Lower preseason reactive strength index scores are associated with injury in female collegiate volleyball players but not male collegiate basketball players

ObjectivesFunctional tests are used by sports medicine professionals to discriminate injury risk in athletes. One test that has shown promise is the drop vertical jump (DVJ); however, it is primarily used to evaluate measures associated with anterior cruciate ligament injury. The DVJ test can also be used to calculate the reactive strength index (RSI); a measure used to assess an athlete’s power. The ability of the RSI to discriminate injury risk is unknown. The purpose of this study was to prospectively evaluate the ability of preseason RSI scores to identify athletes at risk for a noncontact time-loss injury to the low back or lower extremities.DesignProspective cohort.MethodsOne hundred and fifty-five male collegiate basketball (BB) players and 117 female collegiate volleyball (VB) players were recruited for this study. DVJ tests were performed in a motion capture lab.ResultsFemale VB players with a RSI 0.9125 m/s or less (30.48 cm box) were 4 times (relative risk = 4.2 [95% CI: 1.0, 17.7]; p-value = 0.024) more likely to be injured. There was no association between preseason scores and injury in the male BB athletes.ConclusionRSI scores should be collected for female collegiate VB players as part of a preseason screen.     

The incidence and characteristics of purposeful heading in male and female youth football (soccer) within Australia

ObjectivesTo quantify the incidence and characteristics of purposeful headers and unintentional head impacts during male and female youth football (soccer) games in Australia.DesignCross-sectional observational study.MethodsTen match-videos (total n = 110) per playing age (under 13–20 males; under 13–17 females) from the 2019 National Premier League season were coded for purposeful headers and unintentional head impacts. Total headers and head impacts as well as incidence rate (IR) per 1000 match-hours for different match characteristics were calculated.ResultsPurposeful headers accounted for 99% (n = 4615, IR:1618) of total head impacts. The IR of purposeful headers per 1000 match-hours was highest for under-15 males (IR:2117) and under-17 females (IR:2090) followed by under-20 males (IR:1761). Midfielders completed the most headers in all female age groups (mean IR:713) and under 13–14 males (mean IR:891), with defenders completing the most headers in under 15–20 males (mean IR:760). Heading duels accounted for 16% of total headers with most headers performed during free play (68%), throw-ins (15%), free kicks (12%) and corner kicks (5%). Only 57 head impacts (IR:20) were coded as unintentional head impacts resulting from being struck by the ball or opponent body part with 4 (IR:1.4) requiring medical attention.ConclusionsHeading is a complex skill. Given the propensity of youth players of all ages to purposefully head the ball, consideration should be given to coaching heading technique based on specific game scenarios for their playing position and age group. The findings of this study can be used to inform heading guidelines.     

Motor performance is not related to injury risk in growing elite-level male youth football players. A causal inference approach to injury risk assessment

ObjectiveTo identify the causal relation between growth velocity and injury in elite-level youth football players, and to assess the mediating effects of motor performance in this causal pathway.DesignProspective cohort study.MethodsWe measured the body height of 378 male elite-level football players of the U13 to U15 age categories three to four months before and at the start of the competitive season. At the start of the season, players also performed a motor performance test battery, including motor coordination (Körperkoordinationstest für Kinder), muscular performance (standing broad jump, counter movement jump), flexibility (sit and reach), and endurance measures (YoYo intermittent recovery test). Injuries were continuously registered by the academies’ medical staff during the first two months of the season. Based on the causal directed acyclic graph (DAG) that identified our assumptions about causal relations between growth velocity (standardized to cm/y), injuries, and motor performance, the causal effect of growth velocity on injury was obtained by conditioning on maturity offset. We determined the natural indirect effects of growth velocity on injury mediated through motor performance.ResultsIn total, 105 players sustained an injury. Odds ratios (OR) showed a 15% increase in injury risk per centimetre/year of growth velocity (1.15, 95%CI: 1.05–1.26). There was no causal effect of growth on injury through the motor performance mediated pathways (all ORs were close to 1.0 with narrow 95%CIs).ConclusionsGrowth velocity is causally related to injury risk in elite-level youth football players, but motor performance does not mediate this relation.     

