Australian Rules Football is played in Australia at both community and professional levels. During the last 10 AFL playing seasons (2001–2010), injuries grouped as “hip, thigh, and groin” have consistently had the highest incidence (12.6% incidence of new injuries per club for 10 yr), prevalence (44.8% of missed games per club for 10 yr), and recurrence rate (62% recurrent injuries as a percentage of new injuries for 10 yr) of all injury groups (30). In addition, despite the latest advances in exercise physiology and sports medicine, both the incidence and prevalence rates of injuries classified as “trunk/back” in the AFL injury report have remained constant (30). Efforts to reduce the injury rates have largely been directed toward changes in the rules for playing the game and in training regimes. Few initiatives have targeted the trunk musculature that links to the lower limb kinetic chain where these injuries predominantly occur.
Many factors contribute to the injuries incurred by AFL players. One factor that has been considered is the presence of atrophy and side-to-side asymmetry in the muscles of the lumbopelvic and trunk region. The repetitive use of a dominant limb in many sports, including AFL, can result in the hypertrophy of muscles and, consequently, cause asymmetries across sides (26,28). The quadratus lumborum and psoas major muscles are known to be asymmetrical among many cricket and AFL players (14,17,33). Furthermore, Engstrom et al. (11) linked asymmetry of the quadratus lumborum muscle in cricket fast bowlers with lumbar spine injury.
Injuries may also be linked to poor motor control. Stability of the lumbopelvic region involves good dynamic neuromuscular control and intact passive structures (40). This stability aids in the production, transfer and control of force, and movement to and from distal segments in the kinetic chain (27). Deficits in either passive or dynamic structures within the lumbopelvic region may potentially cause injury within any segment of the kinetic chain (27). Prospective studies that have investigated neuromuscular control of the trunk have shown that deficits in this area can predict lower limb injuries (41,42). Zazulak et al. (41) showed that increased trunk displacement in response to sudden trunk force release (factors related to lumbopelvic stability) was predictive of knee and anterior cruciate ligament injuries in athletes. The rationale for this was that decreased neuromuscular control of the trunk, coupled with high ground reaction forces directed toward the body’s center of mass, compromised the dynamic stability of the knee joint and increased knee injury risk. The conclusion of the study was that measurable deficits in trunk control may identify athletes at increased risk of injury. Although all trunk muscles may contribute to the control of stability of the spine and pelvis, there is evidence that muscles such as the transversus abdominis and multifidus play an important role.
The multifidus muscle contributes to localized control of segments of the lumbar spine and controls the lumbar lordosis (5,39), which plays a crucial role in force distribution from the lower limbs. Loss of neuromuscular control of the multifidus muscle due to fatigue or injury could therefore disrupt the integrity of the kinetic chain. Impairments of this muscle have been documented in subjects with low back pain (LBP), as well as among AFL players. There is evidence that the cross-sectional area (CSA) of the multifidus muscle is selectively decreased compared to other lumbopelvic muscles in patients with chronic LBP (9). Researchers have used real-time ultrasound imaging to demonstrate segmental decrease in CSA of the multifidus muscle ipsilateral to painful symptoms, in patients with acute unilateral LBP (22). A similar localized (rather than generalized) pattern of atrophy has been demonstrated in subjects with chronic unilateral LBP (15). However, among AFL players, decrease in the multifidus muscle CSA can also be a response to playing football (16). Furthermore, a small CSA of the multifidus muscle at the lumbosacral junction was predictive of relatively more severe lower limb injuries among this elite group of AFL players (20), indicating that interventions to increase multifidus muscle size could have a positive effect on injury rates.
The transversus abdominis muscle also plays an important role in force distribution within the kinetic chain through its effects on the sacroiliac joint, where it has been shown to contribute to force closure and shown to stiffen the sacroiliac joint (36,37). Research has indicated that fatigue of the abdominal muscles may contribute to hamstring injuries among football players (10), and decreased neuromuscular trunk control can predict knee injury in collegiate athletes (41). Clinical muscle testing of the transversus abdominis muscle has mainly involved observation of the abdominal wall during a voluntary “drawing-in” maneuver (35). Differences in the ability to perform the drawing-in maneuver have been documented in elite cricketers (17,23) and AFL players (19) with LBP using magnetic resonance imaging (MRI).
