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Abstract

BACKGROUND:

The circadian rhythm (CR) is a 24-hour cyclic period that influences a wide array of physiological systems and performance sports. However, its specific effect on drop jump (DJ) scores have not been studied.

OBJECTIVE:

To investigate the effect of circadian rhythm on DJ performances.

METHODS:

Thirty-three healthy university students (men, $n=$ 16, age: 23.47 $\pm$ 2.9 years; fewomen, $n=$ 17, age: 22.25 $\pm$ 2.27 years) participated in this study. Subjects were tested twice, over two separate days, once in the morning and once in the evening. Subjects started from a drop height of 20 cm and continued until the height where the reactive strength index (RSI) started to decrease. This height was recorded as the optimal drop height (ODH). Ground contact time (GCT) and jump height were also recorded.

RESULTS:

The ODH values were similar between testing sessions for both genders ( $p>$ 0.05). A significant increase in jump height during the evening session was observed in men ( $p=$ 0.005, $d=$ 0.80). The RSI values increased significantly in men ( $p=$ 0.006, $\eta$ 2 $=$ 0.77) while GCT was similar in both genders ( $p>$ 0.05).

CONCLUSION:

In men, the optimal time of day for DJ explosive training is the evening. Women may benefit from this type of training both during morning and evening sessions.

Keywords

Circadian rhythm drop jump reactive strength index optimal drop height jump height ground contact time

1. Introduction

A stretch-shortening cycle (SSC) is described as a combination of muscle lengthening (eccentric) immediately followed by a shortening (concentric) contraction [1]. One of the common methods for measuring the SSC level is the drop jump (DJ). During a DJ, participants drop from a height and perform an explosive vertical jump following the landing. A short duration of ground contact time (GCT) and a higher jump performance is expected to determine the SSC level. This determination is carried out with the reactive strength index (RSI) [2] (flight time/contact time), which is an indicator of the optimal drop height (ODH) [3].

The monitoring of athletic performance has gained importance for practitioners, especially to prevent injuries among athletes [4, 5, 6]. The other purpose of such monitoring is to determine the optimal load of training for each athlete to reach higher performance [6]. The main goal of the present study was to determine the best monitoring time of day for SSC by using the DJ test. Many other athletic performance markers, such as anaerobic power or aerobic performances, are influenced by the time of day at testing, as described below.

The circadian rhythm (CR) is a 24-hour cyclic period that influences a wide array of physiological systems [7]. CR can be explained by several mechanisms such as environmental and internal changes in the biological clock. CR is also important in performance sports. It is stated that coaches should take into account the influence of the time of day and chronotype effects while planning training sessions [8]. Studies have taken different approaches to investigating how CR influences athletic performance [9]. The effect of diurnal variations on physical performance in various aerobic and anaerobic activities have been studied for some time. For example, in a study by Ryan et al. [10], it was stated that significant differences were seen in distances covered and high-speed running distances during Australian rules football matches. Another example is a study on anaerobic performance, which was investigated by using the 30 s Wingate test. The researchers stated that an acrophase was seen at 17:00–18:00 hours for Pmax and Ppeak [11]. These findings were similar to those of other researchers who used the 15s or 30 s Wingate test to study short-time anaerobic performance [9].

Limited studies have investigated the effect of CR on vertical jump performances [12, 13, 14]. One such study was performed by Lopez-Samanes et al. [15], who investigated the effect of CR on tennis performance. In that study, significant increases were obtained in countermovement jumps (CMJs) in the afternoon compared to morning. Studies showed that the peak power of CMJs is significantly affected by CR when compared with squat jumps [7]. In the study of Heischmann et al. [16], it was recommended to avoid morning training sessions for collegiate basketball players. That study supported the other studies above, investigating CMJs and power output during the cycle of a day whereby jump height (JH) and power outputs were low in the morning.

To our knowledge, studies to date have only investigated the effect of CR on the CMJ, which is an important test using the SSC, while the DJ and related parameters such as ODH, RSI [2], and GCT are becoming more important indicators of the SSC [17, 18, 19]. The RSI [2] is especially useful to determine the ODH [17, 20]. It has been stated that training using the ODH increases the efficiency of SSC, which affects athletic performance in various sports [17, 20]. However, no study has investigated the effects of CR on DJ parameters yet. Therefore, the purpose of this study was to investigate the effect of CR, in terms of morning vs. evening training sessions on various DJ-associated parameters.

