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The aim of this study was to determine the effect of time-of-day on sprint swimming performance and on upper and lower body, maximum strength, and muscle power. Twelve well-trained junior swimmers (six male and six female) were tested for bench press (BP) maximum strength and muscle power, jump height countermovement vertical jump (CMJ), crank-arm peak power (10s Wingate test), and time to complete 25 m freestyle at 10:00 am and at 18:00 pm in a random order. Performance was significantly enhanced in the pm compared to the am in 25 m swimming time (1.7%; p = 0.01), BP maximum strength (3.6%, p = 0.04, ES = 1.87), BP muscle power (5.1%, p = 0.00, ES = 2.10), and CMJ height (5.8%; p = 0.02), but not in crank-arm power (4.1%; p = 0.08). Time-of-day increased swimming performance in a magnitude of one-third of the effects observed on upper and lower neuromuscular power, which suggests that factors beyond peak muscle power (i.e. swimming technique) affect 25 m freestyle performance.
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Biological Rhythm Research
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Circadian rhythm effects on
neuromuscular and sprint swimming
Jesús G. Pallarésa, Álvaro López-Samanesa, Jaime Morenoa,
Valentín E. Fernández-Elíasa, Juan Fernando Ortegaa & Ricardo
a Exercise Physiology Laboratory, University of Castilla-La Mancha,
Toledo, Spain.
Accepted author version posted online: 18 Apr 2013.Published
online: 25 Jun 2013.
To cite this article: Jesús G. Pallarés, Álvaro López-Samanes, Jaime Moreno, Valentín E.
Fernández-Elías, Juan Fernando Ortega & Ricardo Mora-Rodríguez (2014) Circadian rhythm effects
on neuromuscular and sprint swimming performance, Biological Rhythm Research, 45:1, 51-60, DOI:
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Downloaded by [HINARI] at 12:39 13 December 2013
Circadian rhythm effects on neuromuscular and sprint swimming
Jesús G. Pallarés, Álvaro López-Samanes, Jaime Moreno, Valentín E. Fernández-Elías,
Juan Fernando Ortega and Ricardo Mora-Rodríguez*
Exercise Physiology Laboratory, University of Castilla-La Mancha, Toledo, Spain
(Received 6 March 2013; nal version received 3 April 2013)
The aim of this study was to determine the effect of time-of-day on sprint swimming
performance and on upper and lower body, maximum strength, and muscle power.
Twelve well-trained junior swimmers (six male and six female) were tested for
bench press (BP) maximum strength and muscle power, jump height countermove-
ment vertical jump (CMJ), crank-arm peak power (10s Wingate test), and time to
complete 25 m freestyle at 10:00 am and at 18:00 pm in a random order. Perfor-
mance was signicantly enhanced in the pm compared to the am in 25 m swimming
time (1.7%; p= 0.01), BP maximum strength (3.6%, p= 0.04, ES = 1.87), BP muscle
power (5.1%, p= 0.00, ES = 2.10), and CMJ height (5.8%; p= 0.02), but not in
crank-arm power (4.1%; p= 0.08). Time-of-day increased swimming performance in
a magnitude of one-third of the effects observed on upper and lower neuromuscular
power, which suggests that factors beyond peak muscle power (i.e. swimming
technique) affect 25 m freestyle performance.
Keywords: time-of-day; chronobiology; bench press; crank-arm Wingate; muscle
power; muscle strength
1. Introduction
During the day, the different aspects of physical performance (i.e. muscle endurance,
muscle power, and cardiorespiratory endurance) oscillate, scoring higher during midday
and early evening, and being depressed during the late night and early morning hours
(Baxter & Reilly 1983; Kline et al. 2007; Souissi et al. 2007; Sedliak et al. 2008;
Souissi et al. 2010; Taylor et al. 2010). Accompanying these diurnal changes of motor
performance, researchers have found changes on basal body temperature and blood
concentration of hormones, which in turn, could affect body uids, muscle metabolism,
and the cardiovascular response to exercise (e.g. heart rate and blood pressure)
(Atkinson & Reilly 1996; Decostre et al. 2005). Other studies, focusing on the effects
of circadian rhythm on the muscle itself, suggest alterations in the actinmyosin cross-
bridging processes (Starkie et al. 1999), phosphagen metabolism, and muscle buffering
capacity (Atkinson & Reilly 1996). Thus, circadian rhythm may have a profound
impact on motor performance through systemic and local muscle mechanisms that are
still open for clarication.
The changes in motor performance associated with circadian rhythm have been
mostly described for long- and medium-term efforts, which depend mainly on
*Corresponding author. Email:
Biological Rhythm Research, 2014
Vol. 45, No. 1, 5160,
Ó2013 Taylor & Francis
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cardiorespiratory endurance (Atkinson et al. 2005; Simmonds et al. 2010). However,
circadian rhythm could also affect short-term competition events that rely on peaks of
muscle strength and power output (Souissi et al. 2007; Teo et al. 2011). For instance,
studies conducted with experienced swimmers have found a close association between
swimming performance and muscle power output, mainly when analyzing the ofcial
short-distance events (i.e. 25 m, 50 m, and 100 m) (Zampagni et al. 2008; Bishop et al.
2009; Potdevin et al. 2011; West et al. 2011). The few studies that have actually exam-
ined the effects of circadian rhythm on swimming performance have found a signicant
reduction from 1.2 to 3.5% in swimming performance when testing 50-m, 100-m, and
200-m freestyle in the early morning (i.e. 6:00 h10:00 h) in comparison to the results
of swimming the same distances in the evening (i.e. 17:00 h22:00 h) (Baxter & Reilly
1983; Deschodt & Arsac 2004; Kline et al. 2007; Martin et al. 2007). However, to our
knowledge, no study has examined the effects of circadian rhythm on the sprint swim-
ming performance (i.e. 25 m).
Based on the published high association between muscle peak power output and
short distance swimming performance (Zampagni et al. 2008; Bishop et al. 2009;
Potdevin et al. 2011; West et al. 2011) and knowing the deleterious effect that perform-
ing in the morning has upon neuromuscular performance (i.e. 3.07.5% reduction)
(Mora-Rodriguez et al. 2012), it is our hypothesis that all-out 25 m swimming perfor-
mance will be affected by circadian rhythm. Moreover, knowing the effects that time-
of-day has on 25 m swimming sprint could be useful to develop strategies that allow
coaches to avoid reduced performance during competition or to optimize the adaptations
during regular training. Therefore, the main aim of this study was to examine the circa-
dian rhythm effects on short-distance swimming performance (i.e. 25 m). A second
objective was to assess if muscle strength and power output of the upper and lower
body were affected similarly by time-of-day and its correlation with 25 m swimming
performance. We hypothesize a parallel decline in 25m swimming performance and
neuromuscular power in the morning, compared with the evening performance.
