Gaelic football is one of the major national field sports in Ireland. Similar to other field sports played at high speed and intensity, a significant rate of injury has been observed in gaelic football [
1,
2]. Hamstring injury has been shown to account for approximately 13% of all injuries among gaelic footballers [
3,
4]. A similarly high rate of hamstring injury has also been found among athletes in other sports involving kicking and running, such as Australian rules football [
5]. This rate of injury is highlighted by the amount of match playing time missed by players, with hamstring injury alone resulting in approximately 21 missed player games per club per year in Australian football [
5].
There have been several factors hypothesised to contribute to the risk of hamstring injury. These include inadequate warm-up, fatigue, previous injury, knee muscle weakness or strength imbalance, increasing age, poor movement discrimination, poor flexibility, increased lumbar lordosis and poor running technique [
6‐
8]. While there is emerging evidence that the cause of hamstring injury may be multifactorial [
8,
9], one potential contributing factor which has been much researched is muscle weakness [
10‐
12]. As well as looking at risk factors prospectively [
11], there have been many retrospective trials trying to identify potential deficits present in athletes after hamstring injury [
13‐
15]. The results of these trials have been contradictory and inconsistent. Many retrospective studies, across a variety of sports, have found that athletes with a history of hamstring injury had significantly reduced thigh muscle strength and significant strength imbalance when compared to athletes with no history of hamstring injury [
13,
15,
16]. However, other retrospective studies have found no such relationship between previous hamstring injury and muscle strength [
14,
17]. In addition, in two prospective studies carried out among Australian football players [
11,
12], it was found that those with pre-season muscle weakness and strength imbalance were at a significantly greater risk of sustaining a hamstring strain. These results were, however, directly contradicted by another prospective trial [
10], which found no such association. The reasons for these inconsistencies, in both retrospective and prospective research, are largely unclear. Methodological differences and differences in study populations may explain part of this. It is possible that further sources of confusion are that studies do not all make the same comparisons (within-subject or between-subject), and do not all account for the potential effect of limb dominance affecting the results [
10‐
13].
In addition, strength testing protocols have varied between concentric, isometric and eccentric [
11,
15,
18]. It has been suggested that eccentric hamstring strength may be more sensitive at detecting changes after injury [
15,
19], however the increased risk of injury [
20] is a concern when dealing with previously injured subjects. Therefore, the current study used a more demanding concentric testing protocol than those used in previous studies, to try to avoid the need for eccentric testing.
There has been no previously published research on isokinetic strength after hamstring injury in gaelic footballers, despite the high prevalence of the injury. Most previous studies on gaelic footballers have been primarily concerned with the incidence of injuries [
2,
21,
22]. The aim of this retrospective study was to determine whether significant knee muscle weakness was present among Irish male gaelic football players with a history of hamstring injury. This could help clarify which rehabilitation strategies might be justified in the management of such players, especially since previous hamstring injury is the biggest risk factor for future hamstring injury [
8]. Additional aims were to clarify how any potential changes in muscle strength after injury were best identified and to take into account the potential effect on muscle strength of limb dominance.