While estimating which muscle groups play a role in kicking has been reported through calculating net muscle torques about the joints, the specific temporal activity of muscle groups has been researched through studying electromyography (EMG) recording (Dörge et al., 1999).
2.2.2.5.1 Timing of Muscle Activation in Australian Football
There has not been an abundance of studies that have focussed on the kinetics or EMG of the Australian Football kicking technique. In the only published study that recorded EMG during an Australian Football kick, Orchard et al. (1999) looked at the bilateral
quadriceps, hamstrings and gluteals of both legs, along with the rectus abdominus of four professional Australian Football players, and qualitatively compared the muscle activation to lower body kinematics. Players were instructed to run in (six to eight steps) and kick the ball at an imaginary target 40m in front of them. The authors expressed muscle activity as a percentage of the maximum value recorded (not reported) at any of the six stages of the kick. The quadriceps of the kicking leg acted eccentrically in the wind-up phase (≈ 52 ± 9%), then concentrically in the forward swing (≈ 31 ± 9%), and were the most active group studied. The hamstrings of the kicking leg acted concentrically to initiate the backswing (≈ 40 ± 8%) and showed variable eccentric activity during the follow through (≈ 20 ± 18%), where two subjects showed minimal activity and the other two showed significant eccentric activity. This eccentric activity may also be a safety mechanism to protect the joints from injury, as was proposed by Dörge et al. (2002) when analysing negative muscle moments towards the end of the kick. It was concluded that the high activity in quadriceps of the kicking leg, gluteals of the stance leg, both
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hamstrings and rectus abdominus assist in explaining the high rates of muscular injury in Australian Football (Orchard et al., 1999).
2.2.2.5.1.1 Link of Timing of Muscle Activation to Injury
Muscle activation has been speculated to be linked to injury during kicking. Hamstring strains, knee injuries and groin injuries are the most common injuries in Australian Football, with hamstring, quadriceps and groin injuries occurring more commonly than in Australia’s other football codes (Orchard, Wood, Seward & Broad, 1998; Orchard et al., 1999). Repetitive loads in kicking and relatively long game durations have been proposed as two of the possible factors that may explain the comparatively higher incidences of hamstring and groin injuries. Kicking has been proposed to almost certainly increase the rate of quadriceps strain. Any study that looks at the major lower limb muscles during kicking should be able to give an insight into the injury patterns in Australian Football and could lead to injury prevention (Orchard et al., 1999).
2.2.2.5.2 Timing of Muscle Activation in Soccer
There has also been a limited amount of EMG research done on soccer kicking. Dörge et al. (1999) studied EMG activity of five kicking leg muscles (m. gluteus maximus, m. vastus lateralis, m. rectus femoris, m. biceps femoris and iliopsoas) and how it compared to the kinetics of the kicking leg during a soccer place kick. The results showed there to be a clear proximal to distal segmental motion, a sequence also followed with the EMG patterns, expressed as % of maximal EMG amplitude from maximal voluntary
contractions, recorded from the muscles (normalising EMG values a percentage of maximum isometric activity (MVC) has been used in non-kicking soccer research)
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(Gissis, Nikolaidis, Sotiropoulos & Papadopoulos, 2004). This sequence started with activation of the m. iliopsoas (which was active during the entire motion), followed by the rectus femoris, then the vastus lateralis. The activity of these muscles was often close to 100%. Leading up to impact, in the period when the angular velocity of the thigh was positive, the activity of the m. Iliopsoas averaged 79.4% (peak 98.3% (80.0-121.1%)), m. rectus femoris averaged 46.3% (peak 93.7% (79.1-99.9%)). There was smaller activity in the m. biceps femoris at 22.6% (peak 40.1% just before impact) and m. gluteus maximus at 10.2% (peak 27.1% just before impact) during the same period. In a period of knee extension the activity of the m. vastus lateralis was 81.7% (peak 101.6% (91.6-112.3%)) (Dörge et al., 1999). The net muscle torques about the hip and knee were positive during almost the entire