2. Methods
2.1. Subjects
Twelve well-trained junior swimmers (six male and six female in the age range of 17.1
± 2.7 years) volunteered to participate in this study. The physical and anthropometric
characteristics of the subjects are shown in Table 1. All the participants were experi-
enced swimmers with 8.8 ± 2.6 years of training career. However, none of them had
been involved in a resistance training program for more than six consecutive months
Table 1. Subjectscharacteristics.
All (n= 12) Male (n= 6) Female (n=6)
Age (years) 17.1 ± 2.7 18.3 ± 3.3 15.9 ± 1.5
Height (m) 1.72 ± 0.10 1.81 ± 0.06 1.64 ± 0.04
BM (kg) 65.6 ± 10.2 73.2 ± 7.6 58.0 ± 5.8
BMI (kg m
) 22.0 ± 1.7 22.4 ± 1.2 21.5 ± 2.1
Fat free mass (kg) 30.9 ± 6.8 36.6 ± 4.1 25.1 ± 2.4
Fat mass (%) 16.5 ± 6.8 11.8 ± 4.4 21.1 ± 5.6
Data are presented as mean ± SD.
52 J.G. Pallarés et al.
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per year. Therefore, they were all considered moderately resistance-trained individuals.
The subjects were informed in detail about the experimental procedures and the possible
risks and benets of the project. The study complied with the Declaration of Helsinki
and was approved by the Bioethics Commission of the University of Murcia. Written
informed consent was obtained from each athlete or from their parents or guardians
prior to participation.
2.2. Experimental design
In a random order, participants underwent the same battery of tests in two separated
days at different times of the day: (i) morning (10:00 h) and (ii) evening (18:00 h).
Trials were separated by 36 h in between. The experimental trials were designed to
evaluate the main effects of the time-of-day (morning vs. evening) on swimming and
neuromuscular performance. We selected those times of day for testing (i.e. 10:00 in
the morning and 18:00 in the evening) because they are common competition schedules
for this group of junior competitive swimmers. Participants underwent three familiariza-
tion sessions with the testing techniques and protocols performed in the actual study to
avoid the bias of progressive learning on test reliability. The last familiarization session,
performed in the morning (10:00 a.m.) of the second day prior to the beginning of each
experiment, included the determination of the following variables for each subject
(described later in detail): (i) the individual load (kg) that elicited a 1.00 m s
propulsive velocity (MPV) in the free-weight bench press (BP) exercise and (ii) the
individual load (kg) corresponding to 75% of 1RM in BP exercise (Figure 1).
2.3. Experimental protocol
During the 48 h before testing, subjects refrained from physical activity other than that
required by the experimental trials. The day before the onset of the experiment, height
was measured to the nearest 0.5 cm during a maximal inhalation using a wall-mounted
stadiometer (Seca 202, Seca Ltd., Hamburg, Germany). Upon arrival to the testing facil-
ity, the subjectsbody weights were determined and body fat estimated in a fasted state
using a 4-contact electrode body composition bioimpedance analyzer (Tanita TBF-
300A, Tanita Corp., Tokyo, Japan). After a standardized warm-up that consisted of
5 min of pedaling a stationary bicycle at low intensity and 5 min of static stretches and
joint mobilization exercises, the subjects entered the laboratory to start the neuromuscu-
lar test battery assessments under controlled environmental conditions (i.e. 22 ± 1 °C
and 29 ± 3% relative humidity) and a strict-paced schedule (see Figure 1). These tests
consisted of the measurement of a standard countermovement vertical jump (CMJ)
height and the bar displacement velocity, for loads that elicit maximum muscle strength
(75% of 1 RM) and power output (1 m s
) adaptations in the BP exercise. The neuro-
muscular test battery ended with the assessment of peak muscle power output in a 10 s
crank-arm Wingate test. Finally, all the participants performed a swimming test, cover-
ing a distance of 25 m in freestyle, for which they were timed. The total time session of
each experimental protocol was 70 min.
2.4. Jumping test (CMJ)
Participants were instructed to complete a standard CMJ in which they squatted down
into a self-selected depth at/or below 100° knee exion, prior to explosively performing
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the concentric action. Participants were instructed to keep their hands on their hips at
all times and to maintain the same position at take-off and landing. Flight times were
measured using a vertical jump mat (Optojump, Microgate, Italy). The intraclass
coefcient correlation (ICC) and coefcient of variation (CV) were 0.94 and 3.3%,
respectively. The recorded height for this test was the average of three trials.
2.5. Maximum dynamic strength and maximal muscle power
During the last familiarization session, the individual loads that elicited a bar displace-
ment of 1.00 m s
and the load of 75% of 1RM for BP exercise were identied in a
graded loading test using a linear encoder and its associate software (T-Force System,
Ergotech, Murcia, Spain, 0.25% accuracy). Loads that allow bar displacement at a
velocity of 1.00 m s
are very close to those that maximize the mechanical power out-
put for isoinertial upper body multijoint resistance exercises (e.g. free-weight BP)
(Izquierdo et al. 2002; Sanchez-Medina & Gonzalez-Badillo 2011). In turn, 75% of 1
RM has been described as the minimal load that allows positive adaptations for maxi-
mum strength development in well resistance-trained athletes (American College of
Figure 1. Experimental protocol.
54 J.G. Pallarés et al.
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Sports 2009, Garcia-Pallares et al. 2010). After those loads were individually deter-
mined, changes in bar displacement velocity during the BP exercise as a consequence
of time-of-day (am vs. pm) were measured. Detailed description of the BP and SQ
execution technique, as well as the validity and reliability data of the dynamic measure-
ment system (ICC = 1.00; CV = 0.57%) have recently been reported (Sanchez-Medina &
Gonzalez-Badillo 2011).
2.6. Wingate test
The crank-arm Wingate test was performed on an adjustable, speed dependent arm
ergometer (Monark Cardio Rehab 891E, Varberg, Sweden) tted to the individual sub-
jects dimensions to align the mid-line of the sternum with the bottom bracket. Subjects
warmed up for 5 min with a frictional load of 2.0% of their individual body mass (BM)
using a self-selected cadence. During the warm-up period, two short sprints of 5-s dura-
tion were administered. Then, subjects were requested to crank at 60 rpm without load
(Reiser et al. 2000) at which point, a 5.0% BM resistance was dropped and a timer was
started. At this point subjects cranked as hard and fast as possible for the next 10 s. We
chose a 10-s test duration to avoid the fatiguing effects of performing a 30 s Wingate
test on the subsequent swimming bout. It has been reported that even 45 s Wingate test
is reliable for the measurement of anaerobic power in active university students (Balmer
et al. 2004). After completion of the test, subjects cycled against a light load for as long
as needed for recovery. Subjects were required to remain seated during the entire test.
