Philip R. Hayes

The effect of two plyometric training techniques on muscular power and agility in youth soccer players

Thomas, K, French, D, and Hayes, PR. The effect of two plyometric training techniques on muscular power and agility in youth soccer players. J Strength Cond Res 23(1): 332-335, 2009-The aim of this study was to compare the effects of two plyometric training techniques on power and agility in youth soccer players. Twelve males from a semiprofessional football clubs academy (age = 17.3 ± 0.4 years, stature = 177.9 ± 5.1 cm, mass = 68.7 ± 5.6 kg) were randomly assigned to 6 weeks of depth jump (DJ) or countermovement jump (CMJ) training twice weekly. Participants in the DJ group performed drop jumps with instructions to minimize ground-contact time while maximizing height. Participants in the CMJ group performed jumps from a standing start position with instructions to gain maximum jump height. Posttraining, both groups experienced improvements in vertical jump height (p < 0.05) and agility time (p < 0.05) and no change in sprint performance (p > 0.05). There were no differences between the treatment groups (p > 0.05). The study concludes that both DJ and CMJ plyometrics are worthwhile training activities for improving power and agility in youth soccer players.

Acute milk-based protein–CHO supplementation attenuates exercise-induced muscle damage

Exercise-induced muscle damage (EIMD) leads to the degradation of protein structures within the muscle. This may subsequently lead to decrements in muscle performance and increases in intramuscular enzymes and delayed-onset muscle soreness (DOMS). Milk, which provides protein and carbohydrate (CHO), may lead to the attenuation of protein degradation and (or) an increase in protein synthesis that would limit the consequential effects of EIMD. This study examined the effects of acute milk and milk-based protein-CHO (CHO-P) supplementation on attenuating EIMD. Four independent groups of 6 healthy males consumed water (CON), CHO sports drink, milk-based CHO-P or milk (M), post EIMD. DOMS, isokinetic muscle performance, creatine kinase (CK), and myoglobin (Mb) were assessed immediately before and 24 and 48 h after EIMD. DOMS was not significantly different (p > 0.05) between groups at any time point. Peak torque (dominant) was significantly higher (p < 0.05) 48 h after CHO-P compared with CHO and CON, and M compared with CHO. Total work of the set (dominant) was significantly higher (p < 0.05) 48 h after CHO-P and M compared with CHO and CON. CK was significantly lower (p < 0.05) 48 h after CHO-P and M compared with CHO. Mb was significantly lower (p < 0.05) 48 h after CHO-P compared with CHO. At 48 h post-EIMD, milk and milk-based protein-CHO supplementation resulted in the attenuation of decreases in isokinetic muscle performance and increases in CK and Mb.

Diminutions of acceleration and deceleration output during professional football match play

OBJECTIVES This study examined distances covered at low (1-2 ms(-2)), moderate (2-3 ms(-2)) and high (>3 ms(-2)) acceleration (L(ACC), M(ACC) and H(ACC) respectively) and deceleration (L(DEC), M(DEC), and H(DEC) respectively) during competitive football games. Temporal and transient patterns of acceleration and deceleration were also examined. DESIGN Observational, repeated measures. METHODS Thirty-six professional male professional footballers were monitored using a 10 Hz non-differential global positioning system (NdGPS). Match data was organised into six 15 min periods (P1: 1-15 min, P2: 16-30 min, P3: 31-45 min, P4: 46-60 min, P5: 61-75 min, and P6: 76-90 min) for analysis of temporal patterns, and into eighteen 5 min periods for analysis of transient patterns. ANOVA with Bonferroni post hoc tests were used to identify significant (p<0.05) differences between periods. RESULTS Distance covered at L(ACC), M(ACC), H(ACC), L(DEC), M(DEC), and H(DEC) was 424±75 m, 242±25 m, 178±38 m, 365±54 m, 210±23 m and 162±29 m respectively. Between period decrements ranged from 8.0% to 13.2% from P1 to P3, 9.2% to 16.3% from P4 to P6, and from 14.9% to 21.0% from P1 to P6. Following PEAK H(ACC) (148% of mean 5 min H(ACC)), H(ACC) at 5POST was 10.4% lower than mean (p<0.01). CONCLUSIONS Time-dependent reductions in distances covered suggest that acceleration and deceleration capability are acutely compromised during match play. Further, the occurrence of transient fatigue may be supported by the findings that HACC and HDEC performance following PEAK was approximately 10% lower than mean values.

