Activity profile of young soccer players during actual match play

This study investigated the activity profile of young soccer players (mean age 11.8 +/- 0.6 years; N = 12) with the aim of providing information for the development of training strategies. Data for movements of each player were obtained using 2 cameras that aimed at the subject throughout the match (Play Controller, Phromos, Italy). Encoders transmitted camera movements to a computer. The collected signals were then converted into distances, times, and speed attained at arbitrarily selected match categories. Players were monitored during official 11 vs. 11 matches (N = 12), with each match consisting of 2 halves, each lasting 30 minutes played on a regular soccer pitch. Mean total match distance amounted to 6,175 +/- 318 m. During the second half, players covered 5.5% less distance (p > 0.05). At speeds between 13.1 and 18.0 km.h(-1), players covered 12% less distance during the second half (p < 0.05). Players stood still 11% of the total time played (3,789 +/- 109 seconds). At speeds faster than 18 km.h(-1), players performed 33 +/- 4 bouts during match play, with a mean time length of 2.3 +/- 0.6 seconds per bout. Mean time interval between two successive maximal sprint bouts was 118.5 +/- 20.5 seconds. Players stood still longer during the course of the second half (229 +/- 76 seconds vs. 173 +/- 61 seconds, p < 0.05). Players tended to play in small areas of the football pitch and spent 9% of the total match time at high intensity. In order to promote a more active space coverage of the young player, at least for the age considered in the present study, the dimensions of the football pitch and the number of players should be reduced.     

Most running demand passages of match play in youth soccer congestion period

The objective of this study was to determine whether there is a decrease in the physical performance of the players in the most demanding passages (MDP) during periods of competition congestion. The study involved 15 under-19 players, belonging to a club in Spain’s first division (age: 18.1 ± 0.8 years, weight: 70.2 ± 4.9 kg and height: 1.78 ± 0.06 m), who were monitored during 23 national and international official matches in the 2018/19 season. The Youth League matches were played between two matches in the national championship in six different weeks. The league matches corresponded to the first 17 matches of the league championship, the period in which the 6 matches in the Youth League were played. The two physical variables analysed were total distance (TD) and distance at > 21 km·h^-1 (TD21). Using the rolling average, four time windows were taken (1, 3, 5 and 10 min), and the values were relativized to the minute (m·min^-1). The main results were that: there were more MDP in the first halves than in the second halves of all the time windows; 2) the central match in the week (Youth League) was the most demanding one; and 3) the players maintained the TD and TD21 in the MDP in the third match compared to the first. The results of this study could provide trainers with information on the need to design training tasks that simulate the demands of competition in relation to the TD and the TD21 according to different time windows.     

The interchangeability of global positioning system and semiautomated video-based performance data during elite soccer match play

In elite-level soccer, player motion characteristics are commonly generated from match play and training situations using semiautomated video analysis systems and global positioning system (GPS) technology, respectively. Before such data are used collectively to quantify global player load, it is necessary to understand both the level of agreement and direction of bias between the systems so that specific interventions can be made based on the reported results. The aim of this report was to compare data derived from both systems for physical match performances. Six elite-level soccer players were analyzed during a competitive match using semiautomated video analysis (ProZone? [PZ]) and GPS (MinimaxX) simultaneously. Total distances (TDs), high speed running (HSR), very high speed running (VHSR), sprinting distance (SPR), and high-intensity running distance (HIR; >4.0 m·s(-1)) were reported in 15-minute match periods. The GPS reported higher values than PZ did for TD (GPS: 1,755.4 ± 245.4 m; PZ: 1,631.3 ± 239.5 m; p < 0.05); PZ reported higher values for SPR and HIR than GPS did (SPR: PZ, 34.1 ± 24.0 m; GPS: 20.3 ± 15.8 m; HIR: PZ, 368.1 ± 129.8 m; GPS: 317.0 ± 92.5 m; p < 0.05). Caution should be exercised when using match-load (PZ) and training-load (GPS) data interchangeably.     

Acid-base balance during repeated cycling sprints in boys and men.