Crank-arm peak power was identied as the highest cadence (in RPM) times the
frictional resistance in kilopond.
2.7. Swimming test
All participants performed a 25 m swimming test in a 25 m indoor swimming pool.
Swimmers performed a 400-m warm-up swim at 75% of their 400-m competition veloc-
ity, followed by a 5min passive resting period. After the warm-up, the subjects were
instructed to perform one all-out 25 m freestyle swimming test. The swimmers started
in a standardized position in the water, holding the backstroke handle with one hand
and having both feet on the wall. Both trials were held in the lane closest to the wall
(lane 6). Water temperature (27.5 ± 1.0 °C), air temperature (22.4 ± 0.8 °C, relative
humidity (43 ± 3%) and swimming pool lighting were held similar in both trials. All the
starts were on the initiative of the participants. Swim performance was assessed as the
time spent in covering 25 m which was recorded by two independent and experienced
coaches using handheld chronographs able to discriminate up to 1/100 of a second
(Namaste 988, Spain). The average time recording of the two timers was used for
subsequent analyses.
3. Statistical analysis
Data are presented as means and standard deviation (SD). ShapiroWilk test was used
to assess normal distribution of data. Neuromuscular differences between trials (am vs.
pm) were analyzed using one-way analysis of variance for repeated measurements. The
Greenhouse-Geisser adjustment for sphericity was calculated. After a signicant F test,
pairwise differences were identied using the Bonferroni signicance post hoc
procedure. Pearson correlation analysis was used to assess the associations between the
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circadian rhythm declines on neuromuscular tests and 25-m swimming performance.
The signicance level was set at p6.05. Cohens formula for effect size (ES) was used
and the results were based on the following criteria: >0.70 large effect; 0.300.69
moderate effect; 60.30 small effect (Cohen 1988).
4. Results
4.1. Countermovement jump height and velocity against loads for maximum
dynamic strength and muscle power adaptations
The CMJ height was signicantly higher during the evening session (pm) when com-
pared to the morning (am) (4.3%; p= 0.02; ES = 0.65) (Figure 2(C)). Likewise, velocity
for maximal power (i.e. load that allow 1 m·s
) and maximum strength loads (i.e. load
of 75% 1RM) in BP exercise were signicantly greater in the pm protocol when
compared to the am (5.1%, p= 0.00, ES = 2.10; 3.6%, p= 0.04, ES = 1.87; respectively;
Figure 2(A) and (B)).
4.2. Wingate and swimming test
The crank-arm Wingate peak power recorded in the evening (pm) was 3.2% higher
without reaching signicance (p= 0.08, ES = 0.37) when compared to the morning
values (am) (Figure 2(D)). The time spent to cover 25 m freestyle swimming was
Figure 2. Time-of-day effects on velocity for (A) maximal power and (B) maximum strength
loads in BP, jump height (C) and crank-arm Wingate peak power output (D). Data are means
± SD.
Signicant differences compared to the am values. p60.05.
56 J.G. Pallarés et al.
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signicantly lower in the pm protocol (13.4 ± 0.3s) compared to the am (13.7 ± 0.3s)
(1.8%, p= 0.01, ES = 0.72). Ten out of the 12 swimmers improved their 25 m swimming
times in the pm trial while two of them did not respond to time-of-day effect (Figure 3).
5. Discussion
This study examines the effects of time-of-day on shortest ofcial swimming distance
(i.e. 25 m freestyle) and neuromuscular performance of young well-trained swimmers at
two times of the day that t with their habitual training and competition schedules (i.e.
10 am and 18 pm). The novel nding is that the time to complete one all-out 25 m
freestyle swim was signicantly longer (1.8%; p= 0.01) in the morning trial (10:00 h)
compared to the evening (18:00 h). Likewise, neuromuscular performance of upper (BP)
and lower body (countermovement jump) musculature showed signicant performance
decline in the morning when compared to the evening (3.65.1%). This ndings
corroborate results in endurance-trained and active subjects, where time-of-day effects
on neuromuscular performance were tested using either dynamic isoinertial contraction
(Mora-Rodriguez et al. 2012) or isometric and isokinetic maximal voluntary contrac-
tions (Gauthier et al. 2001; Racinais et al. 2005). However, to our knowledge we are
rst to test in the same group of athletes, the effects of time-of-day in an unspecic
power task that involve a single all-out movement (i.e. BP of counter movement jump)
in a 10-s arm cycling task that is somehow more specic to swimming, and nally in
25 m swimming performance.
Only a few studies have actually examined the time-of-day effects on swimming
performance in well and highly trained athletes (Baxter & Reilly 1983; Deschodt &
Arsac 2004; Kline et al. 2007; Martin et al. 2007). On the distances of 50 m, 100 m,
and 200 m, these authors have reported a maximum time-of-day performance decline of
2.53.6% which is slightly higher than the decline presently found for the 25 m free-
style distance (i.e. 1.7%). The differences in the daily uctuation in motor performance
between studies may be related to the specic time of day chosen to test. We tested
swimmers with 8 h separation between trials (i.e. 10:00 h vs. 18:00 h) while larger
differences in performance have been reported if trials are separated further away.
Baxter and Reilly (1983) used a repeated measures study on well-trained swimmers in
Figure 3. Time-of-day effects on swimming performance. Data are means ± SD.
differences compared to the pm values. p60.05.
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the 100-m distance at 5 different circadian times (i.e. 6:30, 9:00, 13:30, 17:00, and
22:00 h). They detected the largest performance difference (3.5%) between 22:00 h (best
result) and 6:30 h (worst result). Similarly, Kline et al. (2007) in a study designed to
examine the circadian rhythm effects on the 200-m swimming performance addressed 8
different circadian times (i.e. 2:00, 5:00, 8:00, 11:00, 14:00, 17:00, 20:00, and 23:00 h)
and reported the largest performance uctuation (3.4%) between 23:00 and 5:00 h (i.e.
worst performance). Of note in both studies, the performance differences reported
between 10:00 h am and 18:00 h pm is very similar to ours (i.e. 1.02.0%)
To the best of our knowledge we are rst to correlate the effects of time-of-day on
neuromuscular power in the upper and lower body musculature with performance in the
shortest-distance swimming event (i.e. 25 m freestyle). It was our hypothesis that upper
and lower neuromuscular force would be intimately related to performance in this very
short swimming distance (i.e. 25 m). We expected associations much higher than with
longer swimming distances where variables dependent on swimming technique (e.g.
stroke rate and stroke length) are more relevant (Martin et al. 2007). However, we have
found that associations between pm and am on neuromuscular tests and 25 m swimming
performance were not high, and only one correlation approached signicance without
reach it (swimming vs. BP at a load of 1 m s
;r= 0.44; p= 0.08). The magnitude of
the decline in BP maximal movement velocity at 1 m s
in the am was around 5.1%
while swimming performance decreased by only 1.7% which is one third of the decline
in BP performance. Thus, it seems that up to two thirds of the decline in upper body
peak power could be compensated during 25 m freestyle where 1215 complete arm
stroke cycles are executed in around 13 s. The lack of stronger association suggests that
factors like muscle endurance or swimming technique also play an important role in
25 m swimming performance.