There is evidence that specific motor control retraining could have an effect on muscle size and function. A 6-wk motor control training program was delivered to a group of elite athletes (cricketers) with an aim to decrease LBP (18,23). In cricketers with LBP, a decreased CSA of the multifidus (18) and a reduction in the ability to draw-in the abdominal wall was seen (23) when compared with elite cricketers without LBP. Motor control retraining was associated with an increase in CSA of the multifidus muscles and an increased ability to draw-in the abdominal wall. These changes were commensurate with a decrease in pain levels. Although these studies would suggest that motor control retraining of elite athletes is possible and potentially beneficial, a limitation of this study was that the intervention was not randomized and there was no control group.
The aim of this study was to test the effect of a motor control training program on (a) trunk muscle size, asymmetry, and function and (b) availability for selection in competition games for players with or without LBP.
METHODS
Sample
The participants in the study were a cohort of 46 elite players from a club in the national AFL league, representing the entire training squad of the club. All participants gave written informed consent and the rights of subjects were protected. Mean ± SD age, height, and weight of the players was 22.8 ± 3.5 yr, 187.9 ± 6.0 cm, and 88.3 ± 6.6 kg, respectively. The study was approved by the ethics committees of the relevant institutions that hosted the study.
Intervention design
The players were involved in a 22-wk playing season (March to August). A single-blinded, stepped-wedge design intervention trial was staged during this period in three blocks, 7- or 8-wk duration each (Table 1). Group 1 received 15 wk of intervention, whereas group 2 received 8 wk of intervention, thereby enabling assessment of whether a prolonged intervention provided additional benefit to players. It was a requirement of the football club that all players received the intervention during the playing season. Therefore, a panel design was used, in which group 3 acted as a waitlist control group for groups 1 and 2 up until the start of block 3. Group 3 received the intervention during the follow-up period for groups 1 and 2 (last 7 wk of the timetabled competition games). A computer-generated list of numbers provided by a person independent of the study was used to do a complete randomization of the 46 players into one of the three intervention groups. There were no participants lost to follow-up or excluded from the trial. As part of the club’s routine training schedule, a Pilates exercise program was performed weekly from the start of the preseason training period. For the Pilates sessions, the majority of players performed floor programs in groups twice a week for 30 min in duration. Players ceased the Pilates program only while receiving the motor control training program.
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TABLE 1: Intervention design.
Motor control training program
The motor control training program was delivered on site by three physiotherapists with postgraduate qualifications and more than 6 yr of experience using real-time ultrasound imaging for motor control retraining in clinical practice. In addition, each physiotherapist was trained in the specific intervention protocol that was used in this study, so that the program was delivered in a consistent manner between therapists. The motor control program consisted of training the subjects to voluntarily contract the multifidus and transversus abdominis muscles using ultrasound imaging (21) before progressing to functional retraining in upright positions, which focused on spinal position (18,34). Subjects worked on maintaining normal patterns of respiration and developing endurance of the deep abdominal and back muscles. Functional retraining included work in a forward leaning position, sitting to standing, and maintaining a semisquat position for increasing periods of time. These exercises were selected to increase the endurance of the multifidus muscles, which are activated to maintain optimal spinal curves in upright positions (7) and when the center of gravity is displaced anteriorly in the sagittal plane. To further increase resistance, Thera Band exercise bands (The Hygenic Corporation, Akron, OH) were used for both the upper and lower limbs. A Bodyblade (Hymanson, Inc., Marina Del Rey, CA) was also used to train endurance of the trunk muscles. This required subjects to rhythmically perturb a flexible bar and change arms and planes of movement while maintaining their spinal position. This was performed in sitting and semisquat positions and during one- and two-leg squats. Real-time ultrasound imaging was used to provide feedback of muscle contraction during all stages of the motor control program, including functional retraining in upright positions. This allowed players to have precise feedback on the position of the lumbar spine. Feedback of spinal position was also provided to players while they were using a weights bar to simulate work in the weights room. Participants were instructed to maintain good spinal alignment in the weights room and to try to maintain good postural alignment in their daily life, but a written home exercise program was not given. Participants received two sessions of intervention per week each of 30 min in duration under the supervision of qualified physiotherapists. Intervention sessions were given individually for each player, and ultrasound imaging of both transversus abdominis and multifidus muscles was performed. There is level I evidence to support the efficacy of this exercise approach in people with LBP in both restoring multifidus muscle size (18) and decreasing pain, disability, and LBP recurrence rates (12). The main differences between the Pilates program and the motor control training program included player position during exercises (the Pilates program mainly involved players positioned in horizontal positions, whereas the motor control program focused on upright and forward lean positions) and the use of real-time feedback of muscle contraction and spinal position in the motor control program. There was some overlap between the two programs in that players were taught to draw-in the abdominal wall and were taught breathing techniques as part of both programs.