2. Methods

2.1 Subjects

A total of 33 healthy university students (men, $n=$ 16; women, $n=$ 17) aged between 19 and 28 years were included in this study as subjects (Table 1). Subjects were recruited from Hacettepe University’s Beytepe campus; they were students in the Faculty of Sport Sciences and participated in this study voluntarily. Each subject was informed about the procedure before the study. They agreed to refrain from any other physical activity until the end of the testing procedure, as fatigue could affect the performance during the test sessions. Subjects were invited for two test sessions with at least one day between the sessions. Subjects were assigned randomly to morning and evening sessions. All necessary permissions were obtained from the Non-interventional Clinical Research Ethics Board of Hacettepe University (GO 17/902).

Table 1
Description of participants

Parameters	Male ( $n=$ 17)				Female ( $n=$ 16)
	Min	Max	Mean	Std. Dev.	Min	Max	Mean	Std. Dev.
Age (year)	19	28	23.47	2.9	19	28	22.25	2.27
Height (cm)	170	188	178.84	5.5	152	186	166.83	9.53
Training age (Year)	3	18	8.94	3.92	4	21	10.13	3.93

Table 2

Physiological parameters of participants

Gender	Parameters	Mean	Std. Dev.	Sig.
Female ( $n=$ 16)	HRe (beats/min)	76.75	10.68	0.343
	HRm (beats/min)	80.06	12.90
	BTe ( ${}^{\circ}$ C)	36.41	0.45	0.04 ${}^{\ast}$
	BTm ( ${}^{\circ}$ C)	36.09	0.41
Male ( $n=$ 17)	HRe (beats/min)	79.94	10.03	0.0001 ${}^{\ast\ast}$
	HRm (beats/min)	73.88	8.97
	BTe ( ${}^{\circ}$ C)	36.36	0.36	0.002 ${}^{\ast\ast}$
	BTm ( ${}^{\circ}$ C)	35.94	0.54

BTe $=$ Body temperature evening, BTm $=$ Body temperature morning, HRe $=$ Heart rate evening, HRm $=$ Heart rate morning.

2.2 Experimental design

To determine the effect of CR on the DJ and its parameters, we used a cross-over design with two test sessions: before 10:00 as the morning session and after 15:00 as the evening session. Subjects were randomly assigned to either morning or evening sessions. Subjects performed DJs from drop heights between 20 cm and the height where RSI scores began to decrease, which is called the ODH. The DJ parameters of GCT, JH, and RSI were recorded for DJs at ODH. Resting heart rates and oral body temperatures were measured before each testing session.

2.3 Procedure

Subjects were randomly invited for two testing sessions during different time periods of the day. The morning session ended at 10:00 at the latest and the evening session did not start until 15:00. The resting period between sessions was at least one day. The procedure was explained and subjects were familiarized with the DJ protocol before the study.

2.4 Anthropometric measurements

Heights were measured by using a standard stadiometer (Holtain, UK). Measurements were taken from the floor to the top of the head while the subject was in the Frankfort plane. The participant’s head, shoulders, back, and buttocks were in contact with the stadiometer. Subjects stood shod during the measurements. Body mass was measured using an integrated digital platform scale with body composition analyzer (Tanita TBF-401A, USA). Body mass measurements were performed in both sessions.

2.5 Heart rate and temperature

Subjects were expected to be rested before each session. Therefore, they rested for 20 minutes in a sitting position. Resting heart rates were recorded at the end of the resting period. Heart rates were recorded using a heart rate monitor (POLAR S810, USA), while body temperatures were recorded orally using an OMRON MC-246 digital thermometer in the last five minutes of the resting period.

2.6 Drop jump test

The DJs were performed from jump boxes with heights between 20 and 60 cm. During these tests, subjects began by dropping from a box 20 cm in height. Heights were increased by 10 cm to 30 cm, and then each following jump height was increased by 5 cm. During DJs, subjects were instructed to step off the box, not jump off, and land with both legs on the jump platform without using their arms. They were also instructed to jump powerfully with the shortest contact time on the mat, without raising their legs, knees, or buttocks. Subjects jumped with a one-minute rest between each jump until the decrease of the RSI score. The JHs (cm), RSI scores (mm/ms), and GCTs (ms) scores were recorded using Smart Jump (Fusion, Australia).

