out test, whereas corresponding declines were observed in CON (-3±5%, p= .04, and -2.5±2.9 %-points, p= .02, respectively). Power output at 4 mmol·L-1 blood lactate concentration decreased similarly in SPR (-4±4%, p= .02) and CON (-5±5%, p= .01), while VO2max, maximal aerobic power (Wmax), and total burnout score were unaffected in both groups. Including sprints in one weekly LIT-session in the transition period improves sprint performance and maintains 20-min all-out power and fractional utilization of VO2max without compromising mental recovery. Inclusion of sprints in LIT-sessions may therefore be a plausible, time-efficient strategy during short periods of reduced training.

Full text

Frontiers in Physiology | www.frontiersin.org 1 September 2020 | Volume 11 | Article 1000
ORIGINAL RESEARCH
published: 11 September 2020
doi: 10.3389/fphys.2020.01000
Edited by:
François Billaut,
Laval University, Canada
Reviewed by:
Sarah J. Willis,
University of Lausanne, Switzerland
Tom J. Hazell,
Wilfrid Laurier University, Canada
*Correspondence:
Nicki Wineld Almquist
nicki.almquist@inn.no;
nickiwalmquist@gmail.com
Specialty section:
This article was submitted to
Exercise Physiology,
a section of the journal
Frontiers in Physiology
Received: 01 June 2020
Accepted: 23 July 2020
Published: 11 September 2020
Citation:
Almquist NW, Løvlien I, Byrkjedal PT,
Spencer M, Kristoffersen M,
Skovereng K, Sandbakk Ø and
Rønnestad BR (2020) Effects of
Including Sprints in One Weekly
Low-Intensity Training Session During
the Transition Period of Elite Cyclists.
Front. Physiol. 11:1000.
doi: 10.3389/fphys.2020.01000
Effects of Including Sprints in One
Weekly Low-Intensity Training
Session During the Transition Period
of Elite Cyclists
NickiWineldAlmquist1,2*, IneLøvlien1, PerThomasByrkjedal3, MattSpencer3,
MortenKristoffersen4, KnutSkovereng2, ØyvindSandbakk2 and BentR.Rønnestad1
1 Section for Health and Exercise Physiology, Inland Norway University of Applied Sciences, Lillehammer, Norway,
2 Centre for Elite Sports Research, Department of Neuromedicine and Movement Science, Norwegian University of Science
and Technology, Trondheim, Norway, 3 Department of Sport Science and Physical Education, University of Agder,
Kristiansand, Norway, 4 Department of Sport, Food and Natural Sciences, Western Norway University of Applied Sciences,
Bergen, Norway
The purpose of this study was to investigate the effects of including 30-s sprints in one
weekly low-intensity training (LIT) session during a 3-week transition period in elite cyclists.
Sixteen male elite cyclists (maximal oxygen uptake, VO2max: 72±5ml·kg−1·min−1) reduced
their training load by ~60% for 3weeks from the end of competitive season and performed
only LIT or included 30-s sprints (SPR) in one weekly LIT-session. Performance and
physiological capacities were evaluated during a prolonged (~2.5h) test-session, including
a strength test, a submaximal blood lactate prole test, an incremental test to exhaustion
to determine VO2max, 1h continuous cycling including four maximal 30-s sprints, and a
20-min all-out test. In addition, mental recovery was evaluated using the Athlete Burnout
Questionnaire (ARQ). The only signicant between-group change during the transition
period was an 8±11% larger improvement in 30-s sprint performance in SPR compared
to control (CON; SPR: 4±5%, CON: −4±5%, p =0.01). Although not different from
CON, SPR maintained 20-min all-out performance (−1± 5%, p=0.37) and fractional
utilization of VO2max (1.9±6.1%-points, p=0.18) during the 20-min all-out test, whereas
corresponding declines were observed in CON (−3±5%, p=0.04, and −2.5±2.9%-
points, p=0.02, respectively). Power output at 4mmol·L−1 blood lactate concentration
decreased similarly in SPR (−4± 4%, p=0.02) and CON (−5± 5%, p=0.01), while
VO2max, maximal aerobic power (Wmax), and total burnout score were unaffected in both
groups. Including sprints in one weekly LIT-session in the transition period improves sprint
performance and maintains 20-min all-out power and fractional utilization of VO2max without
compromising mental recovery. Inclusion of sprints in LIT-sessions may therefore bea
plausible, time-efcient strategy during short periods of reduced training.
Keywords: periodization strategies, off-season, sprint training, elite athletes, athlete burnout questionnaire

Almquist et al. Including Sprints in Transition Period
Frontiers in Physiology | www.frontiersin.org 2 September 2020 | Volume 11 | Article 1000
INTRODUCTION
e annual training season for an elite cyclist can be broken
into three distinct periods, the preparatory, competition, and
transition period (Mujika et al., 2018). Elite cyclists typically
spend up to 100days in competition (Lucia etal., 2001), which
is both a high physical and psychological exertion, with an
inherent risk of burnout toward the end of the season (Silva,
1990; Lemyre etal., 2006). Although the need for a subsequent
period of physical and mental recovery is regarded as necessary
for elite athletes (Mujika et al., 2018), the manipulation of
training in these transition periods is scarcely investigated
(Garcia-Pallares etal., 2009; Ronnestad et al., 2014). To recover
from the strenuous competition period, cyclists’ training load
is oen drastically reduced for 2–3 weeks in the subsequent
transition period (Lucia etal., 2000; Sassi etal., 2008). However,
too long periods (>4 weeks) of training cessation might lead
to deterioration of performance (Mujika and Padilla, 2000;
Decroix et al., 2016; Maldonado-Martin et al., 2017).
Maintaining a minimum of training load in periods of
decreased training volume seems necessary to avoid performance
decrements (Mujika, 1998; Bosquet et al., 2007), with high-
intensity training (HIT) playing a key role for maintenance
of endurance performance (Neufer, 1989; Garcia-Pallares et al.,
2009; Ronnestad et al., 2014). Maintenance of tness in the
transition period might also be crucial for continuous
improvement in the following seasons of elite athletes (Mujika
et al., 1995). Indeed, a study by Ronnestad et al. (2014) on
well-trained cyclists showed that performing a HIT session
every 7–10 days during an 8-week period following the
competition period maintained power output at 4 mmol·L−1
[BLa−], maximal oxygen uptake (VO2max), and 40-min all-out
performance better than low-intensity training (LIT; Ronnestad
et al., 2014). However, performing HIT-sessions during the
transition period where physical and mental recovery is needed
might be too strenuous, leading to overreaching and burnout.
erefore, including sprint (SPR) training instead might be a
benecial, low-load alternative for elite cyclists.