MRI procedure
Assessments of muscle size were conducted in a hospital setting at the start of block 1 (time 1), then after 15 wk of intervention at the end of block 2 (time 2) and finally at the end of block 3 (time 3). Assessments of muscle size and function were conducted using a 1.5-T Siemens Sonata MR system (Siemens AG, Munich, Germany). Operators conducting the imaging were blinded to patient history and group allocation. Participants were first screened by a medical practitioner for contraindications to MRI, which included the presence of metal implants or other metal in the body (e.g., metal fragments in the eye) and claustrophobia. Before the MRI assessment, participants’ height and weight were measured.
The participants were then positioned on the MRI table in a supine lying position with their hips and knees resting on a foam wedge. Standard instructions were provided on how to draw-in the abdominal wall. A True FISP (fast imaging with steady-state precession) sequence using 14 × 7 mm contiguous slices centered on L3–4 disk was used for static images of muscle size. For measurement of abdominal muscle function (19), a cine sequence of one 7-mm slice was taken during a contraction at a frame rate of 500 ms for 7 s. Rest images were performed in a breath hold at midexpiration. Contraction images were commenced after vocal initiation of the contraction by the operator. The cine series was commenced before the initiation of a contraction to ensure complete temporal coverage of the drawing-in maneuver.
Images from MRI were archived for later analysis using a measurement software package on a laptop computer. Image visualization and measurements were conducted using ImageJ version 1.36b (National Institutes of Health, Bethesda, MD; http://rsb.info.nih.gov/ij/). The trunk muscles that were measured included the multifidus, quadratus lumborum, and psoas muscles (Figs. 1A, B, and C, respectively). The multifidus muscle was imaged bilaterally at four vertebral levels, from L2 to L5 (21). The quadratus lumborum and psoas muscles were measured where their CSA is greatest (L3/4 and L4/5 vertebral levels, respectively) (14). A subsequent study has verified that between-side changes in the psoas muscle are consistent across vertebral levels in elite AFL players (38). Measurement of abdominal muscle function included measurement of the CSA of the trunk at rest and on contraction (Figs. 1D, E). For measurements of study data, all MR images were deidentified to ensure the researcher was blinded to group allocation and presenting symptoms.
FIGURE 1: CSA measurements on MRI slices for multifidus muscle (A), quadratus lumborum muscle (B), psoas muscle (C), trunk at rest (D), and trunk contracted (E).
Assessment of LBP
At time 1, all subjects underwent a full musculoskeletal assessment composed of a patient interview and physical examination conducted by a physiotherapist. Based on this assessment, subjects were defined as having no LBP, a history of LBP (not current), or current LBP. LBP was defined as pain localized between T12 and the gluteal fold and severe enough to interfere with sporting or training performance. Players with no LBP had never experienced LBP and did not report pain on examination. Players with current LBP reported pain in the previous week and had one or more positive findings on physical examination. For example, players may have had limited range of motion or reported pain provocation elicited on manual examination of intervertebral joint movement of the lumbar spine. Players who reported past episodes of LBP severe enough to interfere with playing games and training but did not report any current pain or have any positive findings on physical examination were defined as having a history but no current LBP.
The measure of injury used in the study was the availability of players for each weekly competition game. This was based on club records of whether squad members were available for selection or unavailable because of injury, determined by a clinical assessment from the team medical staff. In addition, a process evaluation was conducted by a staff member of the football club. At the end of the respective intervention periods for each group, players were asked questions specifically about the perceived benefit of the motor control training program. All players were asked to rate how much the program helped them (rated on a 10-point scale from “no help” to “extremely helpful”) and an open-ended question asking in what way the program had helped them (multiple responses permitted).
Statistical analysis
Follow-up assessment was conducted with all 46 players in the squad, resulting in a complete data set for analysis. The SPSS Statistics program (version 16; www.spss.com) was used for data analysis, with a level of statistical significance set at P < 0.05. A preliminary ANOVA was used to compare the intervention groups and LBP groups in relation to the measures of age, height, and weight.