2.7 Statistical analyses

The descriptive statistics of variations are shown in Table 1, including the means, standard deviations, minimums, and maximums of participants’ ages, weights, and heights and the heart rates and body temperatures for both testing sessions. The normal distribution was tested for all parameters using the Kolmogorov-Smirnov test ( $p>$ 0.05). The differences between testing sessions for all parametric parameters were tested using the paired samples t-test in both genders. ODH was the only parameter without normal distribution and comparison of ODH between the two testing sessions was done using the non-parametric paired Wilcoxon test. All statistical analysis was conducted using SPSS 23 software (IBM Corp., USA).

3. Results

Only 31.3% of the participants (men: 23.5%; women: 37.5%) were training regularly (at least four days a week) in various sport disciplines (60% volleyball, 20% football, 10% general fitness, 10% Taekwondo). The other participants were not actively participating in any sports, although they had long histories of involvement. Training ages are shown in Table 1 with other descriptive variables including age and height for both genders. The comparison of physiological parameters in both testing sessions for both genders is shown in Table 2. For women, the resting body temperature in the evening session was significantly higher than in the morning session ( $p<$ 0.05). For men, both heart rate and resting body temperature were significantly higher in the evening session than in the morning session ( $p=$ 0.0001 and $p=$ 0.002, respectively).

Figure 1.

The differences of optimal drop height (ODH) between morning and evening sessions in both genders.

Figure 2.

The differences of Jump heights (cm) between morning and evening sessions in both genders. ${}^{*}p<$ 0.01.

The changes of DJ parameters between the two sessions are shown in Figs 1–4. In Fig. 1, ODH differences are shown for both genders. According to our findings, ODH values increased in men; however, a decrease was seen women in the evening session (women: T $=$ 53.00, $p=$ 0.71, $z=$ $-$ 1.805, $\eta^{2}=$ $-$ 0.45; men: T $=$ 29.50, $p=$ 0.26, $z=$ $-$ 1.127, $\eta^{2}=$ $-$ 0.27). The ODH where the breaking point of the RSI occurred did not differ significantly between testing sessions in both genders. Differences in JH are shown in Fig. 2. While JHs were similar in both sessions for women ( $p=$ 0.70), a significant increase was found in men between the two testing sessions ( $p=$ 0.005, $d=$ 0.80). The findings for RSI were similar to those for JHs. Although RSI scores increased significantly in men ( $p=$ 0.006, $\eta^{2}=$ 0.77), RSI scores of women were similar between the two sessions. Clearly while JH and GCT increased, RSI decreased in women in the evening session. RSI also decreased in women in the evening session but these differences were not statistically significant ( $p>$ 0.05). An increase was seen in ODH in men while it decreased in women in the evening session.

Figure 3.

The differences of RSI between morning and evening sessions in both genders. ${}^{*}p<$ 0.01.

Figure 4.

The differences of ground contact time (GCT) between morning and evening sessions in both genders.

4. Discussion

The primary question of this study related to possible diurnal differences in the DJ and its parameters between morning and evening sessions and between genders. The main finding of this study was the significant differences in DJ parameters in men between the testing sessions, which was not seen in women. This finding confirms our hypothesis, but only in men. Despite the significance, all parameters in this study were affected by CR. In particular, JHs increased in the evening session for both genders. This increase might be related to the increase in body temperature, which was significantly higher in the evening session in both genders (women: $p=$ 0.04; men: $p=$ 0.002). It is also well known that warming up increases the temperature of muscles, which is also particularly effective in short-duration performances including power productions [21]. However, no warm-up protocol was used before any test sessions in this study. This finding in our study supports a previous study [21], which reported the effect of high body temperature on muscle strength and power output. In that study, the increase in body temperature increased muscle strength and power output, as well. Similar findings were reported in the study of Davies and Young [22]. They observed that higher body temperatures increased the contraction speed of muscles by 20 ms. According to that study, the rise of body temperatures increased the jumping and cycling power output. In a study by Taylor et al. [23], the increase of body temperature in the evening also affected the peak power, peak velocity, and peak force with JHs of CMJs. Increased body temperature may lead to an increase in carbohydrate utilization over fat as a fuel source and may also facilitate actin-myosin cross-bridge mechanics within the musculoskeletal unit [24].

