Biomedical subjects

Eleftherios Kellis

Publications and source records attributed to Eleftherios Kellis.

8 recordsLinked to original sources

PubMed2007

Ankle sprain injuries and risk factors in amateur soccer players during a 2-year period.

BACKGROUND: Although ankle sprains are common in soccer, the role of various risk factors in amateur soccer players is unclear. PURPOSE: To identify the incidence of ankle sprain injuries, associated time loss of participation, and risk factors during two consecutive seasons in amateur players. STUDY DESIGN: Descriptive epidemiology study. METHODS: Of 336 athletes enrolled in the study, 312 male amateur soccer players were observed during a 2-year period. Ankle sprain injury incidents, participation time loss, injury mechanisms, ankle region injured, and other risk factors were recorded in games and practice sessions using questionnaires. RESULTS: During the study 208 ankle injuries were recorded, of which 139 were ankle sprains. These led to 975 sessions lost (on average, 7 lost sessions per injury). Most incidents (80.6%) were contact injuries, occurring mostly in defenders. Injury rates were equal between games and practice, while 61.1% of injuries were observed toward the end of each half of the game (P < .05). The injury incidence rate was higher during the first 2 months of the season as opposed to the last month (P < .05). Multinomial logistic regression showed that previous ankle sprain (P < .05) is a significant predictor of ankle sprain injury. CONCLUSION: Ankle sprain injuries in amateur soccer players are primarily contact injuries, occurring mainly in defenders and during both games and practice. It appears that more injuries occur in players with previous ankle injury. Injury rates are higher toward the end of a game and chiefly occur during the first 2 months of the season.

Adult↗

PubMed2006

Hamstring antagonist moment estimation using clinically applicable models: Muscle dependency and synergy effects.

The purpose of this study was to examine whether prediction of antagonist moment (M(flx)) of the hamstrings using clinically applicable models depends on the muscles examined. Nine healthy males performed maximal isometric knee extension and flexion contractions at 0 degrees , 45 degrees and 90 degrees angles. Calibration knee flexion efforts were also performed at different levels of intensity. The resulting electromyographic (EMG) - moment curves were fitted using polynomial equations which were then used to estimate M(flx) from the antagonist EMG. Analysis of variance designs showed that the M(flx) predicted using the biceps femoris EMG was not significantly different compared with those predicted using the semitendinosus EMG data (p>0.05). Further, prediction of M(flx) using the EMG of both muscles or a combination of EMGs and architectural properties reduced estimation error but did not provide significantly different predicted values compared with the simpler single-muscle EMG - moment models (p<0.05). It appears that M(flx) prediction using the present EMG - moment model is not muscle specific. Prediction using models which combine EMG data and anatomic parameters of the hamstring muscle components yielded more accurate estimates and therefore their use to examine co-contraction levels is recommended.

Achilles Tendon↗

PubMed2006

Effects of two 4-week proprioceptive neuromuscular facilitation programs on muscle endurance, flexibility, and functional performance in women with chronic low back pain.

BACKGROUND AND PURPOSE: Improving functional performance in patients with chronic low back pain is of primary importance. The purpose of this study was to examine the effects of 2 proprioceptive neuromuscular facilitation (PNF) programs on trunk muscle endurance, flexibility, and functional performance in subjects with chronic low back pain (CLBP). SUBJECTS: Eighty-six women (40.2+/-11.9 [mean+/-SD] years of age) who had complaints of CLBP were randomly assigned to 3 groups: rhythmic stabilization training, combination of isotonic exercises, and control. METHODS: Subjects trained with each program for 4 weeks with the aim of improving trunk stability and strength. Static and dynamic trunk muscle endurance and lumbar mobility were measured before, at the end of, and 4 and 8 weeks after training. Disability and back pain intensity also were measured with the Oswestry Index. RESULTS: Multivariate analysis of variance indicated that both training groups demonstrated significant improvements in lumbar mobility (8.6%-24.1%), static and dynamic muscle endurance (23.6%-81%), and Oswestry Index (29.3%-31.8%) measurements. DISCUSSION AND CONCLUSION: Static and dynamic PNF programs may be appropriate for improving short-term trunk muscle endurance and trunk mobility in people with CLBP.

Adult↗

PubMed2005

Reliability of a practicable EMG-moment model for antagonist moment prediction.

Although the use of practicable EMG-moment models for knee joint moment prediction appears promising, the repeatability of the estimated forces remains unclear. The purpose of this study was to apply an EMG-moment model to predict the antagonist moment of the knee flexors (Mflx) during maximal isometric knee extension efforts. Nine healthy males performed maximal isometric knee extension and flexion contractions at 0 degrees , 45 degrees and 90 degrees angles with recordings of the net moment and EMG of thigh muscles. Calibration knee flexion efforts were performed at different levels of intensity and the resulting EMG-moment curves were fitted using second-order polynomials. The polynomials were then used to predict Mflx. This procedure was repeated a week after. The results indicated non-significant differences in test-retest Mflx. Intraclass correlation coefficients ranged from 0.852 to 0.912 indicating high test-retest reliability of the estimated Mflx. For isometric contractions, the present model is suitable as a method to estimate antagonist muscle moments.