Effect of motivational climate on sportspersonship among competitive youth male and female football players

The purpose of this study was to investigate the influence of perceived motivational climate and gender on sportspersonship behavior of competitive youth football players. Participants were 512 boy and 202 girl Norwegian youth football players (12-14 years old) competing in an international football tournament. A 2 x 2 x 2 (gender, mastery climate high and low, performance climate high and low) MANOVA produced no multivariate or interaction effects, but main effects for gender, performance climate, and mastery climate did emerge. Post hoc analyses of the simple main effects found that boys and girls were different in sportspersonship, but only in that boys were more sportspersonlike than girls on one of the four sportspersonship dimensions. Players perceiving a high mastery climate endorsed sportspersonship more than those players perceiving a low mastery climate, and players perceiving a high performance climate were less likely to endorse sportspersonship than players perceiving a low performance climate. Canonical correlation analysis revealed that a strong mastery climate was positively associated with commitment, respect for social conventions, and respect for rules and officials. A strong performance climate was negatively associated with respect and concern for social conventions and respect for rules and officials, while a positive association emerged for respect and concern for the opponent. The results of our study suggest that both boys and girls may well perceive the coach emphasizing similar criteria of success and failure and thereby a similar culture of sportspersonship, while in general a strong mastery climate leads to a higher sportspersonship orientation.     

Post-match recovery of eccentric knee flexor strength in male professional football players

ObjectivesThis study aimed at verifying the effect of a football match on the eccentric knee flexor strength of male professional players along a 72-h period.Study designQuasi-experimental study.SettingFootball club facilities.ParticipantsFifteen players were assessed in four timepoints: 24 h before, immediately after, 48 h and 72 h after the match.Main outcome measuresThe eccentric knee flexor strength was assessed during the Nordic hamstring exercise execution.ResultsPlayers presented a significant strength reduction immediately after match (Δ = 12%; p = 0.001; large effect size, d = 1.10), and did not recover their strength capacity within a 48 h-period (Δ = 6%; p = 0.011; moderate effect size, d = 0.57). At 72 h after the match, strength was similar to baseline levels (Δ = 3.5%; p = 0.122; small effect size, d = 0.34). Secondarily, individual response analysis considered a player ‘fully recovered’ when his strength deficit compared to the baseline measure was lower than the measurement coefficient of variation (i.e., <5%). Only 6 (40%) and 9 (60%) players were ‘fully recovered’ at 48 h and 72 h after the match, respectively.ConclusionProfessional football players experienced an immediately post-match drop on the eccentric knee flexor strength, and significant strength deficits persisted for a 48-h period. Some players were not recovered at 72 h after the match.     

Injuries among male and female elite football players

All 12 female football clubs (228 players) and 11 of 14 male clubs (239 players) in the Swedish premier league were followed prospectively during the 2005 season. Individual exposure (playing time), injuries (time loss), and injury severity (days lost due to injury) were recorded by the team medical staffs. Injury incidence was higher for male players during both training (4.7 vs 3.8 injuries/1000 h, P=0.018) and match play (28.1 vs 16.1, P<0.001). However, no difference was found in the incidence of severe injury (absence >4 weeks) (0.7/1000 h in both groups). The thigh, especially the hamstrings, was the overall most commonly injured region in both sexes, while the hip/groin was more commonly injured in male players and the knee in female players. Knee ligament injuries accounted for 31% and 37% of the total time lost from football for male and female players, respectively. In conclusion, male elite players had a higher injury incidence than their female counterparts although no difference was observed in the incidence of moderate to severe injury. We recommend that preventive measures should be focused on hamstring and knee ligament injury in order to reduce the overall injury burden.     

Normative values and changes in range of motion,strength, and functional performance over 1 year in adolescent female football players: Data from 418 players in the Karolinska football Injury Cohort study

ObjectiveTo study normative values of range of motion (ROM), strength, and functional performance and investigate changes over 1 year in adolescent female football players.DesignCross-sectional.Participants418 adolescent female football players aged 12–17 years.Main outcome measuresThe physical characteristic assessments included (1) ROM assessment of the trunk, hips, and ankles; (2) strength measures (maximal isometric and eccentric strength for the trunk, hips, and knees, and strength endurance for the neck, back, trunk and calves), and (3) functional performance (the one-leg long box jump test and the square hop test).ResultsOlder players were stronger, but not when normalized to body weight. Only small differences in ROM regarding age were found. ROM increased over 1 year in most measurements with the largest change in hip external rotation, which increased by 6–7° (Cohen's d = 0.83–0.87). Hip (d = 0.28–1.07) and knee (d = 0.38–0.53) muscle strength and the square hop test (d = 0.71–0.99) improved over 1 year.ConclusionsNormative values for ROM and strength assessments of neck, back, trunk, hips, knees, calves and ankles are presented for adolescent female football players. Generally, fluctuations in ROM were small with little clinical meaning, whereas strength improved over 1 year.     