The acceleration dependent validity and reliability of 10 Hz GPS

OBJECTIVES To examine the validity and inter-unit reliability of 10 Hz GPS for measuring instantaneous velocity during maximal accelerations. DESIGN Experimental. METHODS Two 10 Hz GPS devices secured to a sliding platform mounted on a custom built monorail were towed whilst sprinting maximally over 10 m. Displacement of GPS devices was measured using a laser sampling at 2000 Hz, from which velocity and mean acceleration were derived. Velocity data was pooled into acceleration thresholds according to mean acceleration. Agreement between laser and GPS measures of instantaneous velocity within each acceleration threshold was examined using least squares linear regression and Bland-Altman limits of agreement (LOA). Inter-unit reliability was expressed as typical error (TE) and a Pearson correlation coefficient. RESULTS Mean bias ± 95% LOA during accelerations of 0-0.99 ms(-2) was 0.12 ± 0.27 ms(-1), decreasing to -0.40 ± 0.67 ms(-1) during accelerations >4 ms(-2). Standard error of the estimate ± 95% CI (SEE) increased from 0.12 ± 0.02 ms(-1) during accelerations of 0-0.99 ms(-2) to 0.32 ± 0.06 ms(-1) during accelerations >4 ms(-2). TE increased from 0.05 ± 0.01 to 0.12 ± 0.01 ms(-1) during accelerations of 0-0.99 ms(-2) and >4 ms(-2) respectively. CONCLUSION The validity and reliability of 10 Hz GPS for the measurement of instantaneous velocity has been shown to be inversely related to acceleration. Those using 10 Hz GPS should be aware that during accelerations of over 4 ms(-2), accuracy is compromised.

Effect of milk-based carbohydrate-protein supplement timing on the attenuation of exercise-induced muscle damage.

Exercise-induced muscle damage (EIMD) leads to decrements in muscle performance and increases in intramuscular enzymes measured in the plasma, and to delayed onset of muscle soreness (DOMS), partly due to the activation of degradative pathways. It has been shown that milk-based carbohydrate-protein (CHO-P) can limit changes in markers of EIMD, possibly by attenuating protein degradation and (or) increasing protein synthesis. However, the timing of supplementation has received limited attention, and this may alter the response. This study examined the effects of acute milk-based CHO-P supplementation timing on the attenuation of EIMD. Four independent matched groups of 8 healthy males consumed milk-based CHO-P before (PRE), immediately after (POST), or 24 h after (TWENTY-FOUR) muscle-damaging exercise. Active DOMS, isokinetic muscle performance, reactive strength index (RSI), and creatine kinase (CK) were assessed immediately before and 24, 48, and 72 h after EIMD. POST and TWENTY-FOUR demonstrated a benefit in limiting changes in active DOMS, peak torque, and RSI over 48 h, compared with PRE. PRE showed a possible benefit in reducing increases in CK over 48 h and limiting changes in other variables over 72 h. Consuming milk-based CHO-P after muscle-damaging exercise is more beneficial in attenuating decreases in muscle performance and increases in active DOMS at 48 h than ingestion prior to exercise.

Pre-exercise stretching does not impact upon running economy.

Pre-exercise stretching has been widely reported to reduce performance in tasks requiring maximal or near-maximal force or torque. The purpose of this study was to compare the effects of 3 different pre-exercise stretching routines on running economy. Seven competitive male middle and long-distance runners (mean ± SD) age: 32.5 ± 7.7 years; height: 175.0 ± 8.8 cm; mass: 67.8 ± 8.6 kg; &OV0622;O2max: 66.8 ± 7.0 ml·kg−1·min−1) volunteered to participate in this study. Each participant completed 4 different pre-exercise conditions: (a) a control condition, (b) static stretching, (c) progressive static stretching, and (d) dynamic stretching. Each stretching routine consisted of 2 − 30-second stretches for each of 5 exercises. Dependent variables measured were sit and reach test before and after each pre-exercise routine, running economy (ml·kg−1·km−1), and steady-state oxygen uptake (ml·kg−1·min−1), which were measured during the final 3 minutes of a 10-minute run below lactate threshold. All 3 stretching routines resulted in an increase in the range of movement (p = 0.008). There was no change in either running economy (p = 0.915) or steady-state &OV0622;O2 (p = 0.943). The lack of change in running economy was most likely because it was assessed after a period of submaximal running, which may have masked any effects from the stretching protocols. Previously reported reductions in performance have been attributed to reduced motor unit activation, presumably IIX. In this study, these motor units were likely not to have been recruited; this may explain the unimpaired performance. This study suggests that pre-exercise stretching has no impact upon running economy or submaximal exercise oxygen cost.

The relationships between local muscular endurance and kinematic changes during a run to exhaustion at vVO2max.

