The 31st Olympiad, this year’s biggest sporting event, has successfully closed in Rio de Janeiro, Brazil. Football, or soccer, the most popular, followed, and influential sport in Brazil, was quick to gather a huge international audience for the event. In celebration of this event, Research in Sports Medicine is launching a special fourth issue for 2016. This issue focuses on training, performance and injuries in football.
This issue features 12 articles, eight of which discuss football training and performance and the rest on injuries. Ten of the articles are supported by original research, and the remaining two are short communication articles. The articles were submitted by contributors from Spain, Italy, Greece, Portugal, Tunisia, Germany and the United States.
The issue starts with an article entitled ‘Effects of horizontal plyometric training volume on soccer player’s performance.’ This article examines the dose–response effect of strength and conditioning programs involving horizontally oriented plyometric exercises for relevant soccer performance variables. The authors found that horizontal plyometric training can effectively improve injury-prevention variables. This article indicates that increased volume of horizontal plyometric training has no additional effect on the functional aspects of soccer players’ performance.
Repeated sprint ability protocols are commonly used as testing and training tools in football. The second article, ‘The effect of slope on repeated sprint ability in young soccer players,’ suggests that repeated sprint ability (RSA) protocol is performed with less fatigue and fewer negative effects on running mechanics when it is performed on a slope surface than on a level field. A gradient RSA protocol could allow players to engage in increased RSA training to obtain benefits on running mechanics.
The title of the third article is ‘Agility profile in sub-elite under-11 soccer players: Can SAQ training adequately improve sprint, change of direction speed, and reactive agility performance?’. The authors examined the effects of a 12-week speed, agility and quickness (SAQ) training on acceleration, change of direction speed and reactive agility in sub-elite under-11 soccer players. Their findings showed that the SAQ training program can significantly improve acceleration over short distances and reactive agility in preadolescent soccer players.
The fourth article, ‘Who run the fastest? Anthropometric and physiological correlates of 20 m sprint performance in male soccer players,’ considered the importance of sprint performance in soccer and examined the correlates of sprint performance among a large sample of soccer players. This article compared the players’ anthropometric and physiological characteristics when performing different sprint tasks using cycle ergometer. The magnitude of correlations of sprint time with measures of lower limbs muscle strength and power was larger than with anthropometric measures.
The fifth article entitled ‘Physical and technical performances are not associated with tactical prominence in U14 soccer matches’ analyzed the association between physical or technical variables and tactical prominence variables in under-14 football players. They found a positive and moderate correlation between dribbling test and betweenness centrality, and a negative moderate correlation between % fatigue index and betweenness centrality.
Intermittent running ability is one of the most important physical factors in football. The sixth article entitled ‘The specificity of the Loughborough Intermittent Shuttle Test for recreational soccer players is independent of their intermittent running ability’ investigated whether or not recreational soccer players and non-soccer players with similar intermittent running ability have similar physiological responses to a soccer match simulation protocol. The results of this study challenge the assumption of intermittent running ability as the main determinant of physical performance in soccer players.
The psychophysical state of professional soccer players may change depending on training load. In the seventh article ‘Changes of the psychophysical state and feeling of wellness of professional soccer players during pre-season and in-season periods’, the authors used the Hooper questionnaire to evaluate the intensity of pre-season training load and the psychological influence of reduced frequency and duration in preserving player intensity in-season.
The eighth article is entitled ‘Relationship between daily training load and psychometric status of professional soccer players’. The Hooper questionnaire was also used in this study to observe the relationship between daily training load experiences among soccer players. This study suggested that perceived sleep, stress, fatigue and muscle soreness are moderately related to the daily training load of professional soccer players.
Four articles on football injury were also published. The first article on injury for this issue’s segment is entitled ‘Risk assessment of back pain in youth soccer players’. Contributors adopted a cross-sectional design and used a survey to assess the prevalence of back pain in adolescent soccer players of Bavaria aged 12–19 years. They identified the potential developmental risk factors of these symptoms. The authors obtained data from 1,110 athletes and found 15 factors that influence the appearance of pain. These factors are integrated into a feasible nomogram.
The 10th article, ‘Reducing purposeful headers from goal kicks and punts may reduce cumulative exposure to head acceleration’, compared peak linear and rotational head acceleration across different strategic soccer heading scenarios. Strategic scenarios included bounce, secondary header, punt, throw-in, goal kick, corner kick and kick. Goal kicks and punts result in linear and rotational head accelerations that are higher than the base variable kick. This study suggested that limiting headers to goal kicks and punts in younger athletes who are still learning proper heading techniques may limit cumulative linear and rotational accelerations.
The long-term effects of repetitive head impacts due to heading are an area of increasing concern. Exposure to such impacts must be assessed. The 11th article in this issue, entitled ‘Validation and calibration of HeadCount, a self-report measure for quantifying heading exposure in soccer players’, validated HeadCount, which is a 2-week recall questionnaire. Calibration analysis demonstrated that men tend to report heading accurately, whereas women tend to report overestimated assessments. HeadCount is a valid instrument for tracking heading behavior, but the authors found the need for necessary calibrations for women.
The special issue ends with an article that introduces ‘Epidemiology of football injuries in the 2012/2013 and 2013/2014 seasons of the Italian Serie A’. The authors collected data from a free collaborative international database. They identified 363 football-related injuries occurred throughout the two seasons. The most commonly reported injuries were thigh-strain and knee injuries. Injury incidence increased with age and was particularly high from August to October. The authors suggest that injury prevention strategies should be introduced during the pre-season to reduce risks, especially on muscle strains.
All contributions to this issue are original research articles. We hope that this issue will add to the knowledge of football and bridge the gap between science and practice. The Editorial Board expresses deep appreciation for the authors of this issue.