Summary:
Τraining load (TL) is defined as any kind of training stimulus received by the athlete. Training load can be described as being either external or internal, depending if we are referring to measurable aspects occurring externally or internally to the athlete. Quality and quantity of exercise determine the external load, which is defined as the physical work prescribed in the training program. Internal load refers to all the psychophysiological responses that external load causes to the athlete. Rate of perceived exertion (RPE) is a scale that measures internal load in atletes. Rate of perceived recovery (RPR) is, also, a scale that assesses the athlete's ability to exercise the following day, and in that way, it can be an additional tool for studying their adaptability to training stress in the short period of the night between two training sessions.
In team sports, such as volleyball, the application of appropriate training loads (TL) has been a main subject of research in recent years, in order to maximize athletes' performance and to avoid overtraining and injuries. Therefore, monitoring TL in combination with examining other parameters, such as, fatigue and well-being parameters, autonomous nervous system (ANS) function, neuromuscular adaptations and sleep quality, can give useful information that help coaches achieve that goal.
Vertical jump is a key skill in volleyball, as it is used in attacking, blocking and serving. As a result, countermovement jump (CMJ) is important to be included in the training plan, and to be quantified in each microcycle, as competitions usually take place at the end of the week. CMJ is, however, considered as an index to evaluate neuromuscular adaptations in volleyball, as it can be used to assess the power of the lower limbs. Several studies have examined the relationship between CMJ and TL, finding, however, conflicting results.
The Autonomic Nervous System (ANS) consists of Sympathetic and Parasympathetic Nervous System. Sympathetic Nervous System is related to situations of tension (“fight or flight”). On the contrary, Parasympathetic Nervous System is related to states of calmness ("resting or digesting"). Heart does not beat like a metronome, but it adapts based on the stimuli it receives from the environment. Heart Rate Variability (HRV) refers to the variation in the time interval between successive heartbeats. It is considered as an important indicator for evaluating the ability of the ANS to regulate cardiac function, when it receives physical and psychological stimuli. High HRV measures have been related to a generally better state of health, as it shows that heart has the ability to better adapt to these stimuli. HRV is calculated by measuring certain parameters, which are studied either through time analysis or through spectral (frequency) analysis. As far as time analysis is concerned, the main parameteres are: a) RMSSD (square root of the mean value of the sum of the squares of the differences between consecutive heartbeats), b) NN50 (the number of consecutive N-N intervals with a difference of more than 50ms), as well as its percentage expression (%) (pNN50), and c) NN100 (the number of consecutive N-N intervals with a difference of more than 100ms), as well as its percentage expression (%) (pNN100). The above parameters are related to parasympathetic function. Several studies have also used R-R intervals (the mean value of the R-R intervals), as well as SDNN (the standard deviation of the N-N intervals). Frequency domain analysis (spectral analysis) estimates the distribution of the absolute or relative power of the signal in 4 frequency bands (Ultra Low Frequencies – ULF, Very Low Frequencies – VLF, Low Frequencies – LF, High Frequencies – HF). Finally, the Poincaré graph (SD1, SD2), which is a method based on non-linear dynamics, is also, commonly used. In sports, HRV is considered an indicator of the athlete's adaptability to training stimuli. A significant number of studies involving swimming, rugby, american football, and soccer has shown that when high training loads were applied to athletes, HRV was negatively affected. In volleyball, HRV can be a useful tool for the coaches to properly organize training loads during the season, in order to avoid overtraining and injury of their athletes.
Sleep is a necessary element, both for recovery and performance in sports. Sleep quality can be affected by various factors, which are connected with athletes' psychology or their daily habits. More specifically, high competition, demanding training programs, or anxiety about upcoming matches, are quite stressful factors, which in turn affect athletes' sleep quality. In addition, difficult training hours, late-night games, and also continuous trips, can have a negative impact in athletes' sleep. Finally, daily habits before sleep, such as exposure to artificial light, as well as dietary habits, can affect athletes' sleep quality. Sleep disorders can be expressed through insomnia, interrupted sleep, or through the difficulty in waking up in the morning, while in more serious cases, they can be expressed through obstructive sleep apnea, circadian rhythm disorders, or restless legs symptoms. As a consequence, athletes' sleep has shorter duration, that makes it insufficient and leads them to increased and prolonged fatigue during the day. The measurement of sleep quality often includes self-rated questionnaires, in which athletes present their subjective feeling in the evaluation part. Pittsburgh Sleep Quality Index (PSQI) is one of the most widely used questionnaires, which assesses sleep quality and disturbances. It gives us information on 7 categories of sleep disorders, from which derive 7 separate scores. Their sum gives us the final score of the questionnaire.
Lack of research concerning correlations between all these parameters above, was the main reason why the present research was conducted. The objective of this study was to examine the correlation between: TL and RPE , TL and RPR , TL and CMJ , TL and HRV , TL and Sleep , RPE and RPR , RPE and CMJ , RPE and HRV , RPE and Sleep , CMJ and RPR , CMJ and HRV , CMJ and Sleep , HRV and RPR , HRV and Sleep , Sleep and RPR.
Method: 27 elite14-15 aged female volleyball players participated in this study. During their stay in a 20-day training camp for the final selection of the National team of Greece, TL, RPE and RPR were monitored on a daily basis, while CMJ, HRV and Sleep Quality were recorded at the end of the camp. Sleep quality evaluation was done by the athletes themselves, using Pittsburgh Sleep Quality Index (PSQI) and Sleep and Memory (Clinic Version) Questionnaire. Mean TL (mTL), mean RPE (mRPE) and mean RPR (mRPR) were calculated. The Pearson's correlation test was used to verify the relationship between the parameters. Data were analyzed using SPSS software. The level of significance was less than 5% (p<=0.05). Results: A positive correlation was observed between mTL and mRPE (r=0.665, p=0.005). No correlation was observed between mTL and mRPR, nor between mRPE and mRPR. CMJ was positively correlated with PSQI general score (r=0.576, p=0.031). No correlation of HRV variables with mTL, nor with mRPE was observed. The LF/HF ratio was negatively correlated with mRPR (r=-0.588, p=0.027) and positively correlated with the difficulty of athletes to stay awake in-next day-social activities (r=0.563, p=0.023). SDNN, pNN50, RMSSD, SD1 and SD2 were negatively correlated with athletes' self-reported score in the the question of PSQI that concerned sleep quality (r=-0.568, p=0.022, r=-0.642, p=0.007, r=-0.556, p=0.025, r= -0.559, p=0.25, r=-0.572, p=0.20 respectively). Resting HR was positively correlated with the frequency of taking sleeping medication (r=0.806, p=0.000). The athletes' Fitness Level in CardioScan was positively correlated with the time they woke up in the morning (r=0.518, p=0.028) and negatively with the frequency of taking sleeping medication (r=-0.488, p=0.040). Conclusions: The mTL applied was found to be of submaximal intensity, and was not able to affect HRV parameters. The athletes' recovery status was good, based on the mRPR values. In addition, CMJ appeared to be a less sensitive index to changes in TL than RPE. Finally, good sleep quality, as stated by the athletes, was also reflected in the ANS function. However, further research is needed in order to make safer and more specific conclusions, given the number and nature of the parameters analyzed.
