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(1) CHANGES IN ISOKINETIC HAMSTRINGS AND QUADRICEPS STRENGTH IN ACADEMY SOCCER PLAYERS DURING A 40-WEEK MACROCYCLE


Authors:

Mark Stone, PhD MSc ASCC – Senior Lecturer in Strength and Conditioning, University of Central Lancashire

Karl Gibbon – Senior Research Officer, Liverpool John Moores University

Abstract:

Isokinetic peak torque (PT) and functional hamstrings to quadriceps ratio (H:Q) provide useful information about knee-joint strength and stability. Lenhart et al. (1) has previously shown that H:Q measured at an angular velocity of 60o·s-1 remains unchanged throughout a soccer season. However, changes in the torque-producing characteristics of these muscles are velocity specific and injuries tend to occur during joint movements at higher velocities. Changes in H:Q throughout the season could have important implications for training prescription and load management, therefore further research is needed to evaluate within-season changes in H:Q, at higher angular velocities. PURPOSE: The purpose of this study was to investigate whether any systematic changes in H:Q measured at a high angular velocity occur during a 40-week macrocycle. METHODS: Fourteen full-time male academy players (Mean ± SD; Age: 18.7+0.3 years; Height: 179.4+5.7 cm; Mass: 74.1+7.9 kg) from a professional soccer club in the UK volunteered to take part in this study. Players attended the laboratory during weeks one and six (the start and end of preseason) and weeks 23 and 40 (the middle and end of the competition phase) of the macrocycle.  During each visit, participants performed a RAMP warm up and a familiarisation on the dynamometer before completing the isokinetic test battery described in Crosier et al. (2). H:Q was calculated as the ratio between PT during eccentric-hamstrings and concentric-quadriceps exercise at angular velocities of 30 and 240o·s-1, respectively. An angular velocity of 30o·s-1 was deemed appropriate for the eccentric task because isokinetic measurements of eccentric-torque undertaken at high velocities are subject to high levels of measurement error, and in isokinetic testing the eccentric torque-velocity curve is relatively constant (2). Temporal changes in PT and H:Q were evaluated with a repeated-measures ANOVA. Significant main effects were followed up with Bonferroni-adjusted confidence intervals. RESULTS: At week six, H:Q was between 0.01-0.43 lower in the dominant leg (F13,3=3.61, p=0.02) and between 0.08-0.44 lower in the non-dominant leg than in week one (F13,3=5.52, p< 0.01). In the non-dominant leg this decrease in H:Q was attributable to a 2.4–49.4 N·m decrease in eccentric PT of the hamstrings (F13,3=3.77, p=0.02). H:Q in weeks 23 and 40 were not significantly different to any other time point, however concentric PT of the quadriceps in the non-dominant leg was between 0.2–37.7 and 5.1–44.1 N·m greater at weeks 23 and 40 than week one (F13,3=6.22, p< 0.001).  CONCLUSIONS: Several soccer teams routinely assess isokinetic strength of the hamstring and quadriceps at the start of preseason. However, the results of this experiment indicate that even players who present with normal H:Q may experience a decrease in eccentric hamstring PT which can have a deleterious effect on H:Q during the pre-competition phase. Conversely, concentric PT of the quadriceps at a high angular velocity increased during the competition phase.  PRACTICAL APPLICATIONS: Strength and conditioning coaches should be conscious of within-macrocycle changes in the torque-producing characteristics of the hamstring and quadriceps, and manage training-load accordingly.  Further research is warranted to investigate the effects of targeted interventions to maintain eccentric-hamstring PT during preseason in academy soccer players.

References
Croisier, JLS, Ganteaume, J, Binet, M, Genty, Ferret, J-M. Strength imbalances and prevention of hamstring injury in professional soccer players: A prospective study. Am J Sports Med 36: 1469-1475, 2008.
Lehnert, M, Xaverová, Z, De Ste Croix, M. Changes in muscle strength in U19 soccer players during an annual training cycle. J Hum Kinet 42: 175-185, 2014.

 

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