It is well known that environmental and seasonal temperatures affect the body temperature [25]. However, the effect of environmental temperature on neuromuscular indicators like vertical jumps or sprinting is related to the duration of exercise. In the study of Dotan and Bar-Or [26], no effects of climate were seen on rectal temperature or Wingate anaerobic test performance. In the study of Racinais et al. [27], it was observed that skeletal muscle contractility was enhanced with time of day in a neutral climate (20.5 $\pm$ 1 ${}^{\circ}$ C $+$ 67% humidity), but it was not affected in a moderately warm and humid climate (29.5 $\pm$ 0.8 ${}^{\circ}$ C $+$ 74 $\pm$ 10% humidity). Our study was conducted at the beginning of summer in Turkey. The mean environmental temperature was over 25 ${}^{\circ}$ C and the laboratory temperature and humidity where the testing procedure was conducted were 21.5 ${}^{\circ}$ C and 55%, respectively. The testing environment was kept moderately warm and humid so that muscle contractility would not be affected by the conditions of the environment.

The other main finding of our study was the significant difference of JH and RSI in men in the evening session compared to the morning session ( $p=$ 0.005 and $p=$ 0.006, respectively). Both of them were significantly higher in the evening session. According to our findings, GCTs were similar in both testing sessions. Therefore, the significant difference of the RSI could be explained by the significance of JH. This finding for JH supports the studies of Castaingts et al. [12] and Taylor et al. [13], who also found higher JH values in evening sessions. Castaingts et al. [12] found 10.9 $\pm$ 4.5% higher JHs in DJ tests in the evening session. This difference was attributed to the affected triceps surae (TS) muscle from the daytime; TS muscles exhibited higher neuromuscular efficiency when DJs were performed in the evening. This supports the improvements of contractile and elastic properties in the evening, a claim that has been made in several other studies providing support that skeletal muscle strength, and power are higher in the afternoon and evening compared to morning. The TS muscle group and knee extensors, which are effective in vertical jump performance, are also among the muscle groups investigated in human subjects [28]. The ability to generate force depends on both peripheral and central mechanisms. It is stated that a central mechanism or a combination of both types of mechanisms is responsible during the CR in force production [29].

Similar results for the CMJ were found by Taylor et al. [13]. In that study, it was suggested that monitoring CMJ performance would be more useful in the evening. Despite those results, Bernard et al. [14] found higher JHs from a multi-jump test in the afternoon than in the evening. The evening JHs were also higher than those in the morning, similar to other studies, some of which have been explained above. Di Cagno et al. [30] used a hopping test (flight time and GCT) and DJ (flight time) to interpret reactive strength. In only the hopping tests, flight times were significantly higher in the afternoon in both female gymnasts (ages between 12 and 13 years) and the control group.

To our knowledge, our study is the first to investigate the effect of CR on RSI and ODH in DJs. One of the interesting findings of our study was the non-significant differences of DJ parameters between testing sessions in women. In a study by Melhim [31], a significant effect of CR was found for peak power and mean power of the Wingate anaerobic test in female students ( $p=$ 0.03 and $p=$ 0.01, respectively). These parameters were significantly higher (16% and 15%, respectively) at 15:00 and 21:00 hours than at 03:00 [31]. In another study conducted by Mhenni et al. [32], the participants were women handball players. The authors found significant differences between morning and evening sessions for handgrip test ( $p=$ 0.0013), ball-throwing velocity test ( $p=$ 0.0027), modified agility T-test ( $p<$ 0.001), and repeated shuttle-sprint and jump ability test (sprint: $p=$ 0.001; jump: $p=$ 0.026). However, no significant differences between sessions were seen for the best JHs. It was stated that the best JHs were not affected by time-of-day testing in women, which supports our findings. One of the reasons for these findings could be the effect of testosterone, which maintains anabolism by promoting protein synthesis within the muscular system [24]. Evidence in the literature demonstrates the differences of jump performances according to testosterone levels between men and women. For example, a significant positive relationship was found between testosterone level and vertical jump performance in the study of Cardinale and Stone [33].