The outcome measures for the study were CSA of the multifidus, quadratus lumborum, and psoas muscles; the ability to draw-in the abdominal wall; and the games missed through injury. The effect of the intervention on muscle size, symmetry, and function was conducted separately for each muscle using a type I sums-of-squares model to address the difficulties of higher-order interactions between muscle size, height, and weight (17).
For analysis of multifidus muscle CSA measurements, a MANCOVA was conducted with the vertebral levels of L2, L3, L4, and L5, as the multiple outcome measures. The repeated-measures factors in the analysis were “time” (time 1, time 2, and time 3) and muscle “asymmetry” coded as ipsilateral or contralateral to the preferred kicking leg. Muscle asymmetry refers to the difference of muscle size (CSA) on the kicking leg versus muscle size (CSA) on the support leg. The between-subjects factors were “LBP” (no history of LBP, history of, or current LBP) and intervention “group” (group 1, group 2, and group 3). Age, height, and weight were included as covariates. The use of a MANCOVA accommodates the systematic increase in multifidus size that otherwise results in “vertebral level” being inappropriate as a repeated measure.
For analysis of quadratus lumborum and psoas muscle CSA measurements, a repeated-measures ANCOVA was used. As for the analysis of the multifidus muscle, the factors in the analysis were “time,” “asymmetry,” “LBP,” and intervention “group,” with covariates of age, height, and weight.
For analysis of the players’ ability to “draw-in” the abdominal wall, a repeated-measures ANCOVA was conducted. The repeated-measures factors in the analysis were time and muscle contraction coded as relaxed or contracted. The between-subjects factors were LBP and intervention group, with the factors of age, height, and weight included as covariates.
ANCOVA was also used to test the number of games in the season that players missed due to injury, comparing those who received the intervention early (groups 1 and 2) versus late (group 3) in the season. The repeated-measures factor was time and the between-subjects factors were LBP and intervention group, with age, height, and weight included as covariates.
RESULTS
The mean ± SD age, height, and weight of all the players was 22.8 ± 3.5 yr, 187.9 ± 6.0 cm, and 88.3 ± 6.6 kg, respectively. The age, height, and weight of players in each intervention group were as follows: 22.7 ± 3.6 yr, 188.0 ± 5.4 cm, and 87.6 ± 7.5 kg for group 1; 22.5 ± 3.2 yr, 188.2 ± 5.5 cm, and 89.1 ± 6.8 kg for group 2; 23.1 ± 3.9 yr, 187.4 ± 7.5 cm, and 88.2 ± 5.6 kg for group 3. Of the 46 players, 13 reported current LBP (4 in group 1, 5 in group 2, and 4 in group 3), 14 had a history of LBP (6 in group 1, 2 in group 2, and 6 in group 3), and 19 did not have LBP (7 in group 1, 8 in group 2, and 4 in group 3). There was no statistically significant association between the number of players with or without LBP or a history of LBP, and the distribution across the three intervention groups (χ2 = 3.6, P = 0.46).
Muscle Assessments
Multifidus muscle
Results of the multivariate analysis of multifidus muscle CSA showed a statistically significant effect across time (F = 7.7, P < 0.0001), but there were no effects found for muscle asymmetry or LBP (P > 0.05). There was a significant interaction effect between intervention group and time (F = 2.8, P < 0.0001) in which each vertebral level (L2–L5) contributed positively to the result. Post hoc tests of the means shown in Table 2 indicated that, during the playing season, the 15-wk (group 1) and 8-wk (group 2) intervention program increased multifidus muscle size by time 2 relative to group 3 (waitlist control) for all vertebral levels. Group 3 showed little change in multifidus size for L2 and L3 and a decrease in multifidus muscle size for L4 (9.4%) and L5 (9.3%) during this same period. When group 3 received the intervention in block 3 (follow-up period for groups 1 and 2), multifidus muscle size increased by time 3 (except for L2). The means in Table 2 indicate that the intervention group 1 (15 wk) did not show greater hypertrophy of multifidus compared to group 2 (8 wk). On average, across L2–L5, there was a 10.4% increase in multifidus CSA. The percentage changes across times 1–3 indicate hypertrophy of the multifidus muscle between 6% and 26% due to the intervention. The effect sizes of the intervention were calculated on the difference in means divided by the pooled SD (based on the difference scores between time 1 and time 2 averaged across side). The effect sizes (groups 1 and 2 vs group 3) were 1.70 at L5, 1.17 at L4, 0.80 at L3, and 1.04 at L2.
