• Contribution of muscular strength in cardiorespiratory fitness tests.

      Flouris, Andreas D.; Metsios, Giorgos S.; Koutedakis, Yiannis (Edizioni Minerva Medica, 2006)
      Reports from laboratory-based studies have revealed a relationship between resistance training and endurance performance in both trained and untrained individuals. The purpose of the present study was to investigate the contribution of lower extremity muscular strength levels in performing cardiorespiratory fitness tests in laboratory, as well as field-based settings. Within 2 weeks 38 healthy males (age 21.6±2.5 years, body mass index-BMI-24.4±2.2) performed three maximal oxygen uptake (VO^sub 2max^) assessments using the 20 m multistage shuttle run test (MSR), the 20 m square shuttle run test (SSR), and a maximal treadmill test (MT) to exhaustion. Data were also obtained from knee flexion and extension isokinetic dynamometry at 60^sub °0·s-1^. MSR performance correlated with the peak torque generated from both legs at r=0.63 (P<0.001 ). The equivalent for SSR was significant at r=0.44 (P<0.05), while MT demonstrated a non-significant positive correlation coefficient (r=0.34, P>0.05). Stepwise regression analyses revealed that the inclusion of leg strength parameters increased the coefficient of determination by 9% (P<0.001) and 4% (P<0.05) in the MSR and SSR, respectively. The MT model was not significantly associated with any of the isokinetic indices studied. Although moderately significant, the present coefficients suggest that performance in the present field-based cardiorespiratory fitness tasks is affected to a certain extent by lower extremity muscular strength. The latter also demonstrates a positive relationship with laboratory-based performance.
    • Evaluation of knee peak torque in athletic and sedentary children.

      Deighan, Martine A.; Nevill, Alan M.; Maffulli, Nicola; Cheng, Jack C. Y.; Gleeson, Nigel (Ekin Medical Publishing, 2009)
      Objectives: We examined the influence of sex, level of activity, and pubertal status on knee extension (Ext) and flexion(Fl) peak torque (PT) in children using an allometric modeling approach. Methods: A total of 140 students (67 males, 73 females)aged 12/13 years were enrolled from a Hong Kong junior high school, whose curricula were based on physical education (n=69) or arts (n=71). Isokinetic concentric Ext and Fl PT of the dominant leg was assessed at 1.04 rad/sec using a Cybex II+ dynamometer and body mass,stature, and pubertal stage were measured. A repeated-measures ANOVA test was performed on absolute PT data with muscle action (Ext and Fl) as a within-subject factor and between-subject factors including sex, group,and pubertal stage. To assess the effects on body sizeadjusted PT, linear ANCOVA and log-linear ANCOVA techniques were used with body mass and stature taken as covariates. Results: Peak torque was significantly greater in boys compared to girls, and in the physical education group compared to the arts group. When PT was adjusted for differences in body size, there was a greater difference in PT between girls in the two groups compared to boys, and there was a significant effect of pubertal stage. Allometric analysis showed that PT was influenced more by stature than body mass, and PT increased at a greater rate than body size (both p<0.01). Conclusion: There may be a need for a physical activity intervention in sedentary 12/13 year old girls. Peak torque appears to increase disproportionately to body size. This may result from a greater increase in leg muscle mass relative to body mass
    • Hormonal factors in the development of differences in strength between boys and girls during adolescence: a longitudinal study.

      Round, J. M.; Jones, David A.; Honour, J. W.; Nevill, Alan M. (Taylor & Francis for the Society for the Study of Human Biology, 1999)
      The development of elbow flexor (biceps) and knee extensor (quadriceps) strength has been followed in a mixed longitudinal study of 50 boys and 50 girls from the age of 8 to 17 years. Sex differences in strength emerged at the time of peak height velocity and were especially marked for the biceps. Data for individual children were aligned to the time of peak height velocity and associations between strength, height, weight and circulating testosterone were investigated using multi-level modelling. The results show that, for girls, quadriceps strength is proportional to height and weight while for boys there is an additional factor which can be fully attributed to increasing levels of testosterone. Testosterone is important in explaining differences in biceps strength between the sexes but an additional factor is also required. It is suggested that, in addition to a direct effect on muscle, testosterone could have a second indirect action on biceps strength by promoting growth in length of the humerus as part of the general development of the male upper limb girdle.
    • Modelling the relationship between isokinetic muscle strength and sprint running performance.