Health problems in former elite female football players: Prevalence and risk factors

The aim of this study was to assess the prevalence of health problems and associated risk factors in former elite female football players. A cross‐sectional research design was employed, using an online questionnaire on personal characteristics and health complaints during/after the career. One hundred fifty‐two (response rate: 62.0%) former first German league players answered the survey. Around 70% described their current health as good or very good. Over half (57.9%) reported knee problems during the last 4 weeks while exercising and a third (33.6%) during normal daily activities. The second most common location for complaints was the head (53.3%). Almost one quarter (23.7%) of players suffered from osteoarthritis (OA). Regression analysis showed that OA in knee/ankle and physical complaints (PC) in knee/ankle/head were significantly predicted by number and severity of previous injuries (P < 0.05). Further, increases in age, training volume, and level of play were associated with an increased likelihood of presenting with OA (P < 0.05), but not PC. In conclusion, a football career may lead to specific long‐term health problems in elite female players. Prevention strategies should focus on knee, ankle, and head injuries. Future studies are needed to clinically assess the prevalence rates of OA and possible neurocognitive changes.     

The acute effect of match play on hamstring strength and lower limb flexibility in elite youth football players

The aim of this study was to investigate the effect of competitive football match play on hamstring strength and lower limb flexibility. Fifteen male international youth football players were included. Hamstring strength and associated pain ratings, ankle dorsiflexion, hip extension, knee extension and flexion range of motion were evaluated immediately post‐match and at intervals of 24, 48, and 72 h post‐match. Strength significantly reduced post‐match (P < 0.01), mean difference ?0.43 (CI₉₅: ?0.56, ?0.30) and 24 h post (P < 0.05) mean difference ?0.12 Nm/kg (CI₉₅: ?0.20, ?0.04). The associated pain scores significantly increased at the post‐match (P < 0.01, ES = 0.61) and 24 h (P < 0.01, ES = 0.55) time intervals. At the 48 and 72 h post‐match tests no significant difference was found for strength or pain ratings. No significant differences were detected for any of the range of motion measures. Competitive football match play has a significant acute and transient effect on isometric hamstring strength and associated pain levels during resisted knee flexion in male international youth players. Range of motion measures appear to remain relatively unaffected by match play. Isometric hamstring strength testing and associated pain levels might be considered for inclusion in‐season to monitor player's post‐match hamstring recovery characteristics.     

Does kinesiology taping of the ankles affect proprioceptive control in professional football (soccer) players?

ObjectiveTo determine whether the bilateral application of kinesiology tape (KT) to professional footballers' ankles can improve their lower limb proprioception.DesignA single blind randomised crossover study. Participants were randomly assigned to complete a proprioception test in either a taped or not taped condition first. Following a wash out period, participants were then re-tested in the alternate condition.SettingA UK Championship League Football Club, mid-season.ParticipantsTwenty male professional football players over the age of 18, currently match fit with no injuries.Outcome measureProprioception was assessed by participants undertaking the moving target program on the balance module attached to a Kin-Com 125AP isokinetic dynamometer. A paired sample two tailed t-test was used to assess whether there was a significant difference between the participants test scores in the not taped and taped conditions.ResultsThe bilateral application of KT to professional footballers' ankles did not bring about a significant change in participants' scores when tested with a fine movement and balance control test. Percentage accuracy score mean difference 4.2 (p = 0.285).ConclusionThe results of this study do not support the use of KT when applied to the ankles of healthy footballers as a method of improving proprioception.     