The aim of this study was to investigate the acid-base balance during repeated cycling sprints in children and adults. Eleven boys (9.6 +/- 0.7 yr) and ten men (20.4 +/- 0.8 yr) performed ten 10-s sprints on a cycle ergometer separated by 30-s passive recovery intervals. To measure the time course of lactate ([La]), hydrogen ions ([H(+)]), bicarbonate ions ([HCO(3)(-)]), and base excess concentrations and the arterial partial pressure of CO(2), capillary blood samples were collected at rest and after each sprint. Ventilation and CO(2) output were continuously measured. After the 10th sprint, concentrations of boys vs. men were as follows: [La], 8.5 +/- 2.1 vs. 15.4 +/- 2.0 mmol/l; [H(+)], 43.8 +/- 1.3 vs. 66.9 +/- 9.9 nmol/l (P < 0.001). Significant correlations showed that, for a given [La], [H(+)] was lower in the boys compared with the men (P < 0.001). Significant relationships also indicated that, for a given [La], [HCO(3)(-)] and base excess concentration were similar in the boys compared with the men. Moreover, significant relationships revealed that, for a given [H(+)] or [HCO(3)(-)], arterial partial pressure of CO(2) was lower in the boys compared with the men (P < 0.001). The ventilation-to-CO(2) output ratio was higher in the boys during the first five rest intervals and was then higher in the men during the last five sprints. To conclude, during repeated sprints, the ventilatory regulation related to the change in acid-base balance induced by lactic acidosis was more important during the first rest intervals in the boys compared with the men.     

Acid-base balance during social interactions in rainbow trout (Oncorhynchus mykiss)

Socially subordinate rainbow trout (Oncorhynchus mykiss) experience chronic stress that impacts upon a variety of physiological functions, including Na(+) regulation. Owing to the tight coupling between Na(+) and Cl(-) uptake and, respectively, H(+) and HCO(3)(-) loss at the gill, ionoregulatory changes associated with social status may affect acid-base regulation. The present study assessed the responses of dominant, subordinate and control trout to hypercapnia (1% CO(2)) to test this hypothesis. Social status appeared to impact net acid excretion (J(net)H(+)) as subordinate individuals failed to increase net acid flux in response to hypercapnia. However, blood acid-base status was found to be unaffected by social status before or during hypercapnic exposure, indicating that subordinate fish were as effective as dominant or control trout in achieving compensation for the acid-base disturbance induced by hypercapnic exposure. Compensation in all groups involved decreasing Cl(-) uptake in response to hypercapnia. The branchial activities of both Na(+),K(+)-ATPase (NKA) and V-type H(+)-ATPase were affected by social interactions and/or exposure to hypercapnia. Branchial NKA activity was higher but V-ATPase activity was lower in control fish than in dominant or subordinate trout. In addition, control and subordinate but not dominant trout exposed to 24h of hypercapnia exhibited significantly higher branchial V-ATPase activity than fish maintained in normocapnia. Collectively, the data suggest that subordinate trout are able to regulate blood pH during a respiratory acidosis.     

Acid-base balance and urinary acidification in birds

This essay will treat, first, the defended parameters of acid-base status in avian blood and their modification under conditions pertinent to the life of birds, and, second, urinary acidification and its role in maintenance of acid-base balance. Of the two topics, urinary acidification is of particular interest to the author, has received less sustained attention experimentally and has been infrequently reviewed (Sykes, 1971), so it will receive attention here. The reports cited in the essay concern primarily adult birds outside periods of egg-laying.     

Neuromuscular responses to impact and collision during elite rugby league match play

The purpose of this study was to investigate the relationship between the prematch and short-term postmatch neuromuscular responses to the intensity, number, and distribution of impacts associated with collisions during elite Rugby League match play. Twenty-two elite male Rugby League players were monitored during 8 regular season competition matches using portable global positioning system (GPS) technology. The intensity, number, and distribution of impact forces experienced by players during match play were recorded using integrated accelerometry. Peak rate of force development (PRFD), peak power (PP), and peak force (PF) were measured during a countermovement jump on a force plate 24 hours prematch, 30 minutes prematch, 30 minutes postmatch and then at 24-hour intervals for a period of 5 days postmatch. The change in the dependent variables at each sample collection time was compared with that at 24 hours prematch and 30-minute prematch measures. There were significant (p < 0.05) decreases in PRFD and PP up to 24 hours postmatch with PF significantly (p < 0.05) being decreased 30 minutes postmatch. Significant (p < 0.05) correlations were found between the total number of impacts and PRFD and PP 30 minutes postmatch. Impact zones 4 (7.1-8.0 G), 5 (>8.1-10.0 G), and 6 (>10.1 G) were significantly (p < 0.05) correlated to PRFD and PP 30 minutes postmatch with the number of zone 5 and 6 impacts significantly (p < 0.05) correlated to PRFD and PP 24 hours postmatch. Elite Rugby League match play resulted in significant neuromuscular fatigue and was highly dependent on the number of heavy collisions >7.1G. Results demonstrate that neuromuscular function is compromised for up to 48 hours postmatch indicating that at least 2 days of modified activity is required to achieve full neuromuscular recovery after elite Rugby League match play. Position-specific demands on energy systems and the influence of repeated blunt force trauma during collisions during elite Rugby League match play should be considered when planning postmatch recovery protocols and training activities to optimize subsequent performance.     

