The effects of injury prevention warm-up programmes on knee strength in male soccer players

The study investigates the effects of the 11+ and HarmoKnee injury prevention programmes on knee strength in male soccer players. Under-21-year-old players (n=36) were divided equally into: the 11+, HarmoKnee and control groups. The programmes were performed for 24 sessions (20-25 min each). The hamstrings and quadriceps strength were measured bilaterally at 60°·s^-1, 180°·s^-1 and 300°·s^-1. The concentric quadriceps peak torque (PT) of the 11+ increased by 27.7% at 300°·s^-1 in the dominant leg (p<0.05). The concentric quadriceps PT of HarmoKnee increased by 36.6%, 36.2% and 28% in the dominant leg, and by 31.3%, 31.7% and 20.05% at 60°·s^-1, 180°·s^-1 and 300°·s^-1 in the non-dominant leg respectively. In the 11+ group the concentric hamstring PT increased by 22%, 21.4% and 22.1% at 60°·s^-1, 180°·s^-1 and 300°·s^-1, respectively in the dominant leg, and by 22.3%, and 15.7% at 60°·s^-1 and 180°·s^-1, in the non-dominant leg. In the HarmoKnee group the hamstrings in the dominant leg showed an increase in PT by 32.5%, 31.3% and 14.3% at 60°·s^-1, 180°·s^-1 and 300°·s^-1, and in the non-dominant leg hamstrings PT increased by 21.1% and 19.3% at 60°·s^-1 and 180°·s^-1 respectively. The concentric hamstrings strength was significantly different between the 11+ and control groups in the dominant (p=0.01) and non-dominant legs (p=0.02). The HarmoKnee programme enhanced the concentric strength of quadriceps. The 11+ and HarmoKnee programmes are useful warm-up protocols for improving concentric hamstring strength in young professional male soccer players. The 11+ programme is more advantageous for its greater concentric hamstring strength improvement compared to the HarmoKnee programme.

Decrease of postprandial endothelial dysfunction by spice mix added to high-fat hamburger meat in men with Type 2 diabetes mellitus

AIMS

Consumption of a high-fat diet has been demonstrated to promote endothelial dysfunction, possibly through an increase in lipid peroxidation and decrease in serum nitric oxide. The present study was designed to investigate whether consumption of a hamburger cooked with a polyphenol-rich spice mixture will reduce postprandial lipid oxidation and endothelial dysfunction in men with Type 2 diabetes.

METHODS

Twenty-two subjects consumed burgers cooked with salt only (control burger) or with salt and spice mix (spice burger) in randomized order. The postprandial concentration of urinary malondialdehyde and nitrate/nitrite as well as the peripheral arterial tonometry score were determined.

RESULTS

Eighteen subjects completed the study. Postprandial serum glucose, insulin and triglyceride concentrations were similar in all subjects after control burger or spice burger consumption. Urine malondialdehyde excretion in mmol/g creatinine was reduced by 31% (P < 0.001) after consuming the spice burger compared with the control burger. Two hours after consumption of the burgers, the peripheral arterial tonometry score was significantly different between control burger consumption (-9.7 ± 21.5%) and spice burger consumption (+18.0 ± 42.4%) (P = 0.025). Mean urinary nitrate/nitrite concentrations in urine collected during the 6 h after consumption of the control burger was 9.09 ± 5.7 mmol/g creatinine, but 12.37 ± 7.00 mmol/g creatinine after the spice burger (P = 0.053).

CONCLUSION

Adding a spice mix to hamburger meat prior to cooking resulted in a reduction in urinary malondialdehyde, an increase in urinary nitrate/nitrite and improvement of postprandial endothelial dysfunction in men with Type 2 diabetes. Therefore, cooking a hamburger with a polyphenol-rich spice mixture may lead to potential cardiovascular benefits in patients with Type 2 diabetes mellitus.

Effect of various ratios of carbohydrate-protein supplementation on resistance exercise-induced muscle damage

AIM

Previous studies have indicated that exercise-induced muscle damage might be attenuated by coingestion of protein and carbohydrate supplement. The purpose of this study was to compare the effect of three various ratios of carbohydrate-protein (CHO+PRO) supplements on resistance exercise-induced muscle damage indices.

METHODS

Twenty-eight untrained male students voluntarily participated in this study and were randomly assigned to one of the four groups: 1) CHO+PRO 2:1 ratio, N.=7; 2) CHO+PRO 3:1 ratio, N.=8; 3) CHO+PRO 4:1 ratio, N.=7; 4) placebo group, N.=6. They performed a single bout of resistance exercise (whole body: 3 set×8-10 reps with 70-75% 1RM), with eccentric concentration. Every group consumed prepared CHO/PRO beverages (9% concentration, 10 mL/kg/bw-1 at different ratios) or the same amount of placebo beverage before and in 15 min intervals during exercise. Blood samples were taken before the exercise bout and also at 1 and 24 h post-exercise. In addition, muscle soreness scores were recorded before and 1, 24, and 48 h postexercise. Repeated measures ANOVA (between-within design) and Bonferroni post hoc test were used to analyze dependent measures (α=0.05).