Short maximal-eort intervals have been reported to be of
less strain compared to longer HIT-intervals (Valstad et al.,
2018) and might serve as an intensive stimulus, sucient for
maintaining endurance performance in shorter periods of reduced
training volume. For example, the addition of sprint training
in periods with 25–65% reductions in training volume has shown
to maintain endurance performance-determining factors in
moderately trained athletes (VO2max, muscle oxidative capacity,
and capillarization; Joyner and Coyle, 2008) and improved
performance at or above intensities eliciting VO2max (Bangsbo
etal., 2009; Iaia etal., 2009; Skovgaard etal., 2018). Furthermore,
including 30-s sprints every 10 min in 60-min LIT-sessions
during an 8-week intervention has recently shown improved
performance in trained cyclists (Gunnarsson etal., 2019). erefore,
implementing 30-s sprints in habitual LIT-sessions for short
transition periods (3 weeks) might be a time-ecient strategy
of relatively low strain for maintaining endurance performance.
erefore, the main aim of this study was to investigate
the eect of including 30-s sprints in one weekly LIT-session
during a 3-week transition period on measures of sprint and
endurance performance in elite cyclists, as well as the associated
changes in physiological capacities and mental recovery.
Wehypothesized that inclusion of sprints during the transition
period would improve sprint performance and maintain
endurance performance-related measures compared to LIT only.
MATERIALS AND METHODS
Participants and Ethics Statement
Twenty-one cyclists volunteered for the study. Two participants
withdrew due to circumstances unrelated to the study and
three participants were excluded due to sickness or lack of
adherence to the intervention, leaving a total of 16 participants.
Physiological parameters, participants’ characteristics, and training
volume are presented in Ta bl e  1. All participants were informed
of the possible risks and discomforts associated with the study
and all gave their written informed consent to participate before
commencing the study. e study was approved by the Local
Ethical Committee at Inland Norway University of Applied
Sciences and performed according to the Declaration of Helsinki,
1975. e study was a multi-center study conducted at four
Norwegian universities with identical laboratory equipment
using the same standardized testing procedures supervised by
the same physician. To categorize the cyclists, the physiological
characteristics suggested by De Pauw et al. (2013) was used.
TABLE1 | Participants’ characteristics measured 3–5days after each cyclists’ last competition and weekly training volume in the last 4weeks of the competition
period.
SPR n=7 CON n=9 Group diff.
Age (years) 22.9±3.0 21.1±3.9 p=0.32
Body mass (kg) 73.6±9.0 73.1±4.8 p=0.89
VO2max (L·min−1) 5.4±0.7 5.2±0.5 p=0.57
VO2max (ml·kg−1·min−1) 73.4±4.9 71.3±4.5 p=0.40
Wmax (W) 439±58 442±48 p=0.93
Power output at 4mmol·L−1 [BLa−] (W) 328±66 321±41 p=0.80
Training volume 30days prior to inclusion (h·wk.−1) 14±4 12±3 p=0.33
Reduction in iTRIMP training load (%) −62±9 −64±11 p=0.72
VO2max, maximal oxygen uptake; Wmax, maximal minute power output (W), reduction in training load per week from 4week of competition period to 3week of transition period
quantied using individualized TRIMP, mean±SD and matching of groups.

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Eleven participants were regarded as performance level 5 athletes
(VO2max: >71 ml·kg−1·min−1, Wmax: >5.5 W·kg−1) and ve
participants were regarded as level 4 athletes (VO2max:
65–71 ml·kg−1·min−1, Wmax: 4.9–6.4 W·kg−1), hence referred to
as elite cyclists.
Experimental Design
e intervention was initiated 3–5 days aer each cyclist’s last
competition of the season and was carried out over
21.2 ± 0.4 days. e participants were randomly assigned to
either a SPR group or a control (CON) group. During the 4
weeks prior to the intervention, the cyclists performed on average
the same number of training sessions per week (SPR: 6.4 ± 0.7
vs. CON: 6.2 ± 1.1 sessions, p = 0.80) of which an equal
amount was characterized as HIT-sessions (SPR: 15 ± 10% vs.
CON: 15 ± 9%, p = 0.95) and the training load from HIT
was not dierent between groups (p = 0.24). SPR and CON
reduced training load from the competition period to the
transition period equally (Tab l e 1 ), and only LIT was performed
during the intervention (SPR: 13± 4 vs. CON: 12± 3 sessions,
p =0.58). However, once a week SPR performed a supervised
90-min LIT-session, riding at a power output equivalent to
60% of VO2max, including three sets of 3×30-s maximal sprints,
interspersed by 4-min of active recovery (100 W) and 15 min
between sets. CON performed a time-matched supervised session
at a power output equivalent to 60% of VO2max.
Testing Procedures
e participants were instructed to refrain from caeine, beta-
alanine, and bicarbonate 24 h prior to testing. Participants
were also instructed to register and duplicate food intake and
time of consumption 24h prior to both tests, but food diaries
were not collected. All testing was performed on the same
time of the day (±1h) in a controlled environmental condition
(16–18°C and 20–35% relative humidity) with a fan ensuring
air circulation around the rider. A schematic presentation of
the prolonged test protocol is outlined in Figure 1.
Strength Test
Aer a 10-min cycling warm-up at self-selected power output
(150–200 W) a predetermined, standardized, 10-repetition
incremental leg press test set to 250 kg for all participants
on a Keiser AIR300 horizontal leg-press dynamometer (Keiser
Sport health equipment INC., Fresno, CA) was initiated.
Changes in strength parameters might aect the sprint ability
and was therefore included (Ronnestad et al., 2017). e
Keiser AIR300 uses pneumatic resistance to measure force
and velocity in each repetition. e incremental test was
performed in the seated position with a 90° knee-joint angle,
starting at 41 kg and increasing to 250 kg at the tenth
repetition with increased and standardized increments and
rest-periods between repetitions. If the participant exceeded
250 kg, the test continued with 60-s rest between attempts
until failure. e participants were instructed to push as
explosively as possible until failure. e theoretical, maximal
velocity (Vmax), maximal force (Fmax), and maximal power
(Pmax) was then calculated based on the second-order polynomial
relationship between force and power (Colyer et al., 2018).
Blood Lactate Prole
Aer a 5-min break, a blood lactate [BLa−] prole test to
determine the relationship between power output, and [BLa−]
concentration during a submaximal continuous incremental
test was initiated. is test has previously been described in
detail (Ronnestad et al., 2010). Briey, participants cycled for
5 min at 175 W, followed by 50-W increments every 5 min
until a [BLa−] of 3 mmol·L−1, aer which increments were
25W. e test was terminated at a [BLa−] of 4mmol·L−1 or higher.
FIGURE1 | Schematic illustration of the test protocol, including strength test, blood lactate [BLa−] prole, 6-s all-out sprint, incremental test to exhaustion, and
60min continuous cycling including 4×30-s maximal sprints and 20-min all-out.

