How A Footballers Reliance On 'One Foot' Can Hinder Recovery
The Effect of Footedness on Match-Play Fatigue and Post-Match Recovery
Football is an intermittent sport involving sprints, rapid changes of direction, and jumps, with research revealing that a football player might make as many as 1300 of these high intensity actions in just one match. Add to this the tendency for players to be either right-footed or left-footed and there’s potential for one leg to work harder than the other during competitive games. The question is, will this lack of symmetry affect performance as the muscles begin to fatigue, and will it lead into differences in recovery times post-match?
Footedness in Football
Statistics show that roughly 80 per cent of people across the world are right-handed, and the remaining 20 per cent are left-handed, with only about 1 in every 100 people classed as truly ambidextrous. Footedness generally follows suit, with only a few right-handed people being left-footed, and vice versa.
Not many sport-specific studies have been done, but the limited research available concludes that footballers are no different to the general population with 80 per cent playing right-footed, 20 per cent playing left-footed, and only 1 per cent of players being truly two-footed.
The findings of a study analysing the footedness of players in the 1998 World Cup suggest that while some players are able to demonstrate equal levels of skill using both left and right feet, they still favour one over the other when they’re in contact with the ball, whether in set pieces, passing, dribbling, tackling, or first touches.
The conclusion drawn from this was that football skills can be learned and practised using both feet, but biological preferences (right-footed or left-footed) still dominate in match-play.
Footedness and Fatigue
Elite footballers generally play in excess of 70 matches per season and take part in anything from 3 to 6 training sessions each week.
Studies have shown that the repeated need for the non-kicking leg to stabilise a player, and to absorb the ground reaction forces as the ball is kicked, can negatively impact sports performance markers such as sprint speed, change of direction agility, and jump height, and increase the risk of injury in the hip, knee, and ankle.
A study involving elite adolescent male footballers was set up to determine the effects of competitive match-play on one-sidedness, specifically the effects of one leg working harder than the other.
The participants were asked to perform a one-legged vertical jump from a force plate. Hands had to be kept on hips and the non-jumping leg held up off the floor with hip and knee flexed so that no other movements could influence the jump height.
The aim was to jump as high and as fast as possible so that a maximal effort vertical jump height could be recorded. This was repeated to give individual measures for both the right leg and the left leg.
The measures included:
- Eccentric impulse (the lowering phase in preparation for jumping)
- Concentric impulse (the phase from applying the brakes to stop the lowering up to the point of take-off)
- Peak force (the maximum force produced on take-off)
- Jump height (this was calculated using the velocity at take-off)
- Landing impulse (the ground contact force up until peak landing force)
- Peak landing force (maximum force obtained during the landing)
Key Study Findings
- Interlimb asymmetries, meaning the differences between right leg and left leg, were noted as small in the pre-match jump height measurements.
- Interlimb asymmetries increased significantly post-match, up to 3.7 times greater than pre-match.
- Signiﬁcant negative changes were noted in all jump performance measurements at all time points, with jump height being the only exception.
- Jump height measurements, especially in the left leg, decreased post-match, but a return to pre-match measures was noted at the 24-hour time point (earlier than the 48-hour time point noted in other jump measurements).
- At each of the time points from post-match onwards, a significant decrease was recorded in eccentric impulse, peak force on take-off, and landing impulse which generated a significant increase in peak landing force.
- Asymmetries in landing impulse and peak landing force reached their greatest at the 24-hour post-match time point, only showing a return to pre-match measures at the 48-hour time point.
- Further signiﬁcant decreases in eccentric impulse and peak force on take-off were noted at the 48-hour and 72-hour time points in the left leg.
What Do These Findings Mean in Real Terms?
The frequent sprints, rapid accelerations and decelerations, and multi-directional turns involved in a game of football all take their toll on players, leading to muscle fatigue in the later stages of a match.
Understanding the effect of fatigue on football performance is important, not only during a match, but also in terms of post-match recovery.
The results of the study show that interlimb asymmetries become far greater after competitive match-play, and that jump height alone is not a good measure of these changes. The return of jump height to pre-match measurements at the 24-hour post-match time point would suggest that a full recovery has been made, but in all other measurements, recovery from the effects of fatigue only become evident after the 48-hour post-match time point.
The differences in performance between right leg and left leg were also noted to be at their greatest between 24 and 48 hours after match-play. With most players taking part in training the day after a competitive match, this raises the question of whether standard training practises and recovery times are sufficient in terms of keeping players performing at their best, and if the increased measure of difference between right leg and left leg performance could be placing players at greater risk of injury during this period.
Increased Injury Risk
The heavier landings, demonstrated by the significant increase in peak landing force recorded in post-match measurements, could be putting players at an increased risk of injury, with previous studies linking heavy landings to potential hip, knee, and ankle injuries.
Other studies have shown that fatigue in the later stages of a competitive match has a negative impact on the functional hamstrings-to-quadriceps ratio, placing players at a greater risk of picking up injuries such as hamstring tears and ACL (anterior cruciate ligament) sprains.
Applying the Research in Football
The lack of symmetry created by favouring one leg over the other in competitive football matches will affect performance as the muscles begin to fatigue, and it will lead into differences in recovery times post-match.
Research results are inconclusive with some studies suggesting that a difference of 15 per cent between right leg and left leg performance is the threshold where the risk of injury increases, but others suggesting a threshold of just 10 per cent.
In a separate study involving youth female footballers, jump height asymmetries of as much as 12 per cent were recorded in some players. These differences were shown to have a negative impact on sprint times and jump performance compared to players with lower percentages of difference.
The conclusion of the study was that players with smaller asymmetries out-performed those with larger differences between right leg and left leg performance.
However, the research surrounding the study of elite players in the 1998 World Cup has shown that footedness is a biological preference, and even though many players can perform training drills with equal skill using either leg, one leg still dominates when it comes to competitive match-play.
With this being the case, the researchers leading the study on the effects of footedness on match-play fatigue and post-match recovery believe that unilateral CMJ tests (one-legged countermovement jump tests) would provide a clearer measure of the effects of fatigue in players compared to the more commonly used bilateral CMJ tests in which players jump using both legs.
Monitoring differences between the right leg and left leg could help strength and conditioning coaches to determine whether existing imbalances are negatively impacting performance in unilateral moves such as sprinting, changing direction, and kicking, and provide a more accurate measure of post-match increases in asymmetry that could increase a player’s risk of injury.
The Bottom Line
Interlimb asymmetries exist in footballers, even in elite players, leading to one leg working harder than the other in competitive matches.
Research suggests that monitoring the percentage of difference in performance from one leg to the other could hold the key to making improvements in training, and, perhaps most importantly, adapting post-match training loads on an individual basis.
When asymmetries are at their greatest, the increased risk of injury is at its greatest, so unilateral jump tests at scheduled post-match intervals would make it possible to gauge when a player has recovered from the effects of fatigue and when the side-to-side differences have returned to pre-match measures.
Less injury time means more training and playing time, which means greater potential for improvement.
Bromley, T, Turner, A, Read, P, Lake, J, Maloney, S, Chavda, S, and Bishop, C. Effects of a competitive soccer match on jump performance and interlimb asymmetries in elite academy soccer players. J Strength Cond Res XX(X): 000–000, 2018
Carey et al., “Footedness in world soccer: an analysis of France ’98” (2001) J Sports Sci. 2001 Nov;19(11):855-64.