Testosterone and cortisol concentrations have similar patterns during the daytime. Both hormones are at their highest levels in the morning. Despite the decrease of testosterone and cortisol throughout the day, it is stated that the ratio of testosterone and cortisol is important in evening resistance training. Evening time could be the best for protein accretion due to an increased testosterone and cortisol ratio and that increase in the testosterone/cortisol ratio is due to the constraining effect of cortisol on testosterone [34], which seems to be less in the evening [7].

5. Conclusion

Temperature monitoring of RSI in the DJ test is becoming more common to determine the optimal workload in plyometrics. The findings of our study show that there is no optimal monitoring time of day for women athletes. According to these findings, fewomen may train explosive power efficiently by using DJs in both the morning and evening, while evening is the optimal time of day for this objective in men. These findings may be useful for practitioners who are planning to develop and monitor JH, GCT, or RSI by using DJs in their training programs.

Footnotes

Conflict of interest

None to declare.

References

Komi

. Stretch-shortening cycle: a powerful model to study normal and fatigued muscle. J Biomech. 2000; 33(10): 1197-206.

Vaczi

Nagy

Koszegi

Ambrus

Bogner

Perlaki

, et al. Mechanical, hormonal, and hypertrophic adaptations to 10 weeks of eccentric and stretch-shortening cycle exercise training in old males. Exp Gerontol. 2014; 58: 69-77.

Byrne

Browne

Byrne

Richardson

. Interday Reliability of the Reactive Strength Index and Optimal Drop Height. J Strength Cond Res. 2017; 31(3): 721-6.

Gabbett

. The training-injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016: bjsports-2015-095788.

Soligard

Schwellnus

Alonso

J-M

Bahr

Clarsen

Dijkstra

, et al. How much is too much? (Part 1); International Olympic Committee consensus statement on load in sport and risk of injury. Br J Sports Med. 2016; 50(17): 1030-41.

Bourdon

Cardinale

Murray

Gastin

Kellmann

Varley

, et al. Monitoring athlete training loads: consensus statement. Int J Sport Physiol. 2017; 12(Suppl 2): S2-161-S2-70.

Hatfield

Nicoll

Kraemer

. Effects of Circadian Rhythm on Power, Force, and Hormonal Response in Young Men. J Strength Cond Res. 2016; 30(3): 725-32.

Vitale

Weydahl

. Chronotype, Physical Activity, and Sport Performance: A Systematic Review. Sports Med. 2017; 47(9): 1859-68.

Thun

Bjorvatn

Flo

Harris

Pallesen

. Sleep, circadian rhythms, and athletic performance. Sleep Med Rev. 2015; 23: 1-9.

10.

Ryan

Bahnert

McBrien

Siegler

Lovell

. The effect of chronotype upon physical performance during Australian rules football matches scheduled in the morning, afternoon and evening. Journal of Australian Strength and Conditioning. 2015; 23(6): 101-4.

11.

Souissi

Gauthier

Sesboüé

Larue

Davenne

. Circadian rhythms in two types of anaerobic cycle leg exercise: force-velocity and 30-s Wingate tests. Int J Sports Med. 2004; 25(1): 14-9.

12.

Castaingts

Martin

, Hoecke

Perot

. Neuromuscular efficiency of the triceps surae in induced and voluntary contractions: morning and evening evaluations. Chronobiology International. 2004; 21(4-5): 631-43.

13.

Taylor

K-L

Cronin

Gill

Chapman

Sheppard

. Sources of variability in iso-inertial jump assessments. Int J Sport Physiol. 2010; 5(4): 546-58.

14.

Bernard

Giacomoni

Gavarry

Seymat

Falgairette

. Time-of-day effects in maximal anaerobic leg exercise. Eur J Appl Physiol O. 1997; 77(1-2): 133-8.

15.

Lopez-Samanes

Moreno-Perez

Mate-Munoz

Dominguez

Pallares

Mora-Rodriguez

, et al. Circadian rhythm effect on physical tennis performance in trained male players. J Sport Sci. 2017; 35(21): 2121-8.