Almquist et al. Including Sprints in Transition Period
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All cycling tests were performed on an electromagnetic braked
cycle ergometer (Lode Excalibur Sport, Lode B. V., Groningen,
e Netherlands), which was adjusted to each cyclists’ individual
preferences and replicated throughout all testing. e xed
modus was used during continuous cycling, allowing the
cyclists to freely choose frequency with a xed resistance.
VO2 measurements started from 2 min into every bout and
VO2 was calculated as an average from 2.5 to 4.5 min. VO2
was measured using a computerized metabolic system with
mixing chamber (Oxycon Pro, Erich Jaeger, Hoechberg,
Germany), which was calibrated every hour. Blood was sampled
from the ngertip on completion of each 5-min bout and
analyzed for whole blood [BLa−] using a lactate analyzer
(Biosen C line, EKF Diagnostic, Germany). Heart rate (HR)
was recorded at the end of each steady-state increment using
the participants’ own HR-monitor and rate of perceived
exertion (RPE) was recorded according to Borg Scale 6–20.
Based on these measures, the power output at 4 mmol·L−1
[BLa−] was calculated by interpolation and was used as a
submaximal performance measure to compare each participant
from Pre to Post.
6-s All-Out Sprint
Aer 5min of active recovery, a 6-s all-out sprint was performed
in the seated position with a stationary start and a resistance
of 0.8 Nm∙kg−1 body mass. Peak power output was dened
as the highest value achieved during the 6-s all-out with
recordings at 6 Hz.
VO2max Test
Aer an additional 5 min of active recovery at ~150 W, an
incremental test to exhaustion to determine VO2max was initiated
at 200 or 250 W depending on previous individual results.
Power output increased by 25 W every minute until the RPM
decreased below 60min−1 despite audible encouragement from
the test leader. VO2max was calculated as the highest average
of a 1-min moving average using 5-s VO2-measurements and
peak heart rate (HRpeak) was registered. Wmax was calculated
as the mean power output during the last minute of the
incremental test.
60min Continuous Cycling With 4×30-s
Maximal Sprints and Subsequently 20-min
All-Out
Ten minutes aer the incremental test to exhaustion, the
participants proceeded with a 60-min continuous cycling session
at an intensity equivalent to 60% of VO2max, which was calculated
from the [BLa-] prole and VO2max using interpolation. Four
repeated 30-s maximal sprints separated by 4 min active
recovery (100 W) were undertaken between 36–50 min and
the test was concluded by a self-paced 20-min all-out without
rest-periods in between (Figure 1). e chosen intensity of
60% of VO2max corroborates well with reported intensities of
competitions (van Erp and Sanders, 2020), making the repeated
sprints and 20-min all-out competition-relevant performance
measures. At Post, the participants rode at the same power
output as Pre during the 60-min continuous cycling. e start
power output on the 20-min all-out was self-selected at Pre
and power and cadence was self-administered throughout the
Pre and Post tests, however, the participants were blinded to
the average power output. e start power output was replicated
at Post to ensure the same pacing conditions. VO2, HR, RPE,
and [BLa−] were measured during the test, according to
Figure1. During sprints, the resistance was set to 0.8Nm·kg−1
in the Wingate modus and started at 80 RPM. Mean power
output was presented as the 30-s average power output sustained
throughout each maximal 30-s sprint. Fractional utilization
of VO2max during the 20-min all-out was calculated from an
average of respiratory VO2-measurements obtained in the
periods 4–5, 9–10, 14–15, and 19–20min, expressed relatively
to VO2max obtained at the respective time-point.
VO2-measurements started 30-s prior to each period to ensure
steady measures of VO2. Water, energy-drink in standard
mixture according to manufacturer’s description (HIGH-5,
UK), and gels (SIS Isotonic Energy Gel, UK) without caeine
were provided ad libitum aer the incremental test to exhaustion
and throughout the test. All participants but one ingested
energy-drink and gels during the experimental tests. e
amount was recorded and repeated at Post to ensure the
same relative hydration-level. On average, 745±369ml energy-
drink and 44 ± 21 ml gel were consumed at Pre and
811 ± 454 ml (p = 0.37) energy-drink and 38 ± 24 ml gel
(p = 0.17) were consumed at Post.
Gross eciency (GE) was dened as the ratio between the
mechanical power output (PO) and the metabolic power input
(PI) calculated using VO2 measurements and the energetic
equivalent (Peronnet and Massicotte, 1991) PI = VO2 L·s−1 x
(4,840 J·L−1 × RER + 16,890 J·L−1). GE was calculated from
the [BLa-] prole test in the fresh state using the power output
closest to that each participant rode at in the 60-min continuous
cycling test. Equivalently, the GE in the semi-fatigued state
was calculated using the steady-state period before sprinting
(30–35 min) in the 60-min continuous cycling test (Figure1).
e power output was not dierent in fresh and semi-fatigued
state in SPR (fresh: 227 ± 39 vs. semi-fatigued: 225 ± 41 W,
p = 0.71) or CON (fresh: 215 ± 28 W vs. semi-fatigued:
219 ± 30 W, p = 0.35).
Training Load and Administration
Training load was quantied using the individualized training
impulse (iTRIMP) as described elsewhere (Manzi etal., 2009),
by weighing exercise intensity according to an individual’s own
HR vs. [BLa−] relationship, calculated by line of best t from
the lactate prole and VO2max test. iTRIMP uses the weighting
factor yi, which increases exponentially based on the HR vs.
[La−] relationship to weight every HR. An accumulated iTRIMP
score was calculated by the following equation:
iTRIMP arbitrary units AU Dx xy
ratio i
()
()
=
()
minDHR
where ΔHRratio is calculated from (HRwork−HRrest)/(HRmax−
HRrest), and D is time spent exercising. Design and training
load administration is specied in Figure 2.

Almquist et al. Including Sprints in Transition Period
Frontiers in Physiology | www.frontiersin.org 5 September 2020 | Volume 11 | Article 1000
Athlete Burnout Questionnaire
To evaluate mental recovery, the 15-item sport-specic Athlete
Burnout Questionnaire (ABQ) was used (Raedeke and Smith,
2001). Athletes were asked to rate “How oen do you feel
this way?” in 15 dierent statements to evaluate their participation
motives in their sport on a 5-point Likert-scale from 1=almost
never to 5=almost always. e ABQ has three 5-item subscales
assessing three key dimensions of burnout: (1) reduced sense
of accomplishment (e.g., “It seems that no matter what I do,
Idon’t perform as well as Ishould”), (2) emotional and physical
exhaustion (e.g., “I feel so tired from my training that I have
trouble nding energy to do other things”), and (3) devaluation
of sport participation (e.g., “e eort I spend participating
in my sport would be better spent doing other things”). A
total summarized score for the ABQ is achieved by averaging
all three subscale scores. e questionnaires were completed
at Pre and Post.
