Matt Greig

The effects of multidirectional soccer-specific fatigue on markers of hamstring injury risk

The purpose of this work was to investigate the effect of multidirectional soccer-specific fatigue on hamstring muscle strength and angle of peak torque. Sixteen male semi-professional soccer players (mean+/-S.D.: age: 21.3+/-2.9 years; height 185.0+/-8.7 cm; body mass 81.6+/-6.7 kg) completed the SAFT(90), a multidirectional, intermittent 90-min exercise protocol based on data from English Championship soccer matches. Prior to exercise (t(0)), at half-time (t(45)) and post-exercise (t(105)), subjects performed three maximal dominant limb isokinetic contractions (Biodex, System 3) at 120 degrees s(-1) through a 90 degrees range for concentric and eccentric knee flexors and concentric knee extensors. Analysis of variance revealed significant time dependant reductions in gravity corrected eccentric hamstring peak torque, and consequently in the functional hamstring:quadriceps ratio (P<0.01). Eccentric hamstring peak torque decreased significantly during each half (t(0): 272.0+/-43.2; t(45): 240.4+/-43.3; t(105): 226.3+/-45.7 Nm). The functional hamstring:quadriceps ratio also decreased significantly during each half (t(0): 116.6+/-21.2; t(45): 107.1+/-17.6; t(105): 98.8+/-20.3%). There were no significant changes in concentric hamstring or quadriceps peak torque observed during SAFT(90) (P>0.05). Data analysis also revealed significant differences for Angle of Peak Torque for eccentric hamstrings (P<0.05) which was significantly higher at the end of each half (t(45): 37+/-15; t(105): 38+/-18 degrees ) than the pre-exercise value (t(0): 28+/-12 degrees ). There was a time dependant decrease in peak eccentric hamstring torque and in the functional strength ratio which may have implications for the increased predisposition to hamstring strain injury during the latter stages of match-play.

Attentional Focusing Instructions Influence Force Production and Muscular Activity During Isokinetic Elbow Flexions

Marchant DC, Greig M, and Scott C. Attentional focusing instructions influence force production and muscular activity during isokinetic elbow flexions. J Strength Cond Res 23(8): 2358-2366, 2009-Appropriate verbal instruction is critical to effective guidance of movements. Internal (movement focus) and external (outcome focus) attentional focusing instructions have been shown to influence movement kinetics and muscular activity; this study investigated their effects during a force production task. Twenty-five participants (mean age of 22.72 ± 1.88 years) completed 10 repetitions of single-arm elbow flexions on an isokinetic dynamometer while electromyographical activity of the biceps brachii and net joint elbow flexor torque were measured. Three trials were completed: a control trial to attain maximum voluntary contraction (MVC) data, followed by counterbalanced trials internal and external attentional focus conditions. The external focus exhibited a significantly (p < 0.05) higher peak net joint torque (102.10 ± 2.42%MVC) than the internal condition (95.33 ± 2.08%MVC) and also a greater integral of the torque-time curve (99.90 ± 2.91%MVC) than the internal condition (93.80 ± 2.71%MVC). In addition, the external focus resulted in lower peak electromyography (134.43 ± 16.83%MVC) response when compared with the internal focus condition (155.23 ± 22.54%MVC) as well as lower mean integrated electromyography (127.55 ± 12.24%MVC) than the internal condition (154.99 ± 19.44%MVC). Results indicate that an external attentional focus results in significantly greater force production and lower muscular activity during isokinetic elbow flexions when compared with an internal focus. When instructing clients during maximal force production tasks, practitioners should tailor their instructions to emphasize an external focus of attention. Specifically, attention should be directed onto the movement of the object being moved and away from the specific bodily movements involved in the action.

The Influence of Soccer-Specific Fatigue on Peak Isokinetic Torque Production of the Knee Flexors and Extensors:

Background Epidemiological findings of higher muscular thigh strain injury incidence during the latter stages of soccer match play have been attributed to fatigue. Hypothesis Soccer-specific fatigue will significantly reduce peak isokinetic torque of the knee flexors and extensors. Study Design Descriptive laboratory study. Methods Ten male professional soccer players (mean age, 24.7 ± 4.4 years; body mass, 77.1 ± 8.3 kg; maximum oxygen consumption [VO2 max], 63.0 ± 4.8 mlVkg/min) completed an intermittent treadmill protocol replicating the activity profile of match Play. Before exercise and at 15-minute intervals, each player completed 1 of 2 randomized isokinetic dynamometer protocols. The first protocol quantified peak concentric knee extensor and flexor torque, while the second quantified peak concentric and eccentric knee flexor torque at isokinetic speeds of 180, 300, and 60 deg/s (3.14, 5.25, and 1.05 rad/s) with 5 repetitions at each speed. Results Concentric knee extensor and flexor peak torque were maintained throughout the duration of the exercise protocol, irrespective of movement speed. However, peak eccentric knee flexor torques at the end of the game (T300eccH105 = 127 ± 25 N.m) and at the end of the passive half-time interval (T300eccH60 = 133 ± 32 N.m) were significantly reduced relative to the first 15 minutes (T300eccH00 = 167 ± 35 N·m, P < .01; T300ecoH15 = 161 ± 35 N·m, P = .02). Conclusion Eccentric knee flexor strength decreases as a function of time and after the half-time interval. Clinical Relevance This suggests a greater risk of injuries at these specific times, especially for explosive movements, in accord with epidemiological observations.