RESULTS

Serum creatine kinase (CK) and myoglobin (Mb) increased in all groups compared with pre-exercise but the significant difference among groups was observed in 24 h postexercise, in a way that both CK and Mb levels were higher in placebo group. Muscle soreness increased for all groups from pre to postexercise, but there was not any significant difference among groups at any time point.

CONCLUSION

Findings of this study showed that CHO+PRO decreased serum CK and Mb at 24 h post exercise, but did not affect muscle soreness at any time points after exercise. Moreover, there were no significant differences between various ratios of CHO-PRO supplementation.

Oxidative stress responses in physical education students during 8 weeks aerobic training

AIM

This study aimed to evaluate responses of selected markers of oxidative stress in physical education students during aerobic training.

METHODS

Twenty male students were randomly assigned into either a control (mean+/-SD: age 23.5+/-1.4 years, height 1.72+/-0.06 m, body mass 68.9+/-5.8 kg, n=10) or an aerobic training (mean+/-SD: age 23.8+/-1.8 years, height 1.66+/-0.03 m, body mass 65.5+/-4.8 kg, n=10, 3 training sessions per week, 8 weeks, running at 75-80% of HR(max)) group. Plasma samples, collected at rest and after exercise to exhaustion before and after 8 weeks, were analysed for the determination of selected markers of oxidative stress (malondialdehyde MDA, carbonylated proteins CP, and creatine kinase CK).

RESULTS

Aerobic training caused a 10% increase in maximal oxygen consumption (VO(2max)) and a 9% increase in exercise time to exhaustion (P<0.05). The aerobic training did not significantly change (P>0.05) MDA and CP levels at rest and after exercise to exhaustion. An exhaustive exercise caused a substantial increase (P<0.05) of CK in both groups independent of treatment and time of measurement. However, aerobic training did not prevent serum CK from increasing after exercise to exhaustion (P>0.05).

CONCLUSIONS

It can be concluded that this pattern of moderate aerobic exercise training did not have any effect on oxidative stress levels in moderately trained physical education students, whereas it enhanced their functional performance and aerobic power of these physical education students.

The isolated and combined effects of selected physical activity and ibuprofen on delayed-onset muscle soreness

Delayed-onset muscle soreness refers to the skeletal muscle pain that is experienced following eccentric exercise. The aim of the present study was to examine the physiological effects of physical activity with or without ibuprofen on delayed onset muscle soreness. Forty-four non-athletic male volunteers (age 24.3 +/- 2.4 years) were randomly assigned to one of four groups: physical activity (n = 11), ibuprofen (n = 11), physical activity and ibuprofen (combination, n = 11), or control (n = 11). The physical activity programme comprised 5 min of walking and jogging, 10 min of static stretching of the hands and shoulder girdle, and 5 min of concentric movements with sub-maximal contractions. The total amount of ibuprofen consumed by a single individual was 2800 mg; this was taken from 1 h before the eccentric actions up to 48 h after it. Delayed onset muscle soreness was induced by performing 70 eccentric contractions of the biceps muscle of the non-dominant side on a modified arm curl machine. Perceived muscle soreness, maximal eccentric contraction, creatine kinase enzyme activity and elbow range of motion were assessed 1 h before and 1, 24 and 48 h after the eccentric actions. The results indicated that, after the eccentric actions, soreness increased (P < 0.001) across time in all groups, with the highest values being recorded at 24 h. At 24 and 48 h, greater soreness (P < 0.001) was observed in the control group than in the physical activity and combination groups. After the eccentric actions, creatine kinase increased and was elevated (P < 0.001) compared with baseline in all groups, with values returning to baseline in the physical activity and combination groups by 48 h. However, creatine kinase in the control and ibuprofen groups was still significantly higher than at baseline after 48 h. Creatine kinase was higher (P < 0.001) in the control group than in physical activity and combination groups at 24 and 48 h. There was also a reduction (P < 0.001) in elbow range of motion across time. This reduction in elbow range of motion was greater (P < 0.001) in the control and ibuprofen groups than in the physical activity and combination groups at 1, 24 and 48 h. The reduction in maximum eccentric contraction was greater (P < 0.001) in the control and ibuprofen groups than in the physical activity group at 24 and 48 h and the combination group at 48 h. In conclusion, the results add to our understanding of the effects of physical activity and the combination of physical activity and ibuprofen in reducing the severity of muscle soreness induced by eccentric exercise. Physical activity conducted before eccentric exercise alleviates muscle soreness. Our results indicate that physical activity with or without ibuprofen helps to prevent delayed-onset muscle soreness.

Effects of vitamin E supplementation on oxidative stress at rest and after exercise to exhaustion in athletic students

AIM

The purpose of this study is to determine the effect following exercise to exhaustion of vitamin E supplementation on oxidative stress in athletic students.

METHODS

Twenty male students voluntarily participated in the study and were randomly assigned (double blind) to either a vitamin E (daily dose of 450 mg of a-tocopherol for a period of 8 weeks) or a placebo group (took capsules containing 450 mg of lactose for 8 weeks). Before and after 8 weeks blood samples were collected at rest and after exercise to exhaustion. Oxidative stress markers were malondialdehyde (MDA), carbonylated proteins (CP) and creatine kinase (CK). Also, the effect of vitamin E on ergometer cycling time, as an example of endurance performance, was evaluated.