Statistics
Variables were tested for normal distribution using
Shapiro-Wilk test. Based on a study on amateur road cyclists
performing sprint training (Fortes et al., 2019), power
calculations were made to determine the minimum of
participants to include in the present study to detect changes
in sprint performance. Based on the estimated effect size
(ES) of 0.60in changes in sprint performance when reducing
training load for 3weeks (Fortes etal., 2019) together with
an alpha-level of 0.05, a power of 0.80, and a correlation
between repeated measures of 0.50, the minimum sample
size needed to determine significant differences in sprint
performance was calculated to be eight in each group. A
mixed linear model was applied to compare relative changes
between groups in physiological, performance, and strength
measures with group (and sprint) defined as fixed effects
and corrected using Pre-values as a covariate using the
software SPSS v.25. To compare main effects of time, a
mixed linear model was applied with fixed effects defined
by group, and time and random effects were defined by
subject. Data are presented as mean ± SD. To evaluate the
relationship between percentage changes in 20-min all-out
performance and other performance measures, a stepwise,
multiple linear regression was applied. The percentage changes
in power output at 4mmol·L−1 [BLa−], absolute VO2max, Wmax,
[BLa−], and RPE at the end of 20-min all-out and fractional
utilization during 20-min all-out, 30-s sprint performance,
and GE in the semi-fatigued state were included in the
model. For values expressed in %, the changes were calculated
as percentage-points (%-points) by subtracting Post-values
from Pre-values. All variables included in the final model
had a variance inflation factor between 1.2–1.6 and p<0.05.
Whenever a significant main effect was obtained, a Sidak
post hoc analysis was performed with an alpha-level of 0.05.
Values of p>0.05 and p<0.1 were described as approaching
significance. Hopkins’ ES using pooled SD± 95% confidence
interval (CI) was calculated to highlight the practical
significance of differences in performance changes between
groups. Interpretations of the magnitude of ES were as
follows: <0.2 trivial, 0.2–0.6 small, 0.6–1.2 moderate, 1.2–2.0
large, and 2.0–4.0 very large difference (Hopkins etal., 2009).
RESULTS
Sprint Performance
Aer the 3-week transition period, SPR had a larger increase
in 30-s sprint performance than CON from Pre to
Post (8 ± 11%, p = 0.01) with ES on changes between
groups being moderate to large (ES: 0.6–1.7, Figure 3B).
FIGURE2 | Training load during lead-in and 3week intervention using the individualized TRIMP method. Mean±SD.

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An overall, positive eect of time was observed in 30-s sprint
performance in SPR (p = 0.04) and a negative eect of time
was observed in CON (p=0.01, Figure3A). ES were considered
small to moderate for all Post sprints in SPR (rst sprint:
0.2 ± 0.3, second sprint: 0.4 ± 0.9, third sprint: 0.9 ± 1.1,
fourth sprint: 0.7 ± 0.5) and small to moderate eects for
CON (rst sprint: −0.5± 0.3, second sprint: −0.5 ± 0.2, third
sprint: −0.7 ± 0.3, fourth sprint: −0.5 ± 0.3) in relation to
Pre. Peak power output during 6-s sprint did not change
dierently between groups (p= 0.59, Figure 3B) and did not
change from Pre to Post in either group (Figure 3A).
20-min All-Out
Twenty-minutes all-out performance did not change dierently
between groups (p = 0.63, ES: 0.1, Figure 4C). However,
20-min all-out performance was maintained from Pre to
Post in SPR (−1 ± 5%, p = 0.37, ES: −0.2 ± 0.4), whereas
a small decline of −3±5% was observed in CON (p = 0.04,
ES: −0.4 ± 0.3, Figure 4A). Fractional utilization of VO2max
during 20-min all-out did not change dierently between
groups but the dierence in change was considered moderate
(p = 0.19, ES: 0.8, Figure 4D). Specically, SPR maintained
utilization from Pre to Post (1.9 ± 6.1%-points, p = 0.18,
A
B
FIGURE3 | Peak power output (W·kg−1) on maximal 6-s sprint and mean power output on 4×30-s sprints (A, mean±SD) before (Pre) and after (Post) a 3-week
transition period of reduced training load in elite cyclists, including sprints in a low-intensity training session once a week [sprint group (SPR); n=7] or only
performing low-intensity training [control group (CON); n=8] and individual percentage changes from Pre to Post (B). *indicates main effect of time (p<0.05).
§indicates main effect of group on changes from Pre to Post (p<0.05). Mean±SD.

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ES: 0.2 ± 4.5), whereas CON decreased moderately
(−2.5 ± 2.9%-points, p = 0.02, ES: −0.6 ± 2.3, Figure 4B).
[BLa−] and RPE aer 20-min all-out did not change dierently
between groups (p = 0.54 and p = 0.26, respectively) and
was unaltered from Pre to Post in SPR and CON (Tab l e  2 ).
Likewise, the change in %HRpeak during 20-min all-out was
not dierent between groups (p = 0.18) and was unaltered
from Pre to Post in SPR and CON (Tabl e  2 ). Stepwise
multiple linear regression revealed that changes in fractional
utilization of VO2max during 20-min all-out (p< 0.01), VO2max
(p < 0.01), and GE in the semi-fatigued state (p = 0.05)
explained the changes observed in 20-min all-out (p< 0.01,
adjusted R2 = 0.89).
Performance-Related Measures and Body
Mass
Power output at 4mmol·L−1 [BLa−] decreased similarly from
Pre to Post (p = 0.83, ES: 0.1, Figure 5C) in SPR
(−4 ± 4%, p = 0.02, ES: −0.4 ± 0.2) and CON (−5 ± 5%,
p = 0.01, ES: −0.6 ± 0.4, Figure 5A). Fractional utilization
of VO2max at 4 mmol·L−1 [BLa−] did not change dierently
between groups but the ES was considered moderate (p=0.16,
ES: −1.0, Figure 5D). Specically, SPR maintained fractional
utilization of VO2max at 4 mmol·L−1 [BLa−] (p = 0.69, ES:
0.2 ± 1.1) while CON approached signicance to decrease
moderately (p = 0.09, ES: −1.0 ± 0.7, Figure 5B). GE did
not change dierently between groups from Pre to Post in
fresh (p = 0.18) or semi-fatigued state (p = 0.63; Tab l e  3 ).
e change in GE from fresh to semi-fatigued state was not
dierent between groups at Pre (p=0.13) or Post (p= 0.26);
however, GE decreased from the fresh state to the semi-
fatigued state in SPR at Pre (p = 0.02). e increase in
body mass did not dier between groups from Pre to Post
(p = 0.93, ES: 0.0, Ta b l e  2 ). Specically, body mass tended
to increase in SPR (p = 0.07, ES: 0.1 ± 0.1) and increased
in CON from Pre to Post (p = 0.05, ES: 0.1± 0.1, Ta b l e  2 ).