TABLE 2: CSA of the multifidus muscle (cm2) at each vertebral level for the three intervention groups during the playing season.a
Other muscle measurements
With regard to the main hypothesis, results for the measures of quadratus lumborum and psoas muscle CSA showed no statistically significant effects for interaction between intervention group and time (P > 0.05). However, the mean CSA of the quadratus lumborum muscle showed a 6.6% increase from time 1 (9.0 ± 0.22) to time 3 (9.6 ± 0.25; F = 17.4, P < 0.0001) and an effect for asymmetry (F = 6.9, P = 0.013), which indicated that this muscle was 4.3% larger on the side contralateral to the kicking leg throughout the season (9.4 and 9.0 cm2, respectively). Mean psoas CSA (mean ± SE) showed an increase from time 1 (24.2 ± 0.4) to time 3 (25.0 ± 0.4; F = 8.9, P < 0.001) and a significant interaction between asymmetry and time (F = 39.2, P < 0.0001) in which the initial asymmetry at the start of the playing season (23.5 ± 0.4 and 25.0 ± 0.4; 6.2% larger on the preferred kicking leg) decreased by the end of the season (24.9 ± 0.4 and 25.1 ± 0.4; 0.9% larger).
The ability to perform the abdominal drawing-in maneuver (relative difference between trunk CSA at rest vs contraction) showed a main effect for muscle condition (F = 244.1, P < 0.001), indicating a 5.6% overall decrease in trunk CSA (mean difference = 22.5 cm2) associated with drawing-in (relaxed vs contracted condition) and a main effect for time (F = 5.7, P = 0.005), in which the average of trunk CSA (at rest and on contraction) was 3.8% more at time 3 than time 2. A trend was noted for the interaction of muscle condition and time (F = 2.8, P = 0.07). Closer examination of the means (Table 3) indicated that the percentage difference between the relaxed and contracted conditions increased from time 1 to time 2 by 24.4% for group 1 and 46.5% for group 2, whereas the percentage difference for group 3 showed a decrease from time 1 to time 2. This was further examined by a post hoc analysis of groups 1 and 2 combined versus group 3, which indicated a statistically significant group difference in trunk CSA associated with drawing-in the abdominal wall (F = 4.9, P = 0.03).
TABLE 3: CSA of the trunk (rest vs contracted and difference, cm2) for each intervention group during the playing season.a
Player Unavailability for Games Due to Injury
Thirty-four (72%) of the players incurred an injury during the playing season, which resulted in their unavailability for one or more competition games. Almost all the injuries were located below the hip (hip, groin, thigh, or lower limb) and only four of the injuries were located above the hip (back, shoulder, or hand). Because two of these players also had injuries below the hip, all injuries were included in the assessment of availability. Games missed due to other illness were not included in this measure. Player availability across the season ranged from 4 to 22 games with a mean ± SD of 18.2 ± 4.4.
Analysis of player unavailability indicated that, during the whole playing season, players in groups 1 and 2 who received the intervention by time 2 missed fewer games than players in group 3, who had not received the intervention at this time (F = 3.4, P = 0.04). Post hoc contrasts indicated there was no “group” differences from time 1 to time 2 (F = 1.4, P > 0.05), but a significant “group” difference from time 2 to time 3 (F = 4.8, P = 0.035). The means in Table 4 indicate that of the 22 games played in the season, the groups who received the intervention early in the season missed an average of 3 games owing to injury and those in group 3 missed an average of 5.6 games. There was no significant effect due to LPB (P > 0.05) and no significant interaction between LBP and intervention “group” (P > 0.05).
TABLE 4: Number of games missed due to injury.a
Perceived Benefit of the Program
At the end of the respective intervention periods, players were also asked questions specifically about the motor control training program. Analysis of data for the process evaluation was conducted for two indicators of perceived benefit from doing the program. Ratings of the perceived helpfulness of the program indicated that 87% of the players felt it had helped. Perceived benefits from doing the program are shown in Table 5.