Adult↗

PubMed2005

Effects of load on ground reaction force and lower limb kinematics during concentric squats.

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1 +/- 0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67 +/- 0.20 to 3.21 +/- 0.29 times body weight and increased significantly as external load increased (P < 0.05). Bar linear velocity ranged from 0.54 +/- 0.11 to 2.50 +/- 0.50 m x s(-1) and decreased significantly with increasing external load (P < 0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P < 0.05). The force-barbell velocity curves were fitted using linear models with coefficients (r2) ranging from 0.59 to 0.96. The results suggest that maximal force exertion during squat exercises is not achieved at the same position of the lower body as external load is increased. In contrast, joint velocity coordination does not change as load is increased. The force-velocity relationship was linear and independent from the set of data used for its determination.

Adult↗

PubMed2004

Knee biomechanics of the support leg in soccer kicks from three angles of approach.

PURPOSE: To examine knee joint kinematics, electromyographic (EMG) activity patterns and ground reaction forces (GRF) during an instep soccer kick from three different approaches relative to the ball. METHODS: Ten male soccer players performed maximum kicks from 0 rad (K0), 0.81 rad (K45), and 1.62 rad (K90) angle between the players' starting position and the position of the ball. GRF data and 3-D kinematics and EMG activity of the vastus medialis (VM), vastus lateralis (VL), and biceps femoris (BF) muscles of the lower leg were recorded. RESULTS: colon; Compared with K0, K90, and K45 demonstrated higher medial and posterior GRF and lower anterior GRF. K90 and K45 also demonstrated higher external rotation displacement, maximum flexion, internal rotation, abduction, and adduction velocity of the tibia relative to the femur of the support leg compared with K0 (P < 0.01). The BF EMG before and immediately after ground contact was also higher in K90 and K45 compared with K0 (P < 0.01). CONCLUSION: Soccer kicks using a high angle of approach increase the medial and posterior GRF, which is indicative of an altered stance during the kick, resulting in an altered balance. Such kicks are accompanied by significant alterations in knee joint kinematics and an increased BF activation around ground contact. Soccer kicks from an angled approach may induce significant loads to knee joint structures of the support leg.

Adult↗

PubMed2003

Antagonist moment of force during maximal knee extension in pubertal boys: effects of quadriceps fatigue.

The examination of the moment exerted by the hamstrings during maximum isokinetic knee extensor tests is useful when comparing isokinetic strength and muscle activity patterns between children and adults. The purpose of this study was to examine the effect of antagonist moment of the hamstrings on the isokinetic moment of the knee extensors in pubertal children and to determine whether this effect is altered following a fatigue task. Eighteen healthy pubertal males [age 14.3 (0.5) years] performed 34 maximal isokinetic concentric efforts of the knee extensors at 60 degrees.s(-1). The average moment of force and electromyographic (aEMG) signal of vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) at 11-30 degrees, 31-50 degrees, 51-70 degrees and 71-90 degrees of knee flexion were calculated for each repetition. The hamstrings antagonist moment was determined before and after the fatigue task by fitting the aEMG-moment relationship at different levels of muscle effort using second-degree polynomials. The percentage contribution of the antagonist moment to the resultant joint moment ranged from 7.1 % to 60.4 % throughout the range of motion, with the highest percentage observed close to full knee extension (11-30 degrees). The antagonist effect was significantly greater during concentric tests of the knee extensors compared to the corresponding eccentric tests ( p<0.05). Following the fatigue test, there was an overall decline of the resultant joint moment, but no changes in the predicted hamstrings moment were observed. These results indicate that when testing maximal knee extensor isokinetic strength in pubertal boys, activity of the hamstrings implies a reduction of the net extensor moment as compared to the isolated capacity of the knee extensors. However, this antagonist effect is not altered following the performance of an isokinetic fatigue knee extension task.

Adaptation, Physiological↗

PubMed2003

The effects of a calisthenics and a light strength training program on lower limb muscle strength and body composition in mature women.

This study evaluated and compared the effectiveness of an aerobics-calisthenics (A-CAL) and an aerobics/weight training (A-WT) programs on lower limb strength and body fat (%). Thirty-five adult women (age 42.1 +/- 5.2 years) were randomly assigned to A-CAL (n = 14), A-WT (n = 14), or a control group (n = 7). The A-CAL and A-WT trained 3 days per week for 10 weeks. Maximal bilateral isometric and isokinetic knee extension (KEXT) and flexion (KFLEX) torque, squat jump (SJ), and body fat (%) were measured before and immediately after training. The results revealed nonsignificant differences between A-CAL and A-WT (p > 0.05). Both A-CAL and A-WT improved SJ (p < 0.001). A-WT increased isometric torque of KEXT and KFLEX (p < 0.05), isokinetic torque of KFLEX (p < 0.05), and decreased body fat (%) (p < 0.05) when compared with controls. In summary, the application of a 10-week light-weight training program improved selected strength parameters of healthy women, compared with controls, but the effectiveness of the calisthenics exercises as an independent form of strength training is dubious.

Adult↗