AB
CD
FIGURE4 | 20-min all-out performance expressed in relative power output (W·kg−1; A) and percentage change (C) from before (Pre) to after (Post) a 3-week
transition period of reduced training load in elite cyclists including sprints in a low-intensity training session once a week (SPR group; n=7) or only performing low-
intensity training (CON group; n=8). Fractional utilization of VO2max during 20-min all-out (%; B) and changes in %-points from Pre to Post (D). *indicates main effect
of time (p<0.05). Mean±SD.

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ere was no dierence in changes between groups in VO2max
or Wmax and both groups remained unchanged from Pre to
Post (Tab l e  2 ).
Strength Parameters
Maximal velocity, Fmax and Pmax, did not change dierently
between groups (p = 0.13 p = 0.65, p = 0.36, respectively)
and Fmax and Pmax, did not change within the group from Pre
to Post (Tab l e  3). However, Vmax was increased by 14 ± 19%
from Pre to Post in CON (p = 0.02).
Burnout Symptoms
Total burnout did not change differently (p=0.49) between
SPR and CON and both groups were unchanged from Pre
to Post. However, for the subscale “reduced sense of
accomplishment,” the difference in development between
groups approached significance (p = 0.09). In the change
from “rarely” toward “sometimes, SPR did not change (Pre:
2.3 ± 0.5 vs. Post: 2.2 ± 0.5, p = 0.62) whereas CON
approached significance” (Pre: 2.5 ± 0.7 vs. Post: 2.8 ± 0.5,
p = 0.04). For “devaluation,” the difference in development
between groups approached significance (p = 0.09) but
neither SPR (Pre: 1.6 ± 0.6 vs. Post: 1.8 ± 0.7, p = 0.26)
nor CON (Pre: 1.7 ± 0.4 vs. Post: 1.5 ± 0.4, p = 0.15)
changed from Pre to Post. No group-differences or within-
group changes were observed for “emotional and
physical exhaustion.”
DISCUSSION
e present study investigated the eects of including 30-s
sprints in a LIT-session once a week during a 3-week transition
period of reduced training load in elite cyclists. e main
nding was that inclusion of sprints in SPR improved sprint
performance compared to LIT only in CON who had a
deterioration hereof. Although no group dierences occurred,
20-min all-out performance and fractional utilization of VO2max
during the 20-min test were maintained in SPR, whereas small
to moderate declines were observed in CON. Power output
at 4 mmol·L−1 [BLa−] was equally reduced in both groups,
while VO2max, Wmax and total burnout were unaected in
both groups.
Sprint Performance
As expected, SPR improved 30-s sprint performance in the
present study, whereas absence of sprinting led to deterioration
of 30-s sprint performance in CON. Although sprint training
has proven to be a potent training modality for both
untrained and trained participants (Gist et al., 2014), this
study is the first to show the potency of improving sprint
performance in elite athletes even by inclusion of a relatively
small amount of sprints (27 × 30-s) during the transition
period. Wealso expected that an improved anaerobic capacity,
indicated by the improved 30-s sprints, should improve
short high-intensity endurance performance, such as Wmax
determined here. However, this was not the case in the
present study, which is in contrast to previous studies where
sprint training is added to the habitual volume of LIT
(Laursen et al., 2002) or when sprints are implemented in
LIT-sessions (Gunnarsson et al., 2019). This discrepancy
could be related to the ~60% decrease in training load,
the relatively short intervention of the present study, compared
to previous studies (3 vs. 7–8weeks) and smaller amounts
of sprint training (27 vs. 96–144 × 30-s sprints; Laursen
et al., 2002; Gunnarsson et al., 2019). In our approach,
neither peak power during 6-s sprint nor Vmax changed
differently between groups but Vmax was improved in CON
only. This is in contrast to previous findings where improved
peak power output (Fortes etal., 2019) and muscle strength
(Martin et al., 1994) were found from short periods
(2–4 weeks) of reduced training volume and maintained
intensity-distribution in well-trained cyclists and runners.
TABLE2 | Changes (Δ) in performance-related measures and body mass from before (Pre) to after (Post) a 3-week transition period of reduced training load in elite
cyclists including sprints in a low-intensity training session once a week [sprint group (SPR); n=7] or only performing low-intensity training [control group (CON); n=9].
Mean±SD.
SPR CON
Pre Post ΔPre Post Δ
[BLa−] 20-min all-out (mmol·L−1) 4.7±3.3 5.6±3.0 0.7±2.2 7.0±2.2 6.2±1.6 −0.7±2.2
RPE 20-min all-out 18.1±2.9 18.1±1.6 0.0±2.8 18.9±0.6 19.3±1.1 0.4±1.4
HR (% of HRpeak) 91.8±4.4 93.4±1.3 1.6±3.8 91.3±0.9 92.3±1.6 1.1±1.6
GE fresh (%) 19.9±1.0 19.5±1.0 −0.4±1.0 19.1±1.0 19.2±1.0 0.1±1.0
GE semi-fatigued (%) 18.9±1.0 18.9±1.0 0.1±1.0 19.1±1.0 19.3±1.0 −0.2±1.1
ΔGE fresh vs. semi-fatigued −1.0±1.2†−0.6±1.1 −0.4±1.2 0.0±1.3 0.0±1.1 0.0±1.2
Body mass (kg) 73.6±9.0 74.2±9.4 0.7±1.0 73.1±4.8 73.7±4.9* 0.8±1.0
VO2max (ml·min−1·kg−1) 73.4±4.9 71.4±4.0 −2.5±5.7 71.3±4.5 71.0±4.8 −0.5±4.0
Wmax (W·kg−1) 6.0±0.3 6.0±0.3 1.1±6.5 6.0±0.5 6.0±0.4 −0.9±4.9
%HRpeak, percent of peak heart rate during 20-min all-out; [BLa−], blood lactate concentration measured 1min after conclusion of 20-min all-out; RPE, rate of perceived exertion
immediately after 20-min all-out; GE, gross efciency measured in steady-state periods in the fresh and the semi-fatigued state during the ~2.5h long test protocol; ΔGE, change in
gross efciency from the fresh state to the semi-fatigued state (%-points); VO2max, maximal oxygen uptake; Wmax, maximal minute power output.
*indicates main effect of time (p<0.05).
†signicant difference between fresh and semi-fatigued state (p<0.05).

