Isometric hip and groin strength in elite football players: preliminary investigations into the validity and reliability of testing, comparison to a normal population and in-season strength changes.

Abstract

Hip and groin injuries account for 2-5% of all sporting injuries worldwide. Within elite football they account for 12-16% of all injuries in a season, making them the second most prevalent injury for the sport. Isometric measurement of hip and groin strength is common practice in football and is used in athlete monitoring, injury prevention and rehabilitation protocols. Despite its use, one area yet to be explored fully is the comparison of isometric hip and groin strength in elite-footballers using a new fixed frame dynamometry system. There is also no reference data to understand a ‘normal’ population as a control. Similarly, where this data is used in rehabilitation, there is current a lack of understanding of any variation in isometric strength across a season. The aim of this study is to establish (1) a reliable method to assess hip and groin strength, (2) compare hip and groin strength profiles (dominant and non- dominant maximum adduction and abduction scores, adductor ratios, abductor ratios and adductor:abductor ratios) between elite footballers and a normal population, and (3) explore the variability of isometric hip and groin strength across a season in elite footballers. Study One - Thirty-three participants were recruited to determine the reliability between the KangaTech and HHD using intraclass correlation coefficients. Results showed excellent internal reliability for Kangatech (ICC= L: 0.929 [CI=0.887-0.956]; R: 0.929 [CI=0.886-0.956]) and the HHD (ICC= L: 0.951 [CI=0.920-0.970]; R: 0.931 [CI=0.890-0.957]). Study Two - Twenty-five elite footballer players and sixteen ‘normal’ participants where used to explore differences between the groups’ hip and groin strength profiles. Results showed there was no significant difference between elite football players and a normal population for dominant and non-dominant adduction maximum scores, adduction ratios or abduction ratios. There was a significant difference between elite football player’s and the ‘normal’ population for dominant and non-dominant abduction maximum scores; dominant and non-dominant side adduction:abduction ratios. Study Three - Seasonal variation (June-March) of the elite football player’s hip strength profiles was analysed. This was conducted on a subgroup of seventeen elite football players who had continuous data throughout the season. The season was divided in to three separate time points (TP); TP1- Pre-Season (June), TP2- Mid Season (November), TP 3- Late Season (March). Results from repeated measures ANOVA’s showed no significant time effects on any of elite football players hip strength profiles, except for dominant side adduction:abduction ratios that increased from TP1 to TP3. Although not statistically significant, clinically significant differences were seen in non-dominant adductor maximum scores which increased by 12.5% between timepoint (TP) 1 and TP2 compared to 3% between TP2 and TP3. Dominant maximum adduction scores increased by 18% and 0%, respectively. This research project achieved its aims and established reliable methods of isometric hip strength data measurement in the Kangatech and HHD. Similarities and differences in isometric hip strength profiles between high level elite athletes and a normal population were identified (while obtaining normative values for a normal population) alongside an apparent weakness in the adductor strength of elite football players during pre-season. Therefore, it is recommended that both the KangaTech and HHD can be used to assess isometric hip strength. Considerations should be taken during elite football pre-season return to training protocols due to proposed reduced adductor strength at this time. The use of adductor and abductor ratios of approximately 1 throughout the season is appropriate for monitoring, injury prevention and rehabilitation protocols, however care should be taken when using ratios as variance is observed season throughout the season.