The association between the decline in am to pm in swimming time to complete
25 m freestyle and the decline in pm to am in CMJ height (a surrogate of leg power)
was low (i.e. r= 0.12, p= 0.70). Other authors have reported that the CMJ height is
highly correlated with 15-m swimming performance when starting from a block start
(West et al. 2011). In our study, we measure the time-of-day effects in the jumping abil-
ity of swimmers and our results are in line with those reported by Teo et al. (2011) and
Racinais et al. (2004) on college students. However, we found a poor correlation
between the reductions in swimming performance between am and pm and the reduc-
tions in jumping power. This could be due to the fact that our swimmers did not start
from the block but from the water and thus leg extension peak power was probably not
possible to reach due to water resistance. We did not measure time to complete half a
swimming pool lap (12.5 m) and therefore it is possible that a stronger correlation may
have been found with that intermediate time.
Crank-arm peak power also seemed to be under circadian inuence as the other
neuromuscular variables, but the effects did not reach statistical differences. The am
and pm differences (3.7%, p= 0.10) are lower than those described for well-trained
swimmers by Deschodt and Arsac (Deschodt and Arsac 2004) using leg cycling
Wingate test. These authors reported a 7.8% enhancement in peak power during pm in
comparison to am. However, other researchers that have evaluated the circadian rhythm
effects on the lower-body Wingate test on experienced athletes, have reported differ-
ences similar to ours between am and pm protocols (i.e. 2.55.7%) (Souissi et al. 2010;
Chtourou et al. 2011). We contend that our data on crank- arm peak power is more spe-
cic to swimming than leg cycling peak power and thus more applicable to swimming.
However, we recognize that more studies with a larger number of subjects are needed
58 J.G. Pallarés et al.
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to discard or accept an association between crank-arm cycling and swimming
In conclusion, time-of-day signicantly affects 25 m freestyle swimming perfor-
mance in conjunction with neuromuscular peak performance (i.e. power or maximal
force in the upper and lower body musculature) under climate controlled conditions in
junior competitive swimmers with signicant reductions in morning compared to the
evening. Coaches and swimmers should expect an average of 2% reduction in 25 m
freestyle sprint performance in the morning with some swimmers reducing performance
upto 5%, while much fewer having no effect on their performance (18% in our case).
These ndings highlight the need to adequate swimming training schedules of sprinting
swimmers to reduce the morning effects on their performance.
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... All articles other than randomized controlled trials were excluded since their methodological quality could not be assessed. Thus 455 subjects comprised the systematic review [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Table 1 lists all the characteristics of selected studies. ...
... Most of the selected studies were done on male participants (N = 24). Only two studies had both female and male participants [12,21], while there was no information regarding the gender of subjects in three selected studies [11,27,28] (Table 1). ...
... In the majority of studies, subjects underwent the Wingate testing procedure, namely 30 s Wingate testing [7,11,19,23,25,[28][29][30][31][32], 60 s Wingate test [14], 10 s Wingate test [21], and 15 s Wingate test [12]. In some of the selected studies, a repeat sprint ability test was adopted as a testing procedure to determine the effect of diurnal variation on anaerobic capacity [13,17,18,26,27]. ...
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Purpose Circadian rhythm affects maximal short-term performance, and it is an important determinant of the training component. This review aimed to summarise the influence of circadian rhythm on peak and mean power output of muscle, fatigue index, and blood lactate levels. Methods English language articles were searched through the following databases: PubMed, Web of Science, Science Direct, and Google Scholar, and pertinent randomized control trials were scrutinized. Results The search revealed 17,481 articles, and 29 were included in this systematic review based on inclusion and exclusion criteria. Randomized control trials were selected, and the methodological validity of articles was evaluated using the ‘Cochrane risk of bias tool’. Findings suggest that outcome variables muscle peak power output (p < 0.0001, Z = 7.22, I² = 57.42, SMD = − 0.91, 95% confidence interval CI = − 1.16, − 0.67), muscle mean power output (p < 0.0001, Z = 5.66, I² = 83.85, SMD = − 0.75, 95% CI = − 1.01, − 0.49), and fatigue index (p = 0.02, Z = 2.41, I² = 2.49, SMD = − 0.39, 95% CI = − 0.72, − 0.07) were higher in the evening while the level of blood lactate was higher in the morning (p = 0.79, Z = 0.27, I² = 0.73, SMD = − 0.05, 95% CI = − 0.46, − 0.35). Conclusion The results show that diurnal variation affects both peak and mean power output of muscle as well as fatigue index. However, there is no remarkable effect of circadian rhythm on blood lactate level. A major factor attributed to this finding was the variation in the training experience of participants. For an effective training prescription, it is very important to consider the effect of the biological clock on muscle power output since anaerobic exercise performance is discernibly influenced by the time of the day.
... Even if acute sleep loss has been shown to have a marginal impact on overall performance [24], trained weightlifters often perform better in the evening relative to the morning due to intra-daily variation in epinephrine and norepinephrine signaling and underlying recruitment of energy reserves [25.•]. Similar human performance profiles exist for trained short-distance swimmers (< 100 m; [26,27] and tennis players [28]. Furthermore, time-dependent differences with a preference for evening performance can remain stable even after long-haul travel, as noted in skeleton athletes [29]. ...
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Purpose of Review This review discusses the opportunities and challenges of training and competing “around the clock.” Recent Findings This review focuses on three key areas of study to include: (1) diurnal variation in biologically-driven (circadian-dependent) energy utilization required for aerobic and anaerobic endurance; (2) chronotype and its relationship to athletic performance; and (3) leveraging circadian-driven processes to win “around the clock” and the use of fatigue countermeasures when game time does not align with predicted peaks in athletic performance. Summary Thus, a full-scope understanding of circadian-driven substrates and mechanisms can help to optimize performance. All the research presented is thematically based on case studies and actual performance-related issues from professional athletes (quoted throughout the text).
