Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8986.1997.tb02140.x

Heart rate variability: Origins, methods, and interpretive caveats

Soccer is the most popular sport in the world and is performed by men and women, children and adults with different levels of expertise. Soccer performance depends upon a myriad of factors such as technical/biomechanical, tactical, mental and physiological areas. One of the reasons that soccer is so popular worldwide is that players may not need to have an extraordinary capacity within any of these performance areas, but possess a reasonable level within all areas. However, there are trends towards more systematic training and selection influencing the anthropometric profiles of players who compete at the highest level. As with other activities, soccer is not a science, but science may help improve performance. Efforts to improve soccer performance often focus on technique and tactics at the expense of physical fitness. During a 90-minute game, elite-level players run about 10 km at an average intensity close to the anaerobic threshold (80-90% of maximal heart rate). Within this endurance context, numerous explosive bursts of activity are required, including jumping, kicking, tackling, turning, sprinting, changing pace, and sustaining forceful contractions to maintain balance and control of the ball against defensive pressure. The best teams continue to increase their physical capacities, whilst the less well ranked have similar values as reported 30 years ago. Whether this is a result of fewer assessments and training resources, selling the best players, and/or knowledge of how to perform effective exercise training regimens in less well ranked teams, is not known. As there do exist teams from lower divisions with as high aerobic capacity as professional teams, the latter factor probably plays an important role. This article provides an update on the physiology of soccer players and referees, and relevant physiological tests. It also gives examples of effective strength- and endurance-training programmes to improve on-field performance. The cited literature has been accumulated by computer searching of relevant databases and a review of the authors' extensive files. From a total of 9893 papers covering topics discussed in this article, 843 were selected for closer scrutiny, excluding studies where information was redundant, insufficient or the experimental design was inadequate. In this article, 181 were selected and discussed. The information may have important implications for the safety and success of soccer players and hopefully it should be understood and acted upon by coaches and individual soccer players.

http://carlocapelli.it/ftp/didattica/master calcio/bibliografia_essenziale/stolen_et_al_2005.pdf

Physiology of Soccer: An Update

Fast Fourier Transform

Given the importance of the autonomic nervous system to cardiovascular health, it is not surprising that there is and has been great interest in measurements of human sympathetic and vagus nerve traffic as tools that might inform physiological and pathophysiological mechanisms. Pagani and coworkers1 advanced the provocative notion that the instantaneous balance between sympathetic and vagal nerve activities can be captured by a single number, obtained by dividing RR-interval spectral power centered at ≈0.1 Hz by spectral power centered at higher, primarily respiratory frequencies. This ratio, or sympathovagal balance, has been embraced with great enthusiasm2 because it offers new possibilities for understanding dynamic, critically important autonomic interrelations in humans by the use of totally noninvasive, unobtrusive means.3

The broad bases for this mathematical treatment are as follows: (1) 0.1-Hz RR intervals are importantly mediated by fluctuations of sympathetic nerve activity; (2) higher-frequency RR-interval rhythms are mediated almost exclusively by fluctuations of vagal-cardiac nerve activity; and (3) physiological interventions tend to provoke reciprocal changes of sympathetic and vagal neural outflows. Sympathovagal balance, the ratio of these periodicities, is taken to reflect the balance between the opposing neural mechanisms. This review examines the physiological foundations of sympathovagal balance.

The ECG is recorded with the subject in a steady state (when rhythms are stationary) for a period sufficiently long to define events occurring over frequencies of interest. RR-interval spectral power is calculated from this series of intervals with an autoregressive algorithm, which yields center frequencies and absolute power of component fluctuations, based on a model whose order (the number of parameters) is selected automatically to minimize Akaike’s information criterion statistic.4 (The statistical uncertainty and consequences of the automatic selection of the autoregressive model have not been defined fully; however, it is clear that the model order importantly determines both …