A recent study suggested that runners who maintain a stable running style are able to run for longer at vVO2max velocity (vVO2max). This may be because of the capacity of various muscle groups to maintain their functions despite the onset of fatigue. The purpose of this study was to examine the relationship between local muscular endurance of both the hip and knee extensor and flexor muscle groups and the kinematic changes during a run to exhaustion at vVO2max. Six subelite runners (age 24.2 ± 4.2) participated in this study; they were considered as a homogeneous group based upon their vVO2max scores (coeffeicient of variation = 3.9%). They performed an incremental protocol to determine vVO2max, a series of isokinetic tests to determine the local muscular endurance of both knee and hip flexors and extensors, and a run to exhaustion at vVO2max. The change in kinematic variables between the beginning and the end of the run were correlated with the measures of muscular endurance. Several statistically significant negative correlations emerged between the change in stride length and concentric hip extension (HEcon), r = 20.934; eccentric hip extension (HEecc), r = 20.818; eccentric knee flexion (KFecc), r = 20.957; and change in maximum hip extension (D max HE), r = 20.857; and D max HE with HEcon, r = 20.846. We concluded that the local muscular endurance of both HEcon and KFecc are important in maintaining a stable running style.

The effect of proprioceptive neuromuscular facilitation and static stretch training on running mechanics.

Caplan, N, Rogers, R, Parr, MK, and Hayes, PR. The effect of proprioceptive neuromuscular facilitation and static stretch training on running mechanics. J Strength Cond Res 23(4): 1175-1180, 2009-There is a long-standing belief that increased range of movement (RoM) at the hip or knee will improve running mechanics; however, few studies have examined the effect of such an increase in RoM. The aim of this study was to determine the influence of 2 methods of stretch training (static and proprioceptive neuromuscular facilitation [PNF]) on high-velocity running. Eighteen rugby league players were assessed for maximum sprinting velocity. They were randomly allocated into 2 stretch training groups: PNF or static. Each group trained their hamstrings 4 d·w−1 for 5 weeks. Pre- and posttraining subjects were videoed while running at 80% of maximum velocity. The video was digitized to identify biomechanical changes in hip flexion (HF), knee extension (KE), stride length (SL), stride rate (SR), and contact time (tc). Stretch training resulted in gains (p < 0.05) in HF for the static stretch (SS) (4.9%) and PNF (7.6%) groups. There were reductions in KE (p < 0.05) for SS (1.0%) and PNF (1.6%) groups. Stride mechanics were also altered after training. There were increases in SL (p < 0.05) for SS (7.1%) and PNF (9.1%) and a concomitant reduction in SR (p < 0.05) for SS (1.9%) and PNF (4.3%). No changes were observed in tc in either group. In conclusion, both SS and PNF training improved HF RoM and running mechanics during high-velocity running. These findings suggest that stretch training undertaken at the end of regular training is effective in changing running mechanics.

A mathematical model for quantifying training

A systems modelling approach has been used to quantify the dose-response nature of training. Considerable attention has been focused on the modelling process with little work on the determination of the training impulse (TRIMP) scores. Currently, the methods employed to calculate TRIMPs are subject to various limitations including the use of generic ordinal category or exponential weighting factors for higher exercise intensities. These weightings are necessary to prevent excessively high scores from long duration, low intensity bouts of exercise. We propose a new method to calculate TRIMP scores based upon a whole body bioenergetic model. Our method is individual specific, removing many of the previous limitations. Furthermore, this model could enable a greater comparison of continuous and interval training methods. This model takes into account the length of repetition(s), concentration of the interval session and mode of recovery. This approach, while requiring further research, offers a potential improvement in the accuracy of training load calculations.

The effect of a carbohydrate-caffeine sports drink on simulated golf performance

A round of golf lasts approximately 4 h, during which time homeostasis could be challenged through either hypoglycemia or hypohydration. This might result in impaired motor skill or cognitive performance. Given the high cognitive demand of putting and the potential fatiguing effects from prolonged walking, the combination of a caffeine and carbohydrate drink could be beneficial in offsetting hypoglycemia and hypohydration. This study used a laboratory-simulated round of golf to examine the effect of an isotonic carbohydrate and caffeine sports drink on putting performance during a round of golf. After institutional ethics approval, 20 male golfers (mean +/- standard deviation: age 23 +/- 4 years, stature 176.4 +/- 5.6 cm, mass 72.8 +/- 17.4 kg, handicap 15 +/- 4, daily caffeine consumption 157.3 +/- 47.2 mg) consumed either an isotonic sports drink containing caffeine (6.4 g carbohydrate and 16 mg caffeine per 100 mL) or a no-energy, flavour-matched placebo drink in a double-blind, randomized, counter-balanced crossover design . Drinks were consumed preround (5 mL.kg-1 body mass (BM)) and at holes 6 and 12 (2.5 mL.kg-1 BM). Participants therefore consumed 1.6 mg.kg-1 BM of caffeine and 0.64 g.kg-1 BM of carbohydrate throughout the trial. Five and 2 m putting performance were assessed at each hole. Self-rated mood assessments were carried out every third hole. Putting performance over 5 m and 2 m and self-rated scores for alertness and relaxation showed a main effect for drink (p < 0.05). Ratings of mental fatigue and tiredness significantly increased during the round (p < 0.001). In experienced golfers, the consumption of an isotonic carbohydrate sports drink containing caffeine prior to and during a round of golf improved putting performance and increased feelings of alertness.