... Two days before the onset of each experimental trial, the participants refrained from exercising, alcohol and caffeine use [25]. Each participant started the three experimental trials at the same time of day to avoid any circadian rhythm interaction [26]. Prior to the exercise, the participants lay down on a stretcher for 10 min to monitor the heart rate variability (HRV), according to previous studies [27]. ...
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Whole-body electromyostimulation (WB-EMS) training is effective in improving training adaptation. However, WB-EMS may have side effects and contraindications that can lead to excessive muscle damage and physiological impairment. This randomized crossover study aimed to analyze the acute effects of WB-EMS on muscle damage, autonomic modulation and performance during a single maximal strength session in physically active participants. Twenty healthy and physically active participants randomly performed three maximal strength training sessions (90% 1RM) consisting of bench presses and squat exercises, with a continuous stimulus, a coordinated stimulus with concentric and eccentric phases, and without WB-EMS. Data showed no significant differences between the trials for muscle damage (blood creatine kinase levels), lactate blood levels and performance after exercise. Likewise, the heart rate, blood oxygen saturation and the rate of perceived exertion were similar during exercise between trials. The heart rate variability analysis also showed a similar autonomic response among the trials. Training with WB-EMS seemed to be safe at the observed time intervals while offering a stimulus similar to regular training in physically active participants, regardless of the delivery of the electrical stimuli. More studies are needed to assess the effectiveness of WB-EMS in improving exercise adaptations during training programs.
... Participants were encouraged to perform each repetition as fast as possible without taking their feet off the ground. To avoid any effect of circadian rhythms on the jumping performance, participants were scheduled at the same time in both experimental conditions [18]. The descriptive characteristics of the priming exercise are shown in Table 1. ...
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This study aimed to identify the effects of same day resistance priming exercise on countermovement jump parameters and subjective readiness, and to identify whether baseline strength level influenced these outcomes. Fourteen participants performed two separate conditions (Priming [2 sets high-load parallel squats with a 20% velocity loss cut-off] and Control) in a randomized, counterbalanced crossover design. Countermovement jump was assessed at pre, post and 6h while readiness was assessed at pre and at 6h only. All countermovement jump force-time metrics were similar between conditions (p>0.05), but different individual responses were noted 6h after priming. Jump height was increased for 4/14, decreased for another 4/14 and maintained for 6/14 participants at 6h. Higher perceived physical performance capability (p<0.001) and activation balance (p=0.005) were observed after priming only. Positive relationships were observed between strength and the percentage change in jump height (r=0.47-0.50; p=0.033-0.042), concentric peak velocity (r=0.48-0.51; p=0.030-0.041) and impulse (r=0.47; p=0.030-0.045) at post and 6h after priming exercise. These findings suggest that velocity-based high-load low-volume priming exercise has potential to positively impact jump performance and subjective readiness later that day in certain individuals. Participant absolute strength level may influence this response but should be confirmed in subsequent studies.
... In humans, resistance and short-duration maximal exercise performance are influenced by diurnal fluctuations in metabolism, observing peak of performance at the evening (i.e., 16:00-20:00 h) compared to morning schedules (i.e., 6:00-10:00 h) (Grgic et al. 2019;Mirizio et al. 2020;Pallares et al. 2014;Zarrouk et al. 2012) and effect that seem to occur locally in skeletal muscle nor affecting neural structures (Sedliak et al. 2008). Nonetheless, active warm-ups with or without music, exposures to warm and humid environments, fasting conditions or prolonged training periods at morning hours seem to minimize these time-of-day differences in muscle force and power production (Mirizio et al. 2020). ...
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This study aimed to determine if time-of-day could influence physical volleyball performance in females and to explore the relationship between chronotype and volleyball-specific performance. Fifteen young female athletes participated in a randomized counterbalanced trial, performing a neuromuscular test battery in the morning (9:00 h) and the evening (19:00 h) that consisted of volleyball standing spike, straight leg raise, dynamic balance, vertical jump, modified agility T-test and isometric handgrip tests. Chronotype was determined by the morningness-eveningness questionnaire. Compared to the morning, an increased performance was found in the standing spike (4.5%, p = .002, ES = 0.59), straight leg raise test (dominant-limb) (6.5%, p = .012, ES = 0.40), dynamic balance (non-dominant-limb) (5.0%, p = .010, ES = 0.57) and modified T-test (2.1%, p = .049, ES = 0.45) performance in the evening; while no statistical differences were reported in vertical jump tests or isometric handgrip strength. Moreover, no associations were found between chronotype and neuromuscular performance (r = −0.368–0.435, p = .052–0.439). Time-of-day affected spike ball velocity, flexibility in the dominant-limb, dynamic balance in the non-dominant-limb and agility tests. However, no association was reported among these improvements and the chronotype. Therefore, although the chronotype may not play critical role in volleyball-specific performance, evening training/matches schedules could benefit performance in semi-professional female volleyball players
... Three different randomized conditions were implemented throughout the study: a control condition (CON), where no exercise was performed nor caffeine ingested, and two priming exercise conditions. To avoid any effect of circadian rhythms on the variables analyzed, participants were scheduled at the same time in the three experimental conditions (Pallarés et al., 2013). One of the priming conditions consisted of carrying out the priming exercise without any subsequent caffeine intake (Priming). ...
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Purpose: Morning priming exercise and caffeine intake have been previously suggested as an effective strategy to increase within-day performance and readiness. However, the concurrent effect of both strategies is unknown. The present research aimed to map the within-day time course of recovery and performance of countermovement jump (CMJ) outcomes, kinetics, and strategy and readiness after priming alone and in combination with caffeine. Methods: Eleven participants performed a control, a priming exercise (Priming) and a priming with concurrent caffeine intake (PrimingCaf) in a double-blind randomized, crossover design. CMJ metrics were assessed before, post, and 2 h, 4 h, and 6 h after each condition while readiness was assessed at 6 h. Results: Perceived physical, mental performance capability and activation balance were higher at 6 h after Priming and PrimingCaf conditions. Immediate reductions in jump height (5.45 to 6.25%; p < .046), concentric peak velocity (2.40 to 2.59%; p < .041) and reactive strength index-modified (RSImod) (9.06 to 9.23% p < .051) after Priming and PrimingCaf were observed, being recovered at 2 h (p > .99). Concentric impulse was restored in PrimingCaf (p > .754; d = -0.03 to-0.08) despite lower concentric mean force/BM (p < .662; d = -0.18 to -0.26) as concentric duration was increased (p > .513; d = 0.15 to 0.21). Individual analysis revealed that some participants benefit from both strategies as they showed increases in jump height over the smallest worthwhile change while others did not. Conclusions: Psychological readiness was increased after both priming conditions at 6 h; however, it seems necessary to consider individual changes to achieve the positive effects of the priming or the priming in combination with caffeine on jumping outcomes.