Acid-base balance and electrolyte concentration in blood during graded exhausting exercise in non-trained subjects

Venous acid-base balance and electrolyte concentration during step-graded and exhausting exercise with a two-minute steady-state has been studied in a group of non-trained young men. The results showed a significant decrease in pH, pCO2 and bicarbonate and a significant increase in lactate, potassium, inorganic phosphate and proteins during the exercise. The supervening acidosis had a large anion gap that was of proportion with the increase in lactate values. We suggest that the total sum of other anions such as proteins, phosphate, pyruvate, citrate, free fatty acids and aminoacids, as well as sodium-hydrogen exchange could account for this acidosis.     

Intermatch variation of match activity in elite Italian soccer referees

The aim of this study was to examine how match activities, specifically high-intensity activity (HIA; activities performed at speeds faster than 18.1 km x h(-1)), vary among matches in elite soccer referees, because variations in match performance can potentially guide physical conditioning regimens for these referees. Fourteen Italian soccer referees were observed during 65 first-division matches a minimum of 3 and a maximum of 6 times each. For comparison, shorter matches (SM) and longer matches (LM) for each referee were identified. Mean (+/-SD) SM and LM total distances were 10,949 +/- 1,095 m and 12,303 +/- 666 m (p < 0.001), respectively. SM and LM were not different in term of duration (p > 0.05). During LM, referees spent 44% less time standing still (p < 0.01) and covered 10% more distance at low intensity than they did in SM (p < 0.05). No HIA variation was observed between SM and LM (p > 0.05). For the elite referee, work rate is increased without affecting HIA.     

Acid-base balance and plasma glutamine concentration in man

Plasma glutamine concentrations were measured in chronic metabolic acidosis and alkalosis in healthy male volunteers. Metabolic acidosis resulted in a significant drop in glutamine concentration while metabolic alkalosis significantly elevated glutamine levels. These changes in glutamine concentration correlated with both the bicarbonate and PCO2 levels. To determine whether bicarbonate or PCO2 levels influence the glutamine concentrations, respectively acidosis was induced by respiring 5% CO2. This resulted in a significant elevation in both PCO2 and glutamine while bicarbonate levels remained unchanged. The results demonstrate an effect of acid-base alterations upon plasma glutamine concentration mediated by PCO2.     

Individual match playing time during the season affects fitness-related parameters of male professional soccer players

The purpose of this study was to analyze the effects of an entire season on physical fitness parameters (PFPs) in male professional soccer players (N = 18). Performance in 5- and 30-m sprint (T5 and T30), countermovement jump (CMJ), agility (T-test), knee extensor (KE) and knee flexor (KF) isokinetic strength, hamstrings/quadriceps strength ratio (H/Q) and bilateral differences (BDs), and Yo-Yo intermittent endurance test 2 (YYIE2) was evaluated in 4 moments (E1-E4) throughout the season. Individual match playing time was quantified. Significant improvements in CMJ and YYIE2 from E1 to E2 were observed (p < 0.05-0.01). The T30 improved from E2 to E3 (p < 0.01). The CMJ decreased from E2 to E3 and E4, and YYIE2 from E2 to E4 (p < 0.05). There were increments in the H/Q ratio and Agility from E1 and E2 to E3 and E4 (p < 0.05-0.01). Significant correlations were found in all evaluation points between different PFPs and between changes in strength parameters and agility, T5 and T30, CMJ, and YYIE2 (p < 0.05-0.001). Influence of individual match playing time was correlated to changes in T5 (E1 to E3; r = -0.705), KE nondominant leg (KEND; E2 to E3; r = 0.786), and KF (E3 to E4; r = 0.575-0.590). The interrelationship between muscle strength (e.g., KE), sprint (e.g., T5), and jump abilities (CMJ) suggests the importance of muscle strength and power training for soccer. This study suggests that the systematic participation of the players in soccer matches favors the increase and maintenance of soccer players KE and KF muscle strength and sprint ability (T5). Thus, given the unique demands of actual match play, coaches should try to incorporate a competitive friendly match in the weekly training cycle of nonstarter players.     