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Inactivity has previously been reported to change fiber-type
distribution toward type IIX phenotype (Coyle et al., 1985;
Andersen and Aagaard, 2000). Hypothetically, an absence
of type II muscle fiber activation as might be assumed
during 3 weeks of LIT only and an absence of muscular
activation might therefore favor a switch in fiber-specific
characteristics, toward a more fast-twitch phenotype, possibly
explaining an improved Vmax in CON.
20-min All-Out Performance
Although changes in 20-min all-out performance did not dier
between groups, performance was unaltered in SPR, whereas
a small decline of ~3% was observed in CON. However, the
relevance of avoiding a decrease in 20-min all-out performance
aer prolonged cycling would arguably be of importance in
cycling competitions (van Erp et al., 2019). Endurance
performance, such as 20-min all-out test, is mainly determined
AB
CD
FIGURE5 | Relative power output at 4mmol·L−1 [BLa−] W·kg−1 (A), fractional utilization of VO2max at 4mmol·L−1 [BLa−] (B) and individual changes in
percentage and %-points (C,D) from before (Pre) to after (Post) a 3-week transition period of reduced training load in elite cyclists including sprints in a low-
intensity training session once a week (SPR group; n=7) or only performing low-intensity training (CON group; n=9). *indicates main effect of time (p<0.05).
Mean±SD.
TABLE3 | Strength parameters from before (Pre) to after (Post) a 3-week transition period of reduced training load in elite cyclists including sprints in a low-intensity
training session once a week [sprint group (SPR); n=7] or only performing low-intensity training [control group (CON); n=9].
SPR CON
Pre Post Time Pre Post Time
Vmax (M·S−1) 4.0±0.8 4.1±0.9 p=0.87 3.8±08 4.2±0.5 p=0.02
Fmax (N) 3,030±441 2,971±528 p=0.74 3,400±902 3,095±725 p=0.11
Pmax (W) 1,516±332 1,524±460 p=0.88 1,553±251 1,611±310 p=0.25
Effects of time are dened by p. Mean±SD. Vmax, maximal velocity; Fmax, maximal force; Pmax, maximal power.

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by fractional utilization of VO2max, VO2max, and eciency and
to a lesser fraction anaerobic capacity (Jeukendrup etal., 2000;
Joyner and Coyle, 2008). In the current study, the maintained
20-min performance in SPR was coincided by maintained
fractional utilization of VO2max during the test, whereas it
decreased by ~3%-points in CON. However, VO2max, Wmax, or
GE in fresh state or semi-fatigued state did not change in
any group, and both SPR and CON showed similar decreases
in power output at 4 mmol·L−1 [BLa−]. us, the dierent
development pattern in fractional utilization of VO2max within
groups is probably the main explanation for the changes in
20-min all-out performance. is was further conrmed by
a stepwise multiple linear regression analysis, where changes
in fractional utilization of VO2max during 20-min all-out,
together with changes in VO2max and GE explained 89% of
the variance in 20-min all-out changes, supporting the
importance of these variables for high-intensity endurance
performances (Jeukendrup etal., 2000; Joyner and Coyle, 2008).
e reductions in submaximal exercise measures in CON,
such as fractional utilization of VO2max are possibly related
to a decreased oxidative capacity (Coyle etal., 1984), which
has been reviewed to decline with training reduction in a
volume-dependent fashion (Neufer, 1989). Maintaining or
increasing intensity of exercise during such reduced training
volumes, however, seems of importance to maintain
submaximal endurance performance (Neufer, 1989; Ronnestad
et al., 2014), probably explaining the unchanged fractional
utilizations of VO2max in SPR. is is supported by a previous
study of inclusion of sprint training in a 4-week period of
65% decreased training volume, where mitochondrial oxidative
enzyme activity was maintained (Iaia etal., 2009). Furthermore,
the present study and others (Neufer, 1989; Rietjens et al.,
2001) show that maintaining 30–50% of the training volume
maintains VO2max in trained and elite cyclists for short periods
(3 weeks). e importance of maintaining a minimum of
endurance training is showed in studies where training
cessation decreases VO2max by 7–11% aer 3–5 weeks in
trained athletes (Coyle etal., 1984; Maldonado-Martin etal.,
2017). Changes in blood volume and hemoglobin mass are
regarded as main causes for changes in VO2max (Coyle etal.,
1986), and the unchanged VO2max in the present study is
supported by an unchanged blood volume and hemoglobin
mass, although this measure was only performed on a sub-set
of the participants (see Appendix). However, small decreases
<200 ml in blood volume has recently been shown not to
alter VO2max (Skattebo et al., 2020), which could have been
the case in our short intervention study. Overall, our study
indicates that elite cyclists are able to reduce training load by
~60% for short periods without aecting the maximal
aerobic power.
Mental Recovery
One might expect a decrease in the burnout markers during
the transition period due to the great reduction in training
load and absence of strenuous competitions, which has earlier
been argued a necessity for elite athletes (Mujika et al., 2018).
However, in our study, total burnout was unchanged from
Pre to Post within both groups. e average score for all
subscales were comparable to a recent study in a population
of young elite-sportsmen (Gerber etal., 2018), and the general
low scores in the mental subscales indicates a state of relatively
low burnout in the elite cyclists, possibly explaining why this
does not change during a 3-week transition period. In addition,
only small changes were observed in the subscales, which
indicates that changes in mental recovery might be dicult
to measure during such short periods in a small group of
elite cyclists. In any case, inclusion of sprints in one weekly
LIT-session during the transition period does not seem to
pose any eect on mental recovery compared to LIT only in
elite cyclists with initially low levels of burnout scores.
Limitations
e relatively short intervention applied in the current study
yields limited insight into the eects of including sprints in
LIT-sessions on performance and mental recovery in elite
cyclists. e lack of control of the training and competitions
performed prior to the intervention might aect the outcomes,
despite our eort for matching the groups according to training
load and tness. In addition, food consumption was not strictly
controlled for in the present study and might have introduced
unaccounted noise in the outcomes. However, with the unchanged
body composition (see Appendix) and well-developed nutritional
routines among elite athletes, we regard this possible eect to
besmall. Aer the short transition periods of typically 2–3weeks,
elite cyclists oen increase training load gradually. Whether
the current small, positive eects observed in SPR compared
to CON translate into improved performance later in the
preparatory period and competition period, however, needs
further investigation.
In conclusion, including series of 30-s sprints in a LIT-session
once a week during a 3-week transition period improves sprint
performance compared to LIT only. In addition, 20-min all-out
performance and fractional utilization of VO2max was maintained
in SPR while LIT only reduced these variables. Inclusion of
sprints does not aect the power output at 4mmol·L−1 [BLa−],
which was equally reduced in both groups. However, neither
VO2max and Wmax nor total burnout seem aected by a 3-week
transition period with severely reduced training load independent
of sprinting. Inclusion of sprints in LIT-sessions may therefore
be a plausible, time-ecient strategy to maintain performance
for elite cyclist during short periods of reduced training load
without aecting mental recovery.