... Pavlovic et al., (Pavlović et al., 2018) in support of our findings showed that jump heights followed by static stretching in warm-up were higher at the evening (18:00-19:30 h) compared to morning (08:00-09:30 h) in handball players. In another study used static stretching in warm-up showed that swimmers performed better in CMJ, 25m swimming time, maximal strength, and free weighted bench press in the evening (18:00 h) than morning (10:00 h) (Pallarés et al., 2014). During evening nerve conduction velocity, enzymatic activity, and elasticity of muscles enhance, and muscle viscosity decreases due to increase in body temperature (Behm & Chaouachi, 2011;Bernard, Giacomoni, Gavarry, Seymat, & Falgairette, 1998). ...
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The purpose of the study was to investigate the effect of static stretching on squat jump (SJ) and countermovement jump (CMJ) in diurnal variation. Fifty-three male collegiate athletes (age=21.9±2.6 years; height=179.7±8.1cm; body-mass=75.3±8.6kg; mean±SD) completed the SJ and CMJ tests either after static stretching or no stretching protocols at two times of the day (07:00h and 17:00h) in random order on non-consecutive days. After warming-up for 5 minutes with low-intensity jogging, participants walked for 2 minutes before performing one of the two stretching protocols (static stretching or no stretching) then 4-5 minutes of additional rest was given before SJ and CMJ performances were measured. Jump heights were analyzed using the two-way ANOVA with repeated measures (2[stretching]×2[time-of-day]). No stretching protocol caused better jump heights in both SJ and CMJ (p< .01). SJ heights were higher at 17:00 compared to 07:00 in both static stretching (8.8%) and no stretching (9.1%) protocols (p< .01). Similarly, CMJ heights were higher at 17:00 compared to 07:00 in both static stretching (10.6%) and no stretching (5.8%) protocols (p< .01). Static stretching adversely influenced jump heights both in the morning and evening. However, it caused less negative effect in the evening.
... Die Rolle des Biorhythmus im SchwimmsportDie Erkenntnisse der Studie von FACER-CHILDS und BRANDSTAETTER (2015) lassen sich natürlich eher auf Sportarten außerhalb des Wassers übertragen. Es existieren jedoch auch Studien, die die Auswirkungen des zirkadianen Rhythmus auf die schwimmspezische Leistungsfähigkeit beleuchtet haben(LOK et al. 2020, PALLARÉS et al. 2014, KLINE et al. 2007, ARNETT 2002, MARTIN & THOMPSON 2000, BAXTER & REILLY 1983). LOK et al. (2020) nutzten die Schwimmzeiten der letzten vier olympischen Spiele (von 2004 bis 2016) zur Bestimmung des Einflusses der Tageszeit unter maximalen Motivationsbedingungen. Die Daten derjenigen Athleten, die es bis ins Finale schafften (n=144, 72 Frauen), wurden berücksichtigt und für jeden individuellen Athleten normalisiert, basierend auf den durchschnittlichen Schwimmzeiten über die drei Wettkampftypen (Heats, Semifinals und Finals) für jede Disziplin, jede Distanz und jeden olympischen Austragungsort. ...
Conference Paper
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Erörterung über die Relevanz des Biorhythmus für die sportliche Leistungsfähigkeit (insbesondere im Schwimmsport)
The aim of this study is to examine the daytime effects on flip turn performance [i.e., 3 m round trip time (3mRTT) as measure of turning performance] as well as global performance during a 50 m freestyle at maximal speed. Twelve college swimmers performed 3 × 50 m freestyle at maximum speed with a flip turn and glide in a 25 m pool in two experimental trials, one in the morning (08:00 h) and one in the evening (18:00 h). Kinematic and dynamic parameters of flip turn performance are analyzed using one underwater camera and a force platform recording wall force peak and time contact. Results showed that oral temperature is significantly higher (p < 0.001) in the evening than in the morning. Also, this study reported that daily variations have been observed for both, changes in swim performance and changes in (3mRTT). Thus, kinematic and dynamic flip turn variables associated with an improvement of freestyle swim performance. It is concluded that maximal swimming trials are performed better in the evening than in the morning, and that this might be linked to variations in oral temperature; also, might be explained by better flip turn performance at this time.
Caffeine ingestion can improve performance across a variety of exercise modalities but can also elicit negative side effects in some individuals. Thus, there is a growing interest in the use of caffeine mouth rinse solutions to improve sport and exercise performance while minimizing caffeine’s potentially adverse effects. Mouth rinse protocols involve swilling a solution within the oral cavity for a short time (e.g., 5–10 s) before expectorating it to avoid systemic absorption. This is believed to improve performance via activation of taste receptors and stimulation of the central nervous system. Although reviews of the literature indicate that carbohydrate mouth rinsing can improve exercise performance in some situations, there has been no attempt to systematically review the available literature on caffeine mouth rinsing and its effects on exercise performance. To fill this gap, a systematic literature search of three databases (PubMed, SPORTDiscus, and Web of Science) was conducted by two independent reviewers. The search resulted in 11 randomized crossover studies that were appraised and reviewed. Three studies found significant positive effects of caffeine mouth rinsing on exercise performance, whereas the remaining eight found no improvements or only suggestive benefits. The mixed results may be due to heterogeneity in the methods across studies, interindividual differences in bitter tasting, and differences in the concentrations of caffeine solutions. Future studies should evaluate how manipulating the concentration of caffeine solutions, habitual caffeine intake, and genetic modifiers of bitter taste influence the efficacy of caffeine mouth rinsing as an ergogenic strategy.