Soccer fatigue, sprinting and hamstring injury risk.

The aim of this study was to investigate the effect of a multi-directional soccer-specific fatigue protocol on sprinting kinematics in relation to hamstring injury risk. Nine semi-professional soccer players (Mean +/- SD: Age: 21.3 +/- 2.9 year; Height 185.0 +/- 8.7 cm; Body Mass 81.6 +/- 6.7 kg) completed the SAFT(90); a multi-directional, intermittent 90 min exercise protocol representative of soccer match-play. The 10m sprint times and three-dimensional kinematic data were recorded using a high-speed motion capture system (Qualisys Track Manager) every 15 min during the SAFT(90). A significant time dependent increase was observed in sprint time during the SAFT(90) (P<0.01) with a corresponding significant decrease in stride length (P<0.01). Analysis of the kinematic sprint data revealed significantly reduced combined maximal hip flexion and knee extension angle, indicating reduced hamstring length, between pre-exercise and half-time (P<0.01) and pre-exercise and full-time (P<0.05). These findings revealed that the SAFT(90) produced time dependent impairments in sprinting performance and kinematics of technique which may result from shorter hamstring muscle length. Alterations in sprinting technique may have implications for the increased predisposition to hamstring strain injury during the latter stages of soccer match-play.

Soccer-Specific Fatigue and Eccentric Hamstrings Muscle Strength

CONTEXT Epidemiologic findings of higher incidences of hamstrings muscle strains during the latter stages of soccer match play have been attributed to fatigue. OBJECTIVE To investigate the influence of soccer-specific fatigue on the peak eccentric torque of the knee flexor muscles. DESIGN Descriptive laboratory study. SETTING Controlled laboratory environment. PATIENTS OR OTHER PARTICIPANTS Ten male professional soccer players (age = 24.7 +/- 4.4 years, mass = 77.1 +/- 8.3 kg, Vo(2max) = 63.0 +/- 4.8 mL x kg(-1) x min(-1)). INTERVENTION(S) Participants completed an intermittent treadmill protocol replicating the activity profile of soccer match play, with a passive halftime interval. Before exercise and at 15-minute intervals, each player completed isokinetic dynamometer trials. MAIN OUTCOME MEASURE(S) Peak eccentric knee flexor torque was quantified at isokinetic speeds of 180 degrees x s(-1), 300 degrees x s(-1), and 60 degrees x s(-1), with 5 repetitions at each speed. RESULTS Peak eccentric knee flexor torque at the end of the game (T(300eccH105) = 127 +/- 25 Nm) and at the end of the passive halftime interval (T(300eccH60) = 133 +/- 32 Nm) was reduced relative to T(300eccH00) (167 +/- 35 Nm, P < .01) and T(300eccH15) (161 +/- 35 Nm, P = .02). CONCLUSIONS Eccentric hamstrings strength decreased as a function of time and after the halftime interval. This finding indicates a greater risk of injuries at these specific times, especially for explosive movements, in accordance with epidemiologic observations. Incorporating eccentric knee flexor exercises into resistance training sessions that follow soccer-specific conditioning is warranted to try to reduce the incidence or recurrence of hamstrings strains.

Physiological and mechanical response to soccer-specific intermittent activity and steady-state activity

The aim of this study was to quantify response to a soccer-specific intermittent (INT) treadmill protocol based on notational analysis of match-play. Ten male semiprofessional football players (age 24.7 ± 4.4 yr, body mass 77.1 ± 8.3 kg, VO2max 63.0 ± 4.8 ml·kg·min−1) completed the 90 minute INT protocol and a steady-state (SS) protocol eliciting the same distance covered. Physiological (heart rate [HR], ratings of perceived exertion [RPE], blood lactate concentration, salivary cortisol concentration) and mechanical (electromyography [EMG] of biceps femoris and rectus femoris) responses were obtained at 15 minute intervals throughout each protocol. The physiological and mechanical responses were typically greater during the INT protocol than during the SS protocol, tending to increase as a function of exercise duration. The INT activity profile induces cumulative mechanical load on the musculoskeletal system. The increased incidence of injury toward the latter stages of match-play is attributed to compromised movement mechanics, rather than physiological strain.

Instructions to adopt an external focus enhance muscular endurance.

Abstract The influence of internal (movement focus) and external (outcome focus) attentional-focusing instructions on muscular endurance were investigated using three exercise protocols with experienced exercisers. Twenty-three participants completed a maximal repetition, assisted bench-press test on a Smiths machine. An external focus of attention resulted in significant (p < .05) improvements in performance compared to the internal focus of attention, but not the control condition. Seventeen participants completed repetitions to failure at 75% 1-RM on free bench-press and squat exercises. In both tasks, externally focused instructions resulted in significantly greater repetitions to failure than control and internal focus conditions (p < .05). These results support previous research showing beneficial effects of externally focused instructions on movement efficiency.