DATA AVAILABILITY STATEMENT
e raw data supporting the conclusions of this article will
be made available by the authors, without undue reservation.
ETHICS STATEMENT
e studies involving human participants were reviewed and
approved by Local Ethical Committee at Inland Norway

Almquist et al. Including Sprints in Transition Period
Frontiers in Physiology | www.frontiersin.org 11 September 2020 | Volume 11 | Article 1000
University of Applied Sciences. e patients/participants provided
their written informed consent to participate in this study.
AUTHOR CONTRIBUTIONS
NA, MS, MK, KS, ØS, and BR contributed to conception
and design of the study. NA, IL, PB, MK, and KS executed
the study and collected data. NA performed the statistical
analysis. NA wrote the rst dra of the manuscript. All
authors contributed to manuscript revision, read, and approved
the submitted version.
ACKNOWLEDGMENTS
e authors thank Arnt Erik Tjønna for his brilliant technical
assistance and express their gratitude to the elite cyclists who
dedicated their valuable time in the transition period to this study.
SUPPLEMENTARY MATERIAL
e Supplementary Material for this article can befound online
at: https://www.frontiersin.org/articles/10.3389/fphys.2020.01000/
full#supplementary-material
REFERENCES
Andersen, J. L., and Aagaard, P. (2000). Myosin heavy chain IIX overshoot in
human skeletal muscle. Muscle Nerve 23, 1095–1104. doi: 10.1002/1097-
4598(200007)23:7<1095::AID-MUS13>3.0.CO;2-O
Bangsbo, J., Gunnarsson, T. P., Wendell, J., Nybo, L., and omassen, M. (2009).
Reduced volume and increased training intensity elevate muscle Na+-K+
pump alpha2-subunit expression as well as short- and long-term work
capacity in humans. J. Appl. Physiol. 107, 1771–1780. doi: 10.1152/
japplphysiol.00358.2009
Bosquet, L., Montpetit, J., Arvisais, D., and Mujika, I. (2007). Eects of tapering
on performance: a meta-analysis. Med. Sci. Sports Exerc. 39, 1358–1365.
doi: 10.1249/mss.0b013e31806010e0
Colyer, S. L., Stokes, K. A., Bilzon, J. L. J., Holdcro, D., and Salo, A. I. T.
(2018). Training-related changes in force-power proles: implications for
the skeleton start. Int. J. Sports Phys iol. Perform . 13, 412–419. doi: 10.1123/
ijspp.2017-0110
Coyle, E. F., Hemmert, M. K., and Coggan, A. R. (1986). Eects of detraining
on cardiovascular responses to exercise: role of blood volume. J. Appl. Physiol.
60, 95–99. doi: 10.1152/jappl.1986.60.1.95
Coyle, E. F., Martin, W. H. 3rd, Bloomeld, S. A., Lowry, O. H., and
Holloszy, J. O. (1985). Eects of detraining on responses to submaximal
exercise. J. Appl. Physiol. 59, 853–859. doi: 10.1152/jappl.1985.59.3.853
Coyle, E. F., Martin, W. H. 3rd, Sinacore, D. R., Joyner, M. J., Hagberg, J. M.,
and Holloszy, J. O. (1984). Time course of loss of adaptations aer stopping
prolonged intense endurance training. J. Appl. Physiol. Respir. Environ. Exerc .
Physiol. 57, 1857–1864. doi: 10.1152/jappl.1984.57.6.1857
De Pauw, K., Roelands, B., Cheung, S. S., de Geus, B., Rietjens, G., and
Meeusen, R. (2013). Guidelines to classify subject groups in sport-science
research. Int. J. Spor ts Physiol. Perform. 8, 111–122. doi: 10.1123/ijspp.8.2.111
Decroix, L., Piacentini, M. F., Rietjens, G., and Meeusen, R. (2016). Monitoring
physical and cognitive overload during a training camp in professional female
cyclists. Int. J. Sports Physiol . Perfor m. 11, 933–939. doi: 10.1123/ijspp.2015-0570
Fortes, L. S., Costa, B. D. V., Paes, S. T., Perez, A., and Diefenthaeler, F. (2019).
Eect of during of tapering on anaerobic power and capacity in road cyclists.
Sci. Sports. doi: 10.1016/j.scispo.2019.10.009 (in press).
Garcia-Pallares, J., Sanchez-Medina, L., Carrasco, L., Diaz, A., and Izquierdo, M.
(2009). Endurance and neuromuscular changes in world-class level kayakers
during a periodized training cycle. Eur. J. Appl. Physiol. 106, 629–638. doi:
10.1007/s00421-009-1061-2
Gerber, M., Gustafsson, H., Seelig, H., Kellmann, M., Ludyga, S., Colldge, F.,
et al. (2018). Usefulness of the Athlete Burnout Questionnaire (ABQ) as a
screening tool for the detection of clinically relevant burnout symptoms
among young elite athletes. Psychol. Sport Exerc. 39, 104–113. doi: 10.1016/j.
psychsport.2018.08.005
Gist, N. H., Fedewa, M. V., Dishman, R. K., and Cureton, K. J. (2014). Sprint
interval training eects on aerobic capacity: a systematic review and meta-
analysis. Sports Med. 44, 269–279. doi: 10.1007/s40279-013-0115-0
Gunnarsson, T. P., Brandt, N., Fiorenza, M., Hostrup, M., Pilegaard, H., and
Bangsbo, J. (2019). Inclusion of sprints in moderate intensity continuous
training leads to muscle oxidative adaptations in trained individuals. Phys. Rep.
7:e13976. doi: 10.14814/phy2.13976
Hopkins, W. G., Marshall, S. W., Batterham, A. M., and Hanin, J. (2009).
Progressive statistics for studies in sports medicine and exercise science.
Med. Sci. Sports Exerc. 41, 3–13. doi: 10.1249/MSS.0b013e31818cb278
Iaia, F. M., Hellsten, Y., Nielsen, J. J., Fernstrom, M., Sahlin, K., and Bangsbo, J.
(2009). Four weeks of speed endurance training reduces energy expenditure
during exercise and maintains muscle oxidative capacity despite a reduction
in training volume. J. Appl. Physiol. 106, 73–80. doi: 10.1152/japplphysiol.
90676.2008
Jeukendrup, A. E., Craig, N. P., and Hawley, J. A. (2000). e bioenergetics
of world class cycling. J. Sci. Me d. Sport 3, 414–433. doi: 10.1016/S1440-
2440(00)80008-0
Joyner, M. J., and Coyle, E. F. (2008). Endurance exercise performance: the
physiology of champions. J. Physiol. 586, 35–44. doi: 10.1113/jphysiol.