time. EMG peaks for the iliopsoas and rectus femoris muscles coincided with the peak net muscle torque about the hip joint. Following the peak net muscle torque about the hip joint, there was an observed smaller peak net muscle torque around the knee joint. This peak coincided with the EMG peak from the rectus femoris and with an increase in activity from the vastus lateralis. A decrease, followed by another increase in net muscle torques at the hip and knee joint respectively was then observed, almost repeating the prior peak muscle torque pattern. The second torque pattern was thought to be due to a decrease in the activity of the biceps femoris. A rapid decrease in net muscle torque just before impact followed and was thought to be due to an increased activation of the biceps femoris and gluteus maximus. However, there was only a slight torque reversal around the hip just before impact, with angular deceleration of the thigh failing to increase the angular velocity of the shank (work -3.57 to 0.0%). Therefore no positive work on the shank was observed from a deceleration of the thigh. The positive work on the shank originated from the net extensor torque about the knee joint and the torque produced by the centripetal force (circular movement) of the thigh. The hip flexor muscles, including
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the m. iliopsoas, were activated even during the deceleration of the thigh, and as concluded it thus indicates the importance of maintaining angular velocity of the thigh during the motion, and therefore performing work on the shank (Dörge et al., 1999).
Another study by Manolopoulos et al. (2006) looked specifically at EMG activity of the rectus femoris (RF), vastus medialis (VM) and the long head of the biceps femoris (BF) of the kicking leg, and the rectus femoris, biceps femoris and medial head of the gastrocnemius of the support leg of amateur players performing a soccer instep kick. Similar to Orchard et al. (1999), but in contrast to Dörge et al. (1999), the EMG measurements were normalised by dividing the data by the maximum EMG of each muscle during each kick. Participants were divided into two groups, with one group to act as the control group (n = 10) and the other an experimental group which was given a training program (n = 10). The pre training results from the kicking leg of the
experimental group are presented next. EMG activity was recorded during three phases. These results were recorded from the start of the movement to the contact of the support leg on the ground (RF 47.8 ± 17.4%, BF 38.9 ± 23.9%, VM 33.1 ± 13.7%), from ground contact of the support leg until the smallest knee angle of the kicking leg (RF 85.5 ± 20.5%, BF 40.1 ± 20.3%, VM 66.9 ± 16.5%), and from the smallest angle of the kicking leg until ball contact (RF 59.1 ± 27.5%, BF 54.1 ± 27.2%, VM 54.4 ± 14.0%). These RF values were slightly more (12.8% more), whilst the BF was much higher (31.5% more) than the pre-impact Australian Football kicking values reported by Dörge et al. (1999). Results reported by Manolopoulos et al. (2006) indicated that the activation patterns of the muscles examined were not significantly affected by the training program. The exception was the vastus medialis which displayed significantly higher activity in the latter stage of the kick for the experimental group (before 54.4 ± 14.0%, after 70.8 ± 15.6%). This indicates that higher force may be produced during this phase for the experimental group.
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However, as the authors point out, the contribution of the vastus medialis to knee
extension muscle torque is unclear as it is only a component of the knee extensor muscle group. Another possible limitation of the study was the EMG normalisation technique used. Training effects on EMG data may affect the magnitude of the reference value and the value during the kick, therefore possibly masking the true effects of the training program (Manolopoulos et al., 2006). Other limitations in the reporting of EMG values is that inaccurate positioning of electrodes can lead to cross contamination of results and the number of muscles investigated is limited by the equipment and the number of channels available (Baczkowski, Marks, Silberstein & Schneider-Kolsky, 2006).
Due to differences in the recording of kick durations, it is difficult to compare Australian Football and soccer EMG data. However, it is clear that both the quadriceps and hamstrings are active during kicking, with the quadriceps being more dominant.