Effect of timing of eccentric hamstring strengthening exercises during soccer training: implications for muscle fatigability

Small, K, McNaughton, L, Greig, M, and Lovell, R. Effect of timing of eccentric hamstring strengthening exercises during soccer training: implications for muscle fatigability. J Strength Cond Res 23(4): 1077-1083, 2009-The purpose of this study was to examine the effects of a field-based injury prevention exercise on eccentric hamstring strength during simulated soccer match play. Sixteen semiprofessional soccer players (age 21.3 ± 2.9 years; height 185.0 ± 8.7 cm; body mass 81.6 ± 6.7 kg) completed the Soccer-specific Aerobic Field Test (SAFT90), a multidirectional 90-minute exercise protocol representative of soccer match play. Subjects performed 3 maximal dominant-limb isokinetic contractions at 120°·s−1 for concentric knee extensors (conQ) and flexors (conH), and eccentric knee flexors (eccH) before SAFT90 (t0), at half-time (t45), and immediately after the SAFT90 (t105). After baseline testing, subjects were divided into 2 groups, either performing Nordic hamstring eccentric strengthening exercises during the cool-down (CD) or warm-up (WU) of twice-weekly training sessions. After an 8-week intervention program, the baseline testing was repeated. The WU group displayed a significant increase postintervention in eccH gravity-corrected peak torque (PT) and the functional eccH:conQ ratio at t0 (p < 0.01), a significantly greater improvement compared with CD group (p < 0.05). Conversely, the CD group displayed a significant increase in both eccH PT and the functional eccH:conQ ratio postintervention at t45 (p < 0.05) and at t105 (p < 0.05), which were significantly greater increases compared with the WU group (p < 0.05). These findings indicate that the training intervention had a time-dependent beneficial effect on eccentric hamstring strength and that strength training conducted posttraining significantly reduced the negative influence of fatigue.

The influence of soccer-specific activity on the kinematics of an agility sprint

Abstract The aim of this study was to investigate the influence of soccer-specific fatigue on the kinematics of an agility sprint. Ten male professional soccer players (age 24.7±4.4 years, body mass 77.1±8.3 kg) completed an intermittent treadmill protocol replicating the activity profile of match-play, comprising two 45-min halves separated by a 15-min passive half-time interval. Pre-exercise and at 15-min intervals each player completed an agility sprint that consisted of a 180° cutting manoeuvre. Knee joint kinematics in the frontal and sagittal planes were determined for both the support and turning leg using a nine-camera automated motion analysis system operating at 200 Hz. During the penultimate foot contact, knee kinematics were characterized by joint flexion and increased varus alignment. Knee flexion at touchdown decreased significantly (P<0.05) as a function of exercise duration from 57.4±15.5° before exercise to 37.0±5.9° at the end of the second half. The range of joint movement during the knee flexion phase increased significantly during the first half (T 45=66.6±18.2°) and remained elevated during the second half (T 75=66.4±18.1°; T 90=65.7±20.4°; T 105=70.2±19.4°) relative to pre-exercise values (51.8±18.8°). During the final foot contact, knee kinematics were also characterized by flexion and increased varus alignment. Knee flexion at touchdown decreased during each half, with the knee angle at the end of the first half (30.6±7.0°) significantly (P=0.02) straighter than before exercise (39.5±6.3°), and significantly straighter at the end of the second half (30.2±2.9°) than after the half-time interval (37.7±7.8°) or before exercise. The range of knee flexion during ground contact increased significantly during each half. The range of knee varus during flexion changed from a varus displacement during the first 15 min to a valgus displacement thereafter. Peak valgus observed at the end of each half (T 45=4.7±7.9°; T 105=6.9±7.4°) was significantly (P<0.05) greater than before exercise. The range of valgus movement during knee extension was greatest following the passive half-time interval (T 60=6.2±7.3°), and tended to increase throughout the second half. Prolonged exposure to soccer-specific intermittent exercise therefore induced changes in knee kinematics that may have implications for injury incidence. The increased varus alignment and time-dependent decrease in knee flexion at touchdown represent two potential mechanisms for increased injury risk.

Speed dependant influence of attentional focusing instructions on force production and muscular activity during isokinetic elbow flexions.

This experiment assessed the influence of internal (movement) or external (outcome) attentional focusing instructions on force production and muscular activity at different movement speeds. Twenty five participants completed 10 reps of single arm elbow flexions on an isokinetic dynamometer at speeds of 60°, 180° and 300°s(-1) under three conditions (control trial, followed by counterbalanced internal and external focus trials). EMG activity of the biceps brachii and net joint elbow flexor torque were measured. An external focus was associated with significantly lower EMG at all speeds when compared to an internal focus. However, an external focus resulted in greater torque production only at 60°s(-1) when compared to an internal focus. These findings suggest that movement speed may influence the efficacy of different attentional focusing instructions, with implications for the instruction of movements in sport, exercise and rehabilitation settings.