Sympathovagal Balance A Critical Appraisal

In soccer, the players perform intermittent work. Despite the players performing low-intensity activities for more than 70% of the game, heart rate and body temperature measurements suggest that the average oxygen uptake for elite soccer players is around 70% of maximum (VO(2max). This may be partly explained by the 150 - 250 brief intense actions a top-class player performs during a game, which also indicates that the rates of creatine phosphate (CP) utilization and glycolysis are frequently high during a game. Muscle glycogen is probably the most important substrate for energy production, and fatigue towards the end of a game may be related to depletion of glycogen in some muscle fibres. Blood free-fatty acids (FFAs) increase progressively during a game, partly compensating for the progressive lowering of muscle glycogen. Fatigue also occurs temporarily during matches, but it is still unclear what causes the reduced ability to perform maximally. There are major individual differences in the physical demands of players during a game related to physical capacity and tactical role in the team. These differences should be taken into account when planning the training and nutritional strategies of top-class players, who require a significant energy intake during a week.

https://www.olympiatoppen.no/fagomraader/idrettsernaering/Fagstoff/fotball/media3886.media

Physical and metabolic demands of training and match-play in the elite football player.

The rhythmic components of heart rate variability (HRV) can be separated and quantitatively assessed by means of power spectral analysis. The powers of high frequency (HF) and low frequency (LF) components of HRV have been shown to estimate cardiac vagal and sympathetic activities. The reliability of these spectral indices, as well as that of LF/HF ratio as a marker of autonomic interaction at rest and during exercise, is briefly reviewed. Modifications in autonomic activities induced by different physiological conditions, e.g. hypoxia exposure, training, and water immersion, have been found in HRV power spectra at rest. The changes in HF and LF powers and in LF/HF ratio observed during exercise have been shown not to reflect the decrease in vagal activity and the activation of sympathetic system occurring at increasing loads. HF peak was recognised in power spectra in the entire range of relative intensity, being responsible for the most part of HR variability at maximal load. LF power did not change during low intensity exercise and decreased to negligible values at medium-high intensity, where sympathetic activity was enhanced. There was no influence from factors such as fitness level, age, hypoxia, and blood distribution. In contrast, a dramatic effect of body position has been suggested by the observation that LF power increased at medium-high intensities when exercising in the supine position. The increased respiratory activity due to exercise would be responsible of HF modulation of HR via a direct mechanical effect. The changes in LF power observed at medium-high intensity might be the expression of the modifications in arterial pressure control mechanisms occurring with exercise. The finding of opposite trends for LF rhythm in supine and sitting exercises suggests that different readjustments might have occurred in relation to different muscular inputs in the two positions.

Heart rate variability and autonomic activity at rest and during exercise in various physiological conditions.

The time course of heart rate (HR) and venous blood norepinephrine concentration [NE], as an expression of the sympathetic nervous activity (SNA), was studied in six sedentary young men during recovery from three periods of cycle ergometer exercise at 21%±2.8%, 43%±2.1% and 65%±2.3% of\(\dot V_{o_{2max} } \) respectively (mean±SE). The HR decreased mono-exponentially withτ values of 13.6±1.6 s, 32.7±5.6 s and 55.8±8.1s respectively in the three periods of exercise. At the low exercise level no change in [NE] was found. At medium and high exercise intensity: (a) [NE] increased significantly at the 5th min of exercise (Δ[NE]=207.7±22.5 pg·ml−1 and 521.3±58.3 pg·ml−1 respectively); (b) after a time lag of 1 min [NE] decreased exponentially (τ=87 s and 101 s respectively); (c) in the 1st min HR decreased about 35 beats · min−1; (d) from the 2nd to 5th min of recovery HR and [NE] were linearly related (100 pg·ml−1Δ[NE]5 beats ·min−1). In the 1st min of recovery, independent of the exercise intensity, the adjustment of HR appears to have been due mainly to the prompt restoration of vagal tone. The further decrease in HR toward the resting value could then be attributed to the return of SNA to the pre-exercise level.

Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in man

The surface mechanomyogram (MMG) (detectable at the muscle surface as MMG by accelerometers, piezoelectric contact sensors or other transducers) is the summation of the activity of single motor units (MUs). Each MU contribution is related to the pressure waves generated by the active muscle fibres. The first part of this article will review briefly the results obtained by our group studying the possible role of motor unit recruitment and firing rate in determining the characteristics of the MMG during stimulated and voluntary contractions. The second part of this article will study the MMG and EMG during a short isometric force ramp from 0 to 90% of the maximal voluntary contraction (MVC) in fresh and fatigued biceps brachii. The aim is to verify whether changes in motor unit activation strategy in voluntarily fatigued muscle could be specifically reflected in the time and frequency domain parameters of the MMG. MMG-RMS vs. %MVC: at fatigue the MMG-RMS did not present the well known increment, when effort level increases, followed by a clear decrement at near-maximal contraction levels. MMG-MF vs. %MVC: compared to fresh muscle the fatigued biceps brachii showed an MF trend significantly shifted towards lower values and the steeper MF increment, from 65 to 85% MVC, was not present. The alteration in the MMG and EMG parameters vs. %MVC relationships at fatigue seems to be related to the impossibility of recruiting fast, but more fatigable MUs, and to the lowering of the global MUs firing during the short isometric force ramp investigated.

The surface mechanomyogram as a tool to describe the influence of fatigue on biceps brachii motor unit activation strategy. Historical basis and novel evidence.

The contracting muscle generates a low frequency sound detectable at the belly surface, ranging from 11 to 40 Hz. To study the relationship between the muscular sound and the intensity of the contraction a sound myogram (SMG) was recorded by a contact sensor from the biceps brachii of seven young healthy males performing 4-s isometric contractions from 10% to 100% of the maximal voluntary contraction (MVC), in 10% steps. Simultaneously, the electromyogram (EMG) was recorded as an index of muscle activity. SMG and EMG were integrated by conventional methods (iSMG and iEMG). The relationship between iSMG and iEMG vs MVC% is described by parabolic functions up to 80% and 100% MVC respectively. Beyond 80% MVC the iSMG decreases, being about half of its maximal value at 100% MVC. Our results indicate that the motor unit recruitment and firing rate affect the iSMG and iEMG in the same way up to 80% MVC. From 80% to 100% MVC the high motor units' discharge rate and the muscular stiffness together limit the pressure waves generated by the dimensional changes of the active fibres. The muscular sound seems to reflect the intramuscular visco-elastic characteristics and the motor unit activation pattern of a contracting muscle.

Muscular sound and force relationship during isometric contraction in man

In order to validate the use of heart rate (HR) in describing and monitoring physiological demands during soccer activities, the HR versus oxygen uptake ( V(.)O(2)) relationship determined on the field during soccer-specific exercises was compared to that found in the laboratory during treadmill exercise. Seven male amateur soccer players [mean (SE), age 25.3 (1.2) years, body mass 72.9 (2.1) kg, stature 1.76 (0.03) m] performed three trials on the field (two laps of a purpose-made circuit including a variety of soccer activities) at different intensities (moderate, high and very high, according to their rate of perceived exertion) and an incremental test on a treadmill in the laboratory. HR increased linearly with V(.)O(2) during both field and laboratory tests according to exercise intensity ( P<0.01). The mean correlation coefficients of the HR- V(.)O(2) relationships obtained in the laboratory and on the field were 0.984 (0.012) and 0.991 (0.005) ( P<0.001), respectively. The mean value of the HR- V(.)O(2) regression equation slope and intercept obtained in laboratory [0.030 (0.002) and 79.6 (4.6), respectively] were not significantly different compared to those found on the field [0.032 (0.003) and 76.7 (9.7)]. The present study seems to confirm that HR measured during soccer exercises effectively reflects the metabolic expenditure of this activity. Thus, with the aid of laboratory reference tests, the physiological demands of soccer activities can be correctly estimated from HR measured on the field in amateur soccer players.

Arsenio Veicsteinas

Papers

Heart rate variability and autonomic activity at rest and during exercise in various physiological conditions.

Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in man

The surface mechanomyogram as a tool to describe the influence of fatigue on biceps brachii motor unit activation strategy. Historical basis and novel evidence.

Muscular sound and force relationship during isometric contraction in man

Validity of heart rate as an indicator of aerobic demand during soccer activities in amateur soccer players