Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players

Twenty female athletes of the Chinese People's Liberation Army team (age = 18.60 ± 3.60 years) participated in the study. Participant characteristics are described in Table 1. All participants were healthy and were not using medications regularly or temporarily during the measurements. Athletes were excluded if they had participated in less than 80% of the scheduled team physical training and basketball sessions for the last 3 months or used any kind of nutritional supplements or pharmacologic agents. All participants provided written informed consent, and the study was approved by the Ethical Committee of the China Institute of Sport Science.

We used a randomized parallel pretest-posttest design. Participants were assigned randomly to either a red-light therapy intervention group (n = 10) or non–red-light therapy intervention group (placebo group, n = 10). Measurements were collected at preintervention (baseline) and postintervention (14 days). The exercise training schedule of the 2 groups was unchanged during the 14 days; the red-light treatment group used a red-light therapy instrument every night for total body irradiation for 30 minutes. The training routine of the athletes during the 14 intervention days included 12 exercise sessions with the following specifications: 2 hours of morning training, 2 hours of afternoon training, and no training on Sunday.

The red-light treatment participants lay in the supine position, and continuous illumination was performed using noncoherent red light from a whole-body red-light treatment machine (Shanghai Dayou PDT Technology Co, Ltd, Shanghai, China) with an average wavelength of 658 nm and light dose of 30 J/cm². The whole body received the phototherapy treatment (Figure 1). In general studies, investigators have used 14 days^20,21  or 7 days²²  as 1 session period, so we chose 14 days as a trial time. The placebo participants also lay in the supine position under the red-light device but did not receive any light illumination. All participants wore swimsuits to enhance irradiation from the device and were blind to the treatment.

Sleep quality was measured by the Chinese version of the PSQI.¹⁷  The 19-item measure assesses sleep quality and disturbances over a half-month time interval. The total PSQI score ranges from 0 to 21, and higher scores reflect poorer-quality sleep.¹⁷  The 7 items of this instrument measure several aspects of insomnia: difficulties with onset and maintenance of sleep, satisfaction with the current sleep pattern, interference with daily functioning, noticeable impairment attributed to sleep problems, degree of distress, and concern caused by any sleeping problems.

Participants were instructed to complete as many laps as possible on a 400-m outdoor track during the 12-minute test period. Emphasis was placed on pacing oneself throughout the test. The test administrators (J.Z., D.L., and J.X.) counted the laps completed during the 12-minute test period while calling out the time elapsed at 3, 6, and 9 minutes and orally encouraging the participants. At the end of the 12-minute period, the test administrator instructed the participants to stop and used a measuring wheel to determine the fraction of the last lap completed by each participant. This distance was added to the distance determined by the number of laps completed to give the total distance covered during the test.

In humans, the serum level of melatonin, which is derived mainly from the pineal gland, demonstrates a clear increase at night and a decrease during the day.^23,24  Given that the masking effects of activities (eg, exercise, sleep, and food intake^25,26) have little effect on the daily pattern of the circulating melatonin level, melatonin secretion appears to directly reflect the function of the biological clock as a specific marker of circadian rhythm.²⁷  We drew blood samples in the morning (8:00 am) of preintervention and postintervention. Melatonin in the serum was measured in pictograms per milliliter using an enzyme-linked immunosorbent assay kit (Melatonin ELISA; IBL, Hamburg, Germany).

Data were analyzed using descriptive statistics, 2-way analyses of variance (ANOVAs), and t tests for independent means. Isolated comparisons between groups (experimental, control) and times (preintervention, postintervention) were performed only in cases where time × group interactions were found. We used Pearson product moment correlation coefficients to determine the relationships among sleep quality, serum melatonin, and endurance performance. The α level was set at .05. We used SPSS (version 16.0; IBM Corporation, Armonk, NY) for data analysis.

We found no differences in any of the baseline characteristics between the groups.

We found an effect for group (F_1,18 = 5.62, P = .03) and a time × group interaction for global PSQI scores (F_1,18 = 5.66, P = .03; Figure 2). At preintervention, we found no difference between the groups (t₁₈ = −0.53, P = .60). At postintervention, participants in the red-light treatment group demonstrated greater improvement in global PSQI scores than the placebo group (t₁₈ = −4.55, P < .001). Descriptive statistics and statistical values for the PSQI subscores are listed in Table 2. Among the subscores, we found a time × group interaction for subjective sleep quality (F_1,18 = 6.70, P = .02) and effects of group for sleep duration (F_1,18 = 5.36, P = .03) and sleep latency (F_1,18 = 5.65, P = .03). We noted an effect of time for daytime dysfunction (F_1,18 = 6.40, P = .02). We did not observe an effect of group or a time × group interaction for habitual sleep efficiency (F_1,18 = 2.49, P = .13 and F_1,18 = 2.84, P = .11, respectively) or sleep disturbance (F_1,18 = 0.21, P = .65 and F_1,18 = 3.32, P = .09, respectively) variables.