2007.143834
Laursen, P. B., Shing, C. M., Peake, J. M., Coombes, J. S., and Jenkins, D. G.
(2002). Interval training program optimization in highly trained endurance
cyclists. Med. Sci. Sports Exerc. 34, 1801–1807. doi: 10.1097/00005768-
200211000-00017
Lemyre, P., Treasure, D. C., and Roberts, G. C. (2006). Inuence of variability
in motivation and aect on elite athlete burnout susceptibility. J. Sport
Exe rc. Ps ychol. 28, 32–48. doi: 10.1123/jsep.28.1.32
Lucia, A., Hoyos, J., and Chicharro, J. L. (2001). Physiology of professional
road cycling. Sports Med. 31, 325–337. doi: 10.2165/00007256-200131050-00004
Lucia, A., Hoyos, J., Pardo, J., and Chicharro, J. L. (2000). Metabolic and
neuromuscular adaptations to endurance training in professional cyclists: a
longitudinal study. Jpn. J. Physiol. 50, 381–388. doi: 10.2170/jjphysiol.50.381
Maldonado-Martin, S., Camara, J., James, D. V. B., Fernandez-Lopez, J. R.,
and Artetxe-Gezuraga, X. (2017). Eects of long-term training cessation in
young top-level road cyclists. J. Sports Sci. 35, 1396–1401. doi: 10.1080/02640414.
2016.1215502
Manzi, V., Iellamo, F., Impellizzeri, F., D’Ottavio, S., and Castagna, C. (2009).
Relation between individualized training impulses and performance in distance
runners. Med. Sci. Sports Exerc. 41, 2090–2096. doi: 10.1249/MSS.0b013e3181a6a959
Martin, D. T., Scifres, J. C., Zimmerman, S. D., and Wilkinson, J. G. (1994).
Eects of interval training and a taper on cycling performance and isokinetic
leg strength. Int. J. Sports Med. 15, 485–491. doi: 10.1055/s-2007-1021092
Mujika, I. (1998). e inuence of training characteristics and tapering on the
adaptation in highly trained individuals: a review. Int. J. Sports Med. 19,
439–446. doi: 10.1055/s-2007-971942
Mujika, I., Chatard, J. C., Busso, T., Geyssant, A., Barale, F., and Lacoste, L.
(1995). Eects of training on performance in competitive swimming.
Can. J. Appl. Physiol. 20, 395–406. doi: 10.1139/h95-031
Mujika, I., Halson, S., Burke, L. M., Balague, G., and Farrow, D. (2018). An
integrated, multifactorial approach to periodization for optimal performance
in individual and team sports. Int. J. Sports Phys iol. Perform . 13, 538–561.
doi: 10.1123/ijspp.2018-0093
Mujika, I., and Padilla, S. (2000). Detraining: loss of training-induced physiological
and performance adaptations. Part II: long term insucient training stimulus.
Sports Med. 30, 145–154. doi: 10.2165/00007256-200030030-00001
Neufer, P. D. (1989). e eect of detraining and reduced training on the
physiological adaptations to aerobic exercise training. Sports Med. 8, 302–320.
doi: 10.2165/00007256-198908050-00004

Almquist et al. Including Sprints in Transition Period
Frontiers in Physiology | www.frontiersin.org 12 September 2020 | Volume 11 | Article 1000
Peronnet, F., and Massicotte, D. (1991). Table of nonprotein respiratory quotient:
an update. Can. J. Sport Sci. 16, 23–29.
Raedeke, T. D., and Smith, A. L. (2001). Development and preliminary validation
of an athlete burnout measure. J. Sport Exerc. Psychol. 23, 281–306. doi:
10.1123/jsep.23.4.281
Rietjens, G. J., Keizer, H. A., Kuipers, H., and Saris, W. H. (2001). A reduction
in training volume and intensity for 21 days does not impair performance
in cyclists. Br. J. Sports Med. 35, 431–434. doi: 10.1136/bjsm.35.6.431
Ronnestad, B. R., Askestad, A., and Hansen, J. (2014). HIT maintains performance
during the transition period and improves next season performance in well-
trained cyclists. Eur. J. Appl. P hysiol . 114, 1831–1839. doi: 10.1007/s00421-014-2919-5
Ronnestad, B. R., Hansen, J., and Nygaard, H. (2017). 10 weeks of heavy
strength training improves performance-related measurements in elite cyclists.
J. Sports Sci. 35, 1435–1441. doi: 10.1080/02640414.2016.1215499
Ronnestad, B. R., Hansen, E. A., and Raastad, T. (2010). Eect of heavy strength
training on thigh muscle cross-sectional area, performance determinants,
and performance in well-trained cyclists. Eur. J. Appl. Physiol. 108, 965–975.
doi: 10.1007/s00421-009-1307-z
Sassi, A., Impellizzeri, F. M., Morelli, A., Menaspa, P., and Rampinini, E. (2008).
Seasonal changes in aerobic tness indices in elite cyclists. Appl. Physiol.
Nut r. Metab. 33, 735–742. doi: 10.1139/H08-046
Silva, J. (1990). An analysis of the training stress syndrome in competitive
athletics. J. Appl. Sport Psychol. 2, 5–20. doi: 10.1080/10413209008406417
Skattebo, O., Bjerring, A. W., Aunesen, M., Sarvari, S. I., Cumming, K. T.,
Capelli, C., et al. (2020). Blood volume expansion does not explain the
increase in peak oxygen uptake induced by 10 weeks of endurance training.
Eur. J. Appl. Physiol. 120, 985–999. doi: 10.1007/s00421-020-04336-2
Skovgaard, C., Christiansen, D., Christensen, P. M., Almquist, N. W.,
omassen, M., and Bangsbo, J. (2018). Eect of speed endurance training
and reduced training volume on running economy and single muscle ber
adaptations in trained runners. Phys. Rep. 6:e13601. doi: 10.14814/phy2.13601
Valstad, S. A., von Heimburg, E., Welde, B., and van den Tillaar, R. (2018).
Comparison of long and short high-intensity interval exercise bouts on
running performance, physiological and perceptual responses. Sports Med.
Int. Op en 2, E20–E27. doi: 10.1055/s-0043-124429
van Erp, T., Foster, C., and de Koning, J. J. (2019). Relationship between
various training-load measures in elite cyclists during training, road races,
and time trials. Int. J. Sp ort s Phy siol. Per for m. 14, 493–500. doi: 10.1123/
ijspp.2017-0722
van Erp, T., and Sanders, D. (2020). Demands of professional cycling races:
inuence of race category and result. Eur. J. Sport Sci . 1–12. doi: 10.1080/
17461391.2020.1788651 [Epub ahead of print]
Conflict of Interest: e authors declare that the research was conducted in
the absence of any commercial or nancial relationships that could beconstrued
as a potential conict of interest.
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