TABLE 5: Perceived benefit of the motor control training program.a
DISCUSSION
Multifidus muscle
The results from this study showed that the multifidus muscles of players who did not receive the motor control training program by time 2 decreased in size at the L4 (9.4%) and L5 (9.3%) vertebral levels during the playing season. Atrophy of the multifidus muscles at the L4 and L5 vertebral levels was demonstrated previously in a longitudinal study of AFL players (16). Although the methodology of the current study precludes examination of the mechanism of multifidus muscle atrophy, a possible explanation is the development of muscle imbalance related to training and playing AFL in which hypertrophy of one muscle group may correspond with atrophy of an opposing group. AFL is a flexor dominant sport, and players have previously been shown to have large psoas muscles at the L4 and L5 vertebral levels (38). Atrophy of the multifidus muscles may therefore be related to the large opposing psoas muscles at these levels. The lower lumbar vertebral levels may have been affected the most as these levels link the lower kinetic chain and the vertebral column. Anatomically, the size of the lumbar multifidus is largest at the lumbosacral junction (1) where biomechanical forces are high (4). The results of this study also showed that, by time 2, the decrease in multifidus size seen in the control group was not evident for the groups who had received the motor control training program. The intervention did more than counter the atrophy of the multifidus muscle; it was related to an increase in the size of this muscle during this same period. Across vertebral levels L2–L5 on average, there was an increase in multifidus muscle size by 10.4% for the intervention groups 1 and 2 by the time 2 assessment point. The increased length of intervention for group 1 (15 wk) versus group 2 (8 wk) preceding measurements at time 2 did not seem to provide an additional benefit. However, as seen in Table 2, players in groups 1 and 2 showed a decrease in the size of the multifidus muscles at time 3 (after 7 wk of no intervention). This result suggests that a maintenance program may be required throughout the season.
Assessment of LBP
LBP has previously been associated with a decrease in CSA of the multifidus muscle in elite cricketers (18). Specific motor control training using an intervention similar to that adopted in the current investigation was also successful in restoring multifidus muscle size and commensurate with decreased LBP. Atrophy of the multifidus muscles is considered an adverse event for people with LBP (15). The mechanism of atrophy of the multifidus muscles associated with LBP has been examined by producing experimental disc injuries in animal studies (24). The CSA of the multifidus muscles was measured before and after lesions were produced. Multifidus CSA was reduced at the vertebral level ipsilateral to the disc lesion. These findings would suggest that the sequela to damage of a lumbar structure such as the disk is segmental atrophy of the multifidus muscle. However, in the current investigation, there was no relationship between LBP and muscle size of the multifidus. This result suggests that the changes in morphology of these muscles were related more to training and playing football. The main difference between the findings from the studies of cricketers (18,23), and the current study of AFL players is that the cricket studies relate to restoring motor control after LBP, with an aim of reducing LBP. The current study has demonstrated another potential benefit of this approach, related to reducing the occurrence of lower limb injuries in football players.
Quadratus lumborum and psoas muscles
For the quadratus lumborum and psoas muscles, there was no demonstrated difference in muscle size or symmetry associated with intervention. This is most likely related to the intent of the intervention program, which targeted the abdominal and back muscles. An interesting finding was that the size of the quadratus lumborum and psoas muscles was seen to increase in players over the football playing season. The psoas muscle is a powerful hip flexor that has the capacity to exert substantial loads on the lumbar spine owing to its attachment to the vertebral column (6). As the size of the multifidus muscles concurrently decreased in the control group, this finding could represent a muscle imbalance that developed during the playing season, as suggested by previous research (16). The size of the psoas muscles in the AFL players in this study was shown to be large, and results are consistent with previous studies that have used similar measurement protocols (14,38). Functionally, the psoas muscle is active when hip flexor torque is required (2), for example, during the backswing and wind-up phases of the kicking motion. The large size of the psoas muscle in AFL players is most likely related to its role as a primary hip flexor (6,32), as has been documented in gymnasts, ballet dancers, figure skaters (31), and cricketers (33). Psoas muscle CSA from the current study are considerably larger and less variable than those reported for male nonathletes (18.9 ± 3.8 cm2) (29) and active (non-AFL playing) males (22.1 ± 3.6 cm2) (31,33). The pattern of asymmetry seen in the current study was similar to that reported in other AFL studies (14,38), with larger quadratus lumborum muscles on the stance leg (9.4 and 9.0 cm2) and larger psoas muscles on the kicking leg (24.8 and 24.2 cm2).