Prevalence of sport specialisation and association with injury history in youth football

ObjectivesThe aims of this study were to determine the prevalence of sport specialisation in youth football, and to investigate the associations of sport specialisation and volume of sport participation with injury history.DesignCross-sectional questionnaire.SettingNew Zealand youth football teams.Participants414 youth football players aged 10–15 years.Main outcome measuresThe level of specialisation, average weekly sport participation and free-play volume were recorded. 12-month injury history was captured and grouped by injury type. Associations between level of specialisation and demographic variables were analysed using chi square tests. Logistic regression was used to investigate associations between injury history, level of specialisation, and volume of participation.ResultsParticipants were classified as high (43%), moderate (38%), or low (19%) specialised (n = 399 complete). High specialisation was more likely in boys, older participants, and those from large schools. Highly specialised participants were more likely to report a history of gradual onset injury than those who were low specialised (n = 340 with complete injury data). Odds of reporting a gradual onset injury also increased with greater weekly and annual sport participation volume.ConclusionsThere is a high prevalence of sport specialisation in youth football, and it is associated with increased incidence of gradual onset injury.     

Stress fractures in elite male football players

The objective was to investigate the incidence, type and distribution of stress fractures in professional male football players. Fifty‐four football teams, comprising 2379 players, were followed prospectively for 189 team seasons during the years 2001–2009. Team medical staff recorded individual player exposure and time‐loss injuries. The first team squads of 24 clubs selected by UEFA as belonging to the 50 best European teams, 15 teams of the Swedish Super League and 15 teams playing their home matches on artificial turf pitches were included. In total, 51 stress fractures occurred during 1 180 000 h of exposure, giving an injury incidence of 0.04 injuries/1000 h. A team of 25 players can therefore expect one stress fracture every third season. All fractures affected the lower extremities and 78% the fifth metatarsal bone. Stress fractures to the fifth metatarsal bone, tibia or pelvis caused absences of 3–5 months. Twenty‐nine percent of the stress fractures were re‐injuries. Players that sustained stress fractures were significantly younger than those that did not. Stress fractures are rare in men's professional football but cause long absences. Younger age and intensive pre‐season training appear to be risk factors.     

Reliability of handheld dynamometry in assessment of hip strength in adult male football players

The aim of this study was to evaluate the intra- and interrater reliability of handheld dynamometry (HHD) for measuring hip muscle strength in a sample of 30 healthy semi-professional adult male football players. The reliability of HHD had not been assessed in athletes who were likely to be stronger than populations tested previously. Maximal isometric strength of resisted hip flexion and adduction were measured. Mean strength ranged from 51.5 kg for dominant hip flexion to 26.7 kg for hip adduction at 90° of hip flexion. Intrarater reliability intraclass correlation coefficients (ICCs) ranged from 0.70 to 0.89. ICCs for interrater reliability ranged from 0.66 to 0.87. As expected, muscle strength in this group of athletes was significantly higher than that of populations in which HHD reliability has been assessed. Despite this, muscle strength testing of hip flexor and adductor muscles can be performed with good to excellent intra- and interrater reliability in this population.     

Neuromuscular fatigue and recovery in elite female handball players

The purpose of this study was to investigate the degree of neuromuscular fatigue and recovery from fatigue, following handball training and handball matches at elite level. The focus was specifically on changes in physical performance when playing three matches over the course of 3 days, which simulates a sequence in international championships. Female players from the Norwegian national handball team were tested during a 5-day training camp (seven players) and a 3-day international tournament (eight players). Testing was done before and after training sessions and matches. Neuromuscular fatigue was measured as changes in voluntary isokinetic knee extensions, jump height in counter-movement jumps, and 20 m sprint time. The results showed a significant reduction by 2-6% in all three performance tests during the training camp and by 4-7% during the tournament (sprint and jump test) (P<0.05). Slow recovery was indicated by incomplete restoration of performance between matches and training sessions. The paper discusses the insufficient recovery measured related to handball performance. Because of changes in the rules of the game and strategic tendencies towards higher speed in play, the physical demands in elite handball seems to be increasing. The results of the study indicate that coaches should consider physical loading and recovery time available when distributing playing time between individual players in international tournaments.     

Explosive strength in female 11-on-11 versus 7-on-7 soccer players

Lower limbs strength capacity in female soccer players is poorly addressed. The aim of this study was to evaluate explosive strength in 7-on-7 (7FP) and 11-on-11 (11FP) female players and its possible changes at 3 different checkpoints of the competitive season. Thirteen 11FP of mean age 22.0 years) and twenty-six 7FP (of mean age 23.6 years) were enrolled. Vertical jump capacity was determined by means of squat jump (SJ) and counter movement jump (CMJ) tests in 3 different periods (September 2005, December 2005, April 2006). No significant differences were observed in SJ elevation or CMJ elevation between the two groups at any time point, and there were no significant changes over time. However, 7FPs tended to have higher explosive performance during SJ compared to 11FPs, and they had a significantly lower elastic recoil index at all three evaluations. This may be due to the characteristics of 7-on-7 soccer, in which the neuromuscular and explosive strength demands are higher than those of 11-on-11 soccer. Such requirements, though increasing muscular explosive performance, also increase the rigidity of the lower limb extensor apparatus.     