      Dowson, M. N.; Nevill, Mary E.; Lakomy, H. K.; Nevill, Alan M.; Hazeldine, R. J. (London: Taylor & Francis Ltd., 1998)
      Muscle strength is thought to be a major factor in athletic success. However, the relationship between muscle strength and sprint performance has received little attention. The aim of this study was to examine the relationship in elite performers of isokinetic muscle strength across three lower limb joints and sprinting performance, including the use of theoretical models. Eight rugby players, eight track sprinters and eight competitive sportsmen, all elite national or regional competitors, performed sprints over 15 m and 35 m with times recorded over 0-15 m and 30-35 m. Isokinetic torque was measured at the knee, hip and ankle joints at low (1.05 rad s(-1)), intermediate (2.09 or 2.62 rad s(-1)) and high (3.14 or 4.19 rad s(-1)) speeds during concentric and eccentric muscle actions. Using linear regression and expressing sprint performance as time, the strongest relationship, for the joint actions and speeds tested, was between concentric knee extension at 4.19 rad s(-1) and sprint performance (0-15 m times: r=-0.518, P< 0.01; 30-35 m times: r=-0.688, P< 0.01). These relationships were improved for 0-15 m, but not for 30-35 m, by expressing torque relative to body mass (0-15 m times: r=-0.581; 30-35 m times: r=-0.659). When 0-15 m performance was expressed as acceleration rather than time, the correlation was improved slightly (r=0.590). However, when the data (0-15 m times) were fitted to the allometric force model proposed by Gunther, 77% of the variance in concentric knee extension torque at 4.19 rad s(-1) could be explained by 0-15 m times, limb length (knee to buttocks) and body mass. The fitted parameters were similar to those from the theoretical model. These findings suggest that the relationship between isokinetic muscle strength and sprint performance over 0-15 m (during the acceleration phase) is improved by taking limb length and body mass into account.
    • Prolonged depression of knee-extensor torque complexity following eccentric exercise

      Pethick, Jamie; Whiteaway, Katherine; Winter, Samantha L; Burnley, Mark; Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, UK. (Wiley, 2018-11-28)
      Neuromuscular fatigue reduces the temporal structure, or complexity, of muscle torque output. Exercise-induced muscle damage reduces muscle torque output for considerably longer than high-intensity fatiguing contractions. We hypothesized that muscle-damaging eccentric exercise would lead to a persistent decrease in torque complexity, whereas fatiguing exercise would not. Ten healthy participants performed five isometric contractions (6 s contraction, 4 s rest) at 50% maximal voluntary contraction (MVC) before, immediately after and 10, 30 and 60 min and 24 h after eccentric (muscle-damaging) and isometric (fatiguing) exercise. These contractions were also repeated 48 h and 1 week after eccentric exercise. Torque and surface EMG signals were sampled throughout each test. Complexity and fractal scaling were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis α exponent (DFA α). Global, central and peripheral perturbations were quantified using MVCs with femoral nerve stimulation. Complexity decreased after both eccentric [ApEn, mean (SD), from 0.39 (0.10) to 0.20 (0.12), P < 0.001] and isometric exercise [from 0.41 (0.13) to 0.09 (0.04); P < 0.001]. After eccentric exercise, ApEn and DFA α required 24 h to recover to baseline levels, but after isometric exercise they required only 10 min. The MVC torque remained reduced [from 233.6 (74.2) to 187.5 (64.7) N m] 48 h after eccentric exercise, with such changes evident only up to 60 min after isometric exercise [MVC torque, from 246.1 (77.2) to 217.9 (71.8) N m]. The prolonged depression in maximal muscle torque output is therefore accompanied by a prolonged reduction in torque complexity.
    • Recovery kinetics of knee flexor and extensor strength after a football match

      Draganidis, D; Chatzinikolaou, A; Avloniti, Alexandra; Barbero-Álvarez, JC; Mohr, M; Malliou, P; Gourgoulis, V; Deli, CK; Douroudos, II; Margonis, K; et al. (Public Library of Science (PLoS), 2015-06-04)
      We examined the temporal changes of isokinetic strength performance of knee flexor (KF) and extensor (KE) strength after a football match. Players were randomly assigned to a control (N = 14, participated only in measurements and practices) or an experimental group (N = 20, participated also in a football match). Participants trained daily during the two days after the match. Match and training overload was monitored with GPS devices. Venous blood was sampled and muscle damage was assessed pre-match, post-match and at 12h, 36h and 60h post-match. Isometric strength as well as eccentric and concentric peak torque of knee flexors and extensors in both limbs (dominant and non-dominant) were measured on an isokinetic dynamometer at baseline and at 12h, 36h and 60h after the match. Functional (KFecc/KEcon) and conventional (KFcon/KEcon) ratios were then calculated. Only eccentric peak torque of knee flexors declined at 60h after the match in