Biochemical and endocrine responses to impact and collision during elite Rugby League match play

The purpose of this study was to investigate the relationship between the prematch and short-term postmatch biochemical and endocrine responses to the intensity, number, and distribution of impacts associated with collisions during elite Rugby League match play. Seventeen elite male Rugby League players each provided blood and saliva samples 24 hours prematch, 30 minutes prematch, 30 minutes postmatch, and then at 24-hour intervals for a period of 5 days postmatch to determine plasma creatine kinase concentration ([CK]) and salivary cortisol concentration ([sCort]). The intensity, number, and distribution of impact forces experienced by players during match play were recorded using portable global positioning systems (GPSs). The change in the dependent variables at each sample collection time was compared to 24 hours prematch and 30-minute prematch measures. The [CK] and [sCort] increased significantly (p < 0.05) during match play. Significant correlations (p < 0.05) were observed between the number of hit-ups and peak [CK] 24 hours postmatch, 48 hours postmatch, and 72 hours postmatch (p < 0.05). The number of impacts recorded in zone 5 (8.1-10.0G) and zone 6 (>10.1G) during match play was significantly correlated (p < 0.05) to [CK] 30 minutes postmatch, 24 hours post, 48 hours post, and 72 hours postmatch. The GPS was able to provide data on the intensity, number, and distribution of impacts resulting from collisions during match play. Elite Rugby League match play resulted in significant skeletal muscle damage and was highly dependent on the number of heavy collisions >8.1G. [CK] remained elevated 120 hours postmatch identifying that at least 5 days modified activity is required to achieve full recovery after elite Rugby League match play.     

Bone growth and calcium balance during simulated weightlessness in the rat

Rats, age 28 days, experiencing tail suspension in modified metabolic cages for 1, 2, and 3 wk were compared with littermate controls. Food and water consumption, urinary and fecal Ca excretion, and serum Ca were measured; hearts, fore- and hindlimb bones, skulls, and mandibles were removed for determination of wet, dry, and ash weights and Ca concentration and for histological examination. Weight gain and Ca intake and excretion were the same for both groups; both displayed net Ca gain. Suspended rats had significantly lower wet, dry, and ash weights of femora and tibiae. Dry weights of the humeri and radii/ulnae were moderately higher, and the skull and mandible dry and ash weights were significantly higher in suspended than in control rats. Cortical thickness of the femur, but not humerus, was less in suspended rats. The data are consistent with the hypothesis that bone growth is influenced by the cardiovascular changes associated with tail suspension.     

Unilateral balance performance in female collegiate soccer athletes

The Star Excursion Balance Test (SEBT) is a unilateral balance task designed to evaluate dynamic postural control. This investigation explored the relationship between limb preference, strength, and performance on the SEBT in NCAA Division I, female collegiate soccer athletes (nonsoccer, n = 11; soccer, n = 12). Each participant completed maximal, concentric test efforts at a velocity of 90 degrees x s(-1) for supine ankle dorsiflexion (ADF) and plantarflexion (APF) and at 60 degrees x s(-1) for the seated leg extension (LE) and flexion (LF) and supine hip extension (HE) and flexion (HF). In addition, participants performed maximal SEBT reaches in the anterior, medial, and posterior directions. All testing was completed on both limbs. These results indicate that SEBT performance is similar for both limbs in both groups. The soccer group, however, reached significantly farther than the nonsoccer group, suggesting that the SEBT may be sensitive to training status and/or sport-related adaptations. The concentric strength results indicate that despite group differences in all strength tests, strength in general was not highly correlated to SEBT performance. Thus, neuromuscular factors above and beyond strength may have accounted for the group differences in SEBT performance. The SEBT may be a useful tool for determining the relative effectiveness of an intervention designed to improve postural control.