16.

Heishman

Curtis

Saliba

Hornett

Malin

Weltman

. Comparing Performance During Morning vs. Afternoon Training Sessions in Intercollegiate Basketball Players. J Strength Cond Res. 2017; 31(6): 1557.

17.

Byrne

Moran

Rankin

Kinsella

. A Comparison of Methods Used to Identify ‘Optimal’ Drop Height for Early Phase Adaptations in Depth Jump Training. J Strength Cond Res. 2010; 24(8): 2050-5.

18.

Flanagan

Comyns

. The use of contact time and the reactive strength index to optimize fast stretch-shortening cycle training. Strength & Conditioning Journal. 2008; 30(5): 32-8.

19.

Markwick

Bird

Tufano

Seitz

Haff

. The Intraday Reliability of the Reactive Strength Index Calculated From a Drop Jump in Professional Men’s Basketball. Int J Sport Physiol. 2015; 10(4): 482-8.

20.

McClymont

, editor Use of the reactive strength index (RSI) as an indicator of plyometric training conditions. Science in Football V: The Proceedings of the Fifth World Congress on Science and Football London, Routledge, 2005.

21.

Bergh

Ekblom

. Influence of muscle temperature on maximal muscle strength and power output in human skeletal muscles. Acta Physiologica Scandinavica. 1979; 107(1): 33-7.

22.

Davies

Young

. Effect of temperature on the contractile properties and muscle power of triceps surae in humans. J Appl Physiol. 1983; 55(1): 191-5.

23.

Taylor

Cronin

Gill

Chapman

Sheppard

. Warm-up affects diurnal variation in power output. Int J Sports Med. 2011; 32(3): 185-9.

24.

Teo

Newton

McGuigan

. Circadian rhythms in exercise performance: implications for hormonal and muscular adaptation. Journal of Sports Science & Medicine. 2011; 10(4): 600.

25.

Racinais

Oksa

. Temperature and neuromuscular function. Scand J Med Sci Spor. 2010; 20: 1-18.

26.

Dotan

Bar-Or

. Climatic heat stress and performance in the Wingate Anaerobic Test. Eur J Appl Physiol O. 1980; 44(3): 237-43.

27.

Racinais

Blonc

Jonville

Hue

. Time of day influences the environmental effects on muscle force and contractility. Medicine & Science in Sports & Exercise. 2005; 37(2): 256-61.

28.

Zhang

Dube

Esser

. Working around the clock: circadian rhythms and skeletal muscle. J Appl Physiol. 2009; 107(5): 1647-54.

29.

Küüsmaa

Sedliak

Häkinen

. Effects of time-of-day on neuromuscular function in untrained men: Specific responses of high morning performers and high evening performers. Chronobiology International. 2015; 32(8): 1115-24.

30.

di Cagno

Battaglia

Giombini

Piazza

Fiorilli

Calcagno

, et al. Time of day – effects on motor coordination and reactive strength in elite athletes and untrained adolescents. Journal of Sports Science & Medicine. 2013; 12(1): 182.

31.

Melhim

. Investigation of circadian rhythms in peak power and mean power of female physical education students. Int J Sports Med. 1993; 14(6): 303-6.

32.

Mhenni

Michalsik

Mejri

Yousfi

Chaouachi

Souissi

, et al. Morning – evening difference of team-handball-related short-term maximal physical performances in female team handball players. J Sport Sci. 2017; 35(9): 912-20.

33.

Cardinale

Stone

. Is testosterone influencing explosive performance? J Strength Cond Res. 2006; 20(1): 103.

34.

Sherman

Lerner

Josephs

Renshon

Gross

. The interaction of testosterone and cortisol is associated with attained status in male executives. Journal of Personality and Social Psychology. 2016; 110(6): 921.

The effect of circadian rhythm on drop jump performance

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

2.1 Subjects

Table 1 Description of participants

2.3 Procedure

2.4 Anthropometric measurements

2.5 Heart rate and temperature

2.6 Drop jump test

2.7 Statistical analyses

3. Results

5. Conclusion

Footnotes

Conflict of interest

References

Table 1
Description of participants