Abdominal drawing-in maneuver
Of the abdominal muscles, the transversus abdominis has been considered an important muscle to target in motor control training programs. The reason for this is that the muscle has direct attachments to the lumbar vertebrae via the thoracolumbar fascia, and proposed mechanisms for this muscle contributing to lumbopelvic stability include generation of intra-abdominal pressure (25), tension in the thoracolumbar fascia (3,25), and force closure of the sacroiliac joints (36,37). The current study showed that when results from group 1 (who received 15 wk of intervention) and group 2 (who received 8 wk of intervention) were combined, the ability to draw-in the abdominal wall after the intervention was improved significantly (mean increase = 35.5%) when compared with the results from group 3 who had not received the intervention (decreased by 3.8%). The mean draw-in of the abdominal wall (relaxed − contracted trunk CSA; mean ± SE) at time 2 was 27.0 ± 3.1, 27.4 ± 3.3, and 20.0 ± 3.7 cm2 for groups 1, 2, and 3, respectively. Two other studies have measured the abdominal drawing-in maneuver using similar methodology (19,23). AFL players (without LBP) were shown to be able to decrease the CSA of the trunk by 29.9 ± 5.2 cm2 (19) and elite cricketers by a mean of 31.4 ± 3.1 cm2 (23). In both these studies, athletes with LBP were shown to have a decreased ability to draw-in the abdominal wall (19,23), and this improved with motor control retraining (23). In the present study, this change for those with LBP was not found. This is most likely a result of all players routinely performing Pilates, as drawing-in the abdominal wall was a component of these exercises. However, the results of the current study showed that specific motor control training still produced a significant improvement in this ability, indicated by the difference between results for groups 1 and 2 versus group 3 who had not received the intervention. Notably, the 15-wk intervention group did not show a greater improvement in abdominal function compared to the 8-wk intervention group (Table 3).
Games missed
The results of the current study showed that, during the whole playing season, players in groups 1 and 2 who received the intervention by time 2 were available for more games than those in group 3 (who received the intervention late in the season). Of the 22 games played in the season, the groups who received the intervention early in the season missed 13.6% of the games on average compared with 27.3% of the games for players in group 3. Possible explanations for this finding may relate to the intervention targeting deficits in neuromuscular control of the lumbopelvic region. For example, these deficits have previously been proposed to affect the dynamic stability of the knee because this deficit may contribute to instability throughout the segment of the kinetic chain (13,41). Furthermore, Cowan et al. (8), showed an association between a delay in activation of the transversus abdominis muscle and long-standing groin pain. Because stability of the lumbopelvic region involves dynamic trunk control to allow production, transfer, and control of forces and motion to the distal segments of the kinetic chain (27), good control of the lumbopelvic area is likely to be required to meet the high demands imposed on the body in a sport such as AFL. Improved motor control of the lumbopelvic region in players who received the intervention in the current investigation is a plausible explanation for the increased availability of players in groups 1 and 2. The lack of any significant effects for LBP on games missed due to injury indicates that the relationship between intervention group and injury was not mediated or moderated by LBP.
FUTURE DIRECTIONS AND LIMITATIONS
A limitation of this study may be the relatively small sample size, although it is similar to other studies of athletes. In addition, a priori power calculation of the required sample size was not conducted as the number of players in the squad is capped by the club. However, the high effect sizes for the intervention indicate that the small sample size did not unduly increase the type 2 error rate for the study. The results of this study apply to elite football players but may be generalized to other football codes. A similar intervention has shown benefits for elite cricketers with LBP, suggesting that the results may apply to other sporting activities. However, further studies are needed to confirm that the effect of motor control training consistently affects muscle size and sporting-related injuries and generalizes to other sports. Because no additional benefit was attributed to a longer intervention period, future studies could examine the benefit of a shorter intervention period. In addition, the use of a more direct measure of injuries other than games missed and a more detailed examination of the role of LBP need to be investigated. The effect of implementing the program in the preseason also needs to be examined.
In conclusion, although there are many factors to consider in association with decreasing rates of injuries in elite footballers, motor control training represents one approach, which may be beneficial. Ideally, this program could be conducted each year, to provide an update for players and initiate new recruits to the club.
This study was funded by a sports medicine research grant provided by the Brisbane Lions Australian Football Club.
The authors thank the football players who participated in the study, Nathan Carloss (physiotherapist, Lions AFC), Lachlan Penfold (performance manager, Lions AFC), Assoc. Prof. Steve Wilson (School of ITEE, The University of Queensland), Dr. Mark Strudwick (University of Queensland Centre for Advanced Imaging), and the physiotherapists who assisted on the project.
The authors have no conflicts of interest.
The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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