RESULTS

ANOVA and independent t-tests indicated that vitamin E supplementation did not significantly change (P > 0.05) MDA, CP and CK values at rest, after exercise to exhaustion, and cycling time, but plasma volume after exercise to exhaustion significantly decreased (P < 0.05).

CONCLUSIONS

Although vitamin E supplementation had no effect on exercise performance or capacity in athletic students, further investigation is required using larger numbers of subjects and measures of vitamin E before unequivocal conclusion can be stated.

Muscle fatigue induced by exercise simulating the work rate of competitive soccer

Fatigue represents a reduction in the capability of muscle to generate force. The aim of the present study was to establish the effects of exercise that simulates the work rate of competitive soccer players on the strength of the knee extensors and knee flexors. Thirteen amateur soccer players (age 23.3+/-3.9 years, height 1.78+/-0.05 m, body mass 74.8+/-3.6 kg; mean+/-s) were tested during the 2000-2001 soccer season. Muscle strength of the quadriceps and hamstrings was measured on an isokinetic dynamometer. A 90 min soccer-specific intermittent exercise protocol, incorporating a 15 min half-time intermission, was developed to provide fatiguing exercise corresponding in work rate to a game of soccer. The exercise protocol, performed on a programmable motorized treadmill, consisted of the different intensities observed during soccer match-play (e.g. walking, jogging, running, sprinting). Muscle strength was assessed before exercise, at half-time and immediately after exercise. A repeated-measures analysis of variance showed significant reductions (P < 0.001) in peak torque for both the quadriceps and hamstrings at all angular velocities (concentric: 1.05, 2.09, 5.23 rad x s(-1); eccentric: 2.09 rad x s(-1)). The peak torque of the knee extensors (KE) and knee flexors (KF) was greater before exercise [KE: 232+/-37, 182+/-34, 129+/-27, 219+/-41 N x m at 1.05, 2.09 and 5.23 rad x s(-1) (concentric) and 2.09 rad x s(-1) (eccentric), respectively; KF: 126+/-20, 112+/-19, 101+/-16, 137+/-23 N x m] than at half-time (KE: 209+/-45, 177+/-35, 125+/-36, 214+/-43 N x m; KF: 114+/-31, 102+/-20, 92+/-15, 125+/-25 N x m) and greater at half-time than after exercise (KE: 196+/-43, 167+/-35, 118+/-24, 204+/-43 N x m; KF: 104+/-25, 95+/-21, 87+/-13, 114+/-27 N x m). For the hamstrings:quadriceps ratio, significant changes were found (P < 0.05) for both legs, the ratio being greater before than after exercise. For fast:slow speed and left:right ratios, no significant changes were found. We conclude that there is a progressive reduction in muscle strength that applies across a range of functional characteristics during exercise that mimics the work rate in soccer.

Injury risk associated with playing actions during competitive soccer

OBJECTIVE

To assess the exposure of players to injury risk during English Premier League soccer matches in relation to selected factors.

METHODS

Injury risk was assessed by rating the injury potential of playing actions during competition with respect to (a) type of playing action, (b) period of the game, (c) zone of the pitch, and (d) playing either at home or away. In all, 10 games from the English Premier League 1999-2000 were chosen for analysis. A notation system was used whereby 16 soccer specific playing actions were classified into three categories: those inducing actual injury, those with a potential for injury (graded as mild, moderate, or high), and those deemed to have no potential for injury. The pitch was divided into 18 zones, and the position of each event was recorded along with time elapsed in the game, enabling six 15 minute periods to be defined.

RESULTS

Close to 18 000 actions were notated. On average (mean (SD)), 1788 (73) events (one every three seconds), 767 (99) events with injury potential (one every six seconds), and 2 (1) injuries (one every 45 minutes) per game were recorded. An overall injury incidence of 53 per 1000 playing hours was calculated. Receiving a tackle, receiving a "charge", and making a tackle were categorised as having a substantial injury risk, and goal catch, goal punch, kicking the ball, shot on goal, set kick, and heading the ball were all categorised as having a significant injury risk. All other actions were deemed low in risk. The first 15 minutes of each half contained the highest number of actions with mild injury potential, the last 15 minutes having the highest number of actions with moderate injury potential (p<0.01). The first and last 15 minutes of the game had the highest number of actions with high injury potential, although not significant. More actions with mild injury potential occurred in the goal area, and more actions with moderate and high injury potential occurred in the zone adjacent to the goal area (p<0.001). There was no significant difference between home and away with regard to injury potential.

CONCLUSIONS

Playing actions with high injury risk were linked to contesting possession. Injury risk was highest in the first and last 15 minutes of the game, reflecting the intense engagements in the opening period and the possible effect of fatigue in the closing period. Injury risk was concentrated in the areas of the pitch where possession of the ball is most vigorously contested, which were specific attacking and defending zones close to the goal. Injury potential was no greater in away matches than at home.