We found an effect for group (F_1,18 = 18.84, P < .001) and a time × group interaction for serum melatonin level (F_1,18 = 14.08, P = .001). At preintervention, we demonstrated no difference between the red-light treatment (22.2 ± 7.2 pg/mL) and placebo (21.7 ± 6.8 pg/mL) groups (t₁₈ = 0.17, P = .87). At postintervention, participants in the red-light treatment group (38.8 ± 6.7 pg/mL) demonstrated greater improvement in serum melatonin level than the placebo group (23.8 ± 7.3 pg/mL; t₁₈ = 4.96, P < .001; Figure 3).

We noted an effect of time for distance (F_1,18 = 12.76, P = .004). We observed a trend toward improvement but no time × group interaction (F_1,18 = 1.72, P = .22). A difference was found between preintervention and postintervention of the red-light treatment group (t₁₈ = 3.54, P = .005; Figure 4).

We demonstrated a correlation between changes in global PSQI and serum melatonin levels (r = −0.695, P = .006; Table 3). We also saw a trend toward a negative relationship between change in global PSQI and distance of the 12-minute run test at preintervention and postintervention for all participants (r = −0.353, P = .07; Table 3). In addition, when the results of the postintervention were analyzed alone, we found a negative correlation between change in the distance of the 12-minute run test and global PSQI (r = −0.579, P = .02).

Our results indicated that a 14-day program of red-light treatment improved sleep and serum melatonin levels. Although the statistical analysis did not reveal differences between groups for running distance in the aerobic exercise test, the percentage increase in the red-light treatment group (12.8%) was higher than the percentage increase in the control group (5.5%; P < .05).

The PSQI revealed that the improvements in global PSQI scores and sleep quality were greater at postintervention in the red-light treatment group than in the placebo group. In addition, we found an effect of time for daytime dysfunction (F_1,8 = 6.40, P = .02). Sack et al²⁸  suggested a role of melatonin in facilitating sleepiness during the night by inhibiting a central nervous system wakefulness-generating system. The positive effect seen in our study may be due to relatively higher melatonin levels after the red-light illumination. Our results are in accordance with those reported in previous studies, showing that melatonin might be a principal component of red-light therapy.¹²  In their analysis of the effects of light on melatonin levels and rhythms in humans, Wright and Lack²⁹  showed that, whereas shorter wavelengths of blue (430 nm) and green (540 nm) light suppress salivary melatonin and shift the melatonin rhythm, red light (610 nm and 660 nm) has no effect on melatonin suppression and slightly shortens the time before dim-light onset of melatonin secretion. Recently, Figueiro and Rea²²  demonstrated that blue light reduced nocturnal levels of melatonin, whereas red light increased them. However, our observations contradicted those reported in studies of adults with insomnia in which researchers³⁰  reported negative relationships between the red-light condition and improved sleep variables and daytime symptoms. Conflicting results in the literature may stem from studying different participants. In our study, the participants were female basketball players who did not have severe insomnia.

We observed an effect of time on distance (F_1,8 = 12.76, P = .004), such that 12-minute run distance was longer after 14 days of red-light illumination in basketball players. For the 12-minute run distance, an effect was noted for time but not for group; no time × group interaction was seen. Therefore, we could not draw a clear conclusion that red-light illumination induced positive changes in endurance performance among basketball players. With regard to the association of red light and exercise, the data are quite scarce. As far as we know, only 1 study³¹  of red light and exercise in human participants has been published. The study was carried out in healthy, physically active male volunteers, and treatment with light-emitting diodes produced a smaller decrease in maximal isometric torque after high-intensity concentric isokinetic exercise. Ihsan³²  demonstrated that laser promoted arteriolar vasodilation and improved the peripheral microcirculation. In addition, phototherapy could improve the muscle regeneration after exercise.³³  Therefore, observations by us and by Baroni et al³¹  may be mainly related to increased arteriolar vasodilation and peripheral microcirculation after red-light illumination.

We found a correlation between changes in global PSQI and serum melatonin levels (r = −0.695, P = .006). A negative relationship existed between decreases in sleep quality and improvements in endurance performance as determined by 12-minute run distance, but this was only a trend (r = −0.353, P = .07). We also demonstrated a correlation between sleep quality and distance of the 12-minute run test during the postintervention period. This in part may be due to sleep providing recovery from autonomic reactivity, psychoemotional tension, and hormonal responses.³⁴  These results suggest that endurance performance was mediated by mechanisms other than sleep quality alone.

We have demonstrated that red-light illumination positively affected sleep quality and endurance performance variables in Chinese female basketball players. Based on previous studies,^{6,12,14,15,33}  we can infer that red-light treatment contributes to increased melatonin secretion in the pineal gland and muscle regeneration. To our knowledge, we are the first to demonstrate the positive effects of red-light treatment on sleep and aerobic performance, which is an interesting link with practical application to sports training. Although more studies involving phototherapy, sleep, and exercise performance need to be performed, red-light treatment is a possible nonpharmacologic and noninvasive therapy to prevent sleep disorders after training.

This research project was supported by National Key Technologies R&D Program Fund of China (2006BAK37B06).

We thank Professor Craig G. Crandall for editing and Dr James Pearson for proofreading the manuscript. We also thank Bin Fan and Qingde Shi for analyzing and entering the data; Baoxin Feng, Peifang Zong, Wenyuan Shang, Weiying Zhang, and Pengfei Li for their technical assistance; and our volunteers for their willingness to participate in this project.