Using machine learning to improve our understanding of injury risk and prediction in elite male youth football players

ObjectivesThe purpose of this study was to examine whether the use of machine learning improved the ability of a neuromuscular screen to identify injury risk factors in elite male youth football players.DesignProspective cohort study.Methods355 elite youth football players aged 10–18 years old completed a prospective pre-season neuromuscular screen that included anthropometric measures of size, as well as single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), 75% hop distance and stick (75%Hop), Y-balance anterior reach and tuck jump assessment. Injury incidence was monitored over one competitive season. Risk profiling was assessed using traditional regression analyses and compared to supervised machine learning algorithms constructed using decision trees.ResultsUsing continuous data, multivariate logistic analysis identified SLCMJ asymmetry as the sole significant predictor of injury (OR 0.94, 0.92–0.97, p < 0.001), with a specificity of 97.7% and sensitivity of 15.2% giving an AUC of 0.661. The best performing decision tree model provided a specificity of 74.2% and sensitivity of 55.6% with an AUC of 0.663. All variables contributed to the final machine model, with asymmetry in the SLCMJ, 75%Hop and Y-balance, plus tuck jump knee valgus and anthropometrics being the most frequent contributors.ConclusionsAlthough both statistical methods reported similar accuracy, logistic regression provided very low sensitivity and only identified a single neuromuscular injury risk factor. The machine learning model provided much improved sensitivity to predict injury and identified interactions of asymmetry, knee valgus angle and body size as contributing factors to an injurious profile in youth football players.     

Comparison of injuries sustained on artificial turf and grass by male and female elite football players

The objective of this study was to compare incidences and patterns of injury for female and male elite teams when playing football on artificial turf and grass. Twenty teams (15 male, 5 female) playing home matches on third‐generation artificial turf were followed prospectively; their injury risk when playing on artificial turf pitches was compared with the risk when playing on grass. Individual exposure, injuries (time loss) and injury severity were recorded by the team medical staff. In total, 2105 injuries were recorded during 246 000 h of exposure to football. Seventy‐one percent of the injuries were traumatic and 29% overuse injuries. There were no significant differences in the nature of overuse injuries recorded on artificial turf and grass for either men or women. The incidence (injuries/1000 player‐hours) of acute (traumatic) injuries did not differ significantly between artificial turf and grass, for men (match 22.4 v 21.7; RR 1.0 (95% CI 0.9–1.2); training 3.5 v 3.5; RR 1.0 (0.8–1.2)) or women [match 14.9 v 12.5; RR 1.2 (0.8–1.8); training 2.9 v 2.8; RR 1.0 (0.6–1.7)]. During matches, men were less likely to sustain a quadriceps strain (P=0.031) and more likely to sustain an ankle sprain (P=0.040) on artificial turf.     

Normative values of hip strength in adult male association football players assessed by handheld dynamometry

Chronic groin pain is a common problem in association football players. Normative values for the strength of hip muscles, measured in an accurate and accessible manner, are needed to gauge strength and inform return to play decisions in this group. The purpose of this study was to define normative values of hip muscle strength using handheld dynamometry. A series of reliable clinical tests that are commonly used when making return to sport decisions in athletes with chronic adductor related groin pain have been selected. One hundred and twenty adult male association football players, free from injury, were recruited. Isometric strength of the hip flexors and adductor muscles was measured using a handheld dynamometer. Mean age was 24.9 years (SD 5.9). Eighty participants (67%) had experienced groin pain in the past. Mean strength for dominant leg hip flexion was 47.3 kg (95% confidence interval 45.6–49.0), non-dominant leg hip flexion was 42.5 kg (41.1–43.9), adduction at 0° hip flexion was 35.6 kg (34.1–37.1), adduction at 45° was 32.0 kg (30.9–33.1), and adduction at 90° was 25.5 kg (24.4–26.5). This study establishes reference ranges and predictive equations for maximal isometric contraction strength of the hip muscles in non-injured adult male association football players. This information will assist assessment and management of an athlete's return to play following injury.