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To investigate whether caffeine ingestion counteracts the morning reduction in neuromuscular performance associated with the circadian rhythm pattern. Twelve highly resistance-trained men underwent a battery of neuromuscular tests under three different conditions; i) morning (10:00 a.m.) with caffeine ingestion (i.e., 3 mg kg(-1); AM(CAFF) trial); ii) morning (10:00 a.m.) with placebo ingestion (AM(PLAC) trial); and iii) afternoon (18:00 p.m.) with placebo ingestion (PM(PLAC) trial). A randomized, double-blind, crossover, placebo controlled experimental design was used, with all subjects serving as their own controls. The neuromuscular test battery consisted in the measurement of bar displacement velocity during free-weight full-squat (SQ) and bench press (BP) exercises against loads that elicit maximum strength (75% 1RM load) and muscle power adaptations (1 m s(-1) load). Isometric maximum voluntary contraction (MVC(LEG)) and isometric electrically evoked strength of the right knee (EVOK(LEG)) were measured to identify caffeine's action mechanisms. Steroid hormone levels (serum testosterone, cortisol and growth hormone) were evaluated at the beginning of each trial (PRE). In addition, plasma norepinephrine (NE) and epinephrine were measured PRE and at the end of each trial following a standardized intense (85% 1RM) 6 repetitions bout of SQ (POST). In the PM(PLAC) trial, dynamic muscle strength and power output were significantly enhanced compared with AM(PLAC) treatment (3.0%-7.5%; p≤0.05). During AM(CAFF) trial, muscle strength and power output increased above AM(PLAC) levels (4.6%-5.7%; p≤0.05) except for BP velocity with 1 m s(-1) load (p = 0.06). During AM(CAFF), EVOK(LEG) and NE (a surrogate of maximal muscle sympathetic nerve activation) were increased above AM(PLAC) trial (14.6% and 96.8% respectively; p≤0.05). These results indicate that caffeine ingestion reverses the morning neuromuscular declines in highly resistance-trained men, raising performance to the levels of the afternoon trial. Our electrical stimulation data, along with the NE values, suggest that caffeine increases neuromuscular performance having a direct effect in the muscle.
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The present study was designed to evaluate time-of-day effects on electromyographic (EMG) activity changes during a short-term intense cycling exercise. In a randomized order, 22 male subjects were asked to perform a 30-s Wingate test against a constant braking load of 0.087 kg·kg(-1) body mass during two experimental sessions, which were set up either at 07:00 or 17:00 h. During the test, peak power (P(peak)), mean power (P(mean)), fatigue index (FI; % of decrease in power output throughout the 30 s), and evolution of power output (5-s span) throughout the exercise were analyzed. Surface EMG activity was recorded in both the vastus lateralis and vastus medialis muscles throughout the test and analyzed over a 5-s span. The root mean square (RMS) and mean power frequency (MPF) of EMG were calculated. Neuromuscular efficiency (NME) was estimated from the ratio of power to RMS. Resting core temperature, P(peak), P(mean), and FI were significantly higher (p < .05) in the evening than morning test (e.g., P(peak): 11.6 ± 0.8 vs. 11.9 ± 1 W·kg(-1)). The results showed that power output decreased following two phases. During the first phase (first 20s), power output decreased rapidly and values were higher (p < .05) in the evening than in the morning. During the second phase (last 10s), power decreased slightly and appeared independent of the time of day of testing. This power output decrease was paralleled by evolution of the MPF and NME. During the first phase, NME and MPF were higher (p < .05) in the evening. During the second phase, NME and MPF were independent of time of day. In addition, no significant differences were noticed between 7:00 and 17:00 h for EMG RMS during the whole 30 s. Taken together, these results suggest that peripheral mechanisms (i.e., muscle power and fatigue) are more likely the cause of the diurnal variation of the Wingate-test performance rather than central mechanisms.
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This investigation aimed to quantify the typical variation for kinetic and kinematic variables measured during loaded jump squats. Thirteen professional athletes performed six maximal effort countermovement jumps on four occasions. Testing occurred over 2 d, twice per day (8 AM and 2 PM) separated by 7 d, with the same procedures replicated on each occasion. Jump height, peak power (PP), relative peak power (RPP), mean power (MP), peak velocity (PV), peak force (PF), mean force (MF), and peak rate of force development (RFD) measurements were obtained from a linear optical encoder attached to a 40 kg barbell. A diurnal variation in performance was observed with afternoon values displaying an average increase of 1.5-5.6% for PP, RPP, MP, PV, PF, and MF when compared with morning values (effect sizes ranging from 0.2-0.5). Day to day reliability was estimated by comparing the morning trials (AM reliability) and the afternoon trials (PM reliability). In both AM and PM conditions, all variables except RFD demonstrated coefficients of variations ranging between 0.8-6.2%. However, for a number of variables (RPP, MP, PV and height), AM reliability was substantially better than PM. PF and MF were the only variables to exhibit a coefficient of variation less than the smallest worthwhile change in both conditions. Results suggest that power output and associated variables exhibit a diurnal rhythm, with improved performance in the afternoon. Morning testing may be preferable when practitioners are seeking to conduct regular monitoring of an athlete's performance due to smaller variability.
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This study examined in pubescent swimmers the effects on front crawl performances of a 6-week plyometric training (PT) in addition to the habitual swimming program. Swimmers were assigned to a control group (n = 11, age: 14.1 ± 0.2 years; G(CONT)) and a combined swimming and plyometric group (n = 12, age: 14.3 ± 0.2 years; GSP), both groups swimming 5.5 h · wk(-1) during a 6-week preseason training block. In the GSP, PT consisted of long, lateral high and depth jumps before swimming training 2 times per week. Pre and posttests were performed by jump tests (squat jump [SJ], countermovement jump [CMJ]) and swim tests: a gliding task, 400- and 50-m front crawl with a diving start (V400 and V50, m · s(-1)), and 2 tests with a water start without push-off on the wall (25 m in front crawl and 25 m only with kicks). Results showed improvement only for GSP for jump tests (Δ = 4.67 ± 3.49 cm; Δ = 3.24 ± 3.17 cm; for CMJ and SJ, respectively; p < 0.05) and front crawl tests (Δ = 0.04 ± 0.04 m · s(-1); Δ = 0.04 ± 0.05 m · s(-1); for V50 and V400, respectively; p < 0.05). Significant correlations were found for GSP between improvements in SJ and V50 (R = 0.73, p < 0.05). Results suggested a positive effect of PT on specific swimming tasks such as dive or turn but not in kicking propulsion. Because of the practical setup of the PT and the relevancy of successful starts and turns in swimming performances, it is strongly suggested to incorporate PT in pubescent swimmers' training and control it by jump performances.
SUMMARY In order to stimulate further adaptation toward specific training goals, progressive resistance training (RT) protocols are necessary. The optimal characteristics of strength-specific programs include the use of concentric (CON), eccentric (ECC), and isometric muscle actions and the performance of bilateral and unilateral single- and multiple-joint exercises. In addition, it is recommended that strength programs sequence exercises to optimize the preservation of exercise intensity (large before small muscle group exercises, multiple-joint exercises before single-joint exercises, and higher-intensity before lower-intensity exercises). For novice (untrained individuals with no RT experience or who have not trained for several years) training, it is recommended that loads correspond to a repetition range of an 8-12 repetition maximum (RM). For intermediate (individuals with approximately 6 months of consistent RT experience) to advanced (individuals with years of RT experience) training, it is recommended that individuals use a wider loading range from 1 to 12 RM in a periodized fashion with eventual emphasis on heavy loading (1-6 RM) using 3- to 5-min rest periods between sets performed at a moderate contraction velocity (1-2 s CON; 1-2 s ECC). When training at a specific RM load, it is recommended that 2-10% increase in load be applied when the individual can perform the current workload for one to two repetitions over the desired number. The recommendation for training frequency is 2-3 dIwkj1 for novice training, 3-4 dIwkj1 for intermediate training, and 4-5 dIwkj1 for advanced training. Similar program designs are recom- mended for hypertrophy training with respect to exercise selection and frequency. For loading, it is recommended that loads corresponding to 1-12 RM be used in periodized fashion with emphasis on the 6-12 RM zone using 1- to 2-min rest periods between sets at a moderate velocity. Higher volume, multiple-set programs are recommended for maximizing hypertrophy. Progression in power training entails two general loading strategies: 1) strength training and 2) use of light loads (0-60% of 1 RM for lower body exercises; 30-60% of 1 RM for upper body exercises) performed at a fast contraction velocity with 3-5 min of rest between sets for multiple sets per exercise (three to five sets). It is also recommended that emphasis be placed on multiple-joint exercises especially those involving the total body. For local muscular endurance training, it is recommended that light to moderate loads (40-60% of 1 RM) be performed for high repetitions (915) using short rest periods (G90 s). In the interpretation of this position stand as with prior ones, recommendations should be applied in context and should be contingent upon an individual's target goals, physical capacity, and training
To study the effect of temperature on muscle metabolism during submaximal exercise, six endurance-trained men had one thigh warmed and the other cooled for 40 min prior to exercise using water-perfused cuffs. One cuff was perfused with water at 50-55°C (HL) with the other being perfused with water at 0°C (CL). With the cuffs still in position, subjects performed cycling exercise for 20 min at a work load corresponding to 70% VO2,peak (where VO2,peak is peak pulmonary oxygen uptake) in comfortable ambient conditions (20-22°C). Muscle biopsies were obtained prior to and following exercise and forearm venous blood was collected prior to and throughout the exercise period. Muscle temperature (Tmus) was not different prior to treatment, but treatment resulted in a large difference in pre-exercise Tmus (difference = 6·9 ± 0·9°C; P < 0·01). Although this difference was reduced following exercise, it was nonetheless significant (difference = 0·4 ± 0·1°C; P < 0·05). Intramuscular [ATP] was not affected by either exercise or muscle temperature. [Phosphocreatine] decreased (P < 0·01) and [creatine] increased (P < 0·01) with exercise but were not different when comparing HL with CL. Muscle lactate concentration was not different prior to treatment nor following exercise when comparing HL with CL. Muscle glycogen concentration was not different when comparing the trials before treatment, but the post-exercise value was lower (P < 0·05) in HL compared with CL. Thus, net muscle glycogen use was greater during exercise with heating (208 ± 23 vs. 118 ± 22 mmol kg−1 for HL and CL, respectively; P < 0·05). These data demonstrate that muscle glycogen use is augmented by increases in intramuscular temperature despite no differences in high energy phosphagen metabolism being observed when comparing treatments. This suggests that the increase in carbohydrate utilization occurred as a direct effect of an elevated muscle temperature and was not secondary to allosteric activation of enzymes mediated by a reduced ATP content.
This study aimed to analyze the acute mechanical and metabolic response to resistance exercise protocols (REP) differing in the number of repetitions (R) performed in each set (S) with respect to the maximum predicted number (P). Over 21 exercise sessions separated by 48-72 h, 18 strength-trained males (10 in bench press (BP) and 8 in squat (SQ)) performed 1) a progressive test for one-repetition maximum (1RM) and load-velocity profile determination, 2) tests of maximal number of repetitions to failure (12RM, 10RM, 8RM, 6RM, and 4RM), and 3) 15 REP (S × R[P]: 3 × 6[12], 3 × 8[12], 3 × 10[12], 3 × 12[12], 3 × 6[10], 3 × 8[10], 3 × 10[10], 3 × 4[8], 3 × 6[8], 3 × 8[8], 3 × 3[6], 3 × 4[6], 3 × 6[6], 3 × 2[4], 3 × 4[4]), with 5-min interset rests. Kinematic data were registered by a linear velocity transducer. Blood lactate and ammonia were measured before and after exercise. Mean repetition velocity loss after three sets, loss of velocity pre-post exercise against the 1-m·s load, and countermovement jump height loss (SQ group) were significant for all REP and were highly correlated to each other (r = 0.91-0.97). Velocity loss was significantly greater for BP compared with SQ and strongly correlated to peak postexercise lactate (r = 0.93-0.97) for both SQ and BP. Unlike lactate, ammonia showed a curvilinear response to loss of velocity, only increasing above resting levels when R was at least two repetitions higher than 50% of P. Velocity loss and metabolic stress clearly differs when manipulating the number of repetitions actually performed in each training set. The high correlations found between mechanical (velocity and countermovement jump height losses) and metabolic (lactate, ammonia) measures of fatigue support the validity of using velocity loss to objectively quantify neuromuscular fatigue during resistance training.
The study investigated the effects of circadian rhythm of cortisol (C) and testosterone (T) on maximal force production (Fpeak) and power output (Ppeak). Twenty male university students (mean age = 23.8 ± 3.6 years, height = 177.5 ± 6.4 cm, weight = 78.9 ± 11.2 kg) performed 4 time-of-day testing sessions consisting of countermovement jumps (CMJs), squat jumps (SJ), isometric midthigh pulls (IMTPs), and a 1-repetition maximum (1RM) squat. Saliva samples were collected at 0800, 1200, 1600, and 2000 hours to assess T and C levels on each testing day. Session rate-of-perceived exertion (RPE) scores were collected after each session. The results showed that Fpeak and Ppeak presented a clear circadian rhythm in CMJ and IMTP but not in SJ. One repetition maximum squat did not display a clear circadian rhythm. Session RPE scores collected at 0800 and 2000 hours were significantly (p ≤ 0.05) higher than those obtained at 1200 and 1600 hours. Salivary T and C displayed a clear circadian rhythm with highest values at 0800 hours and lowest at 2000 hours; however, no significant correlation was found between T and C with Fpeak and Ppeak. A very strong correlation was found between Taural with Fpeak of CMJ and IMTP and Ppeak of CMJ (r = 0.86, r = 0.84 and r = 0.8, p ≤ 0.001). The study showed the existence of a circadian rhythm in Fpeak and Ppeak in CMJ and IMTP. The evidence suggests that strength and power training or testing should be scheduled later during the day. The use of Taural seemed to be a more effective indicator of physical performance than hormonal measures, and the use of session RPE should also be closely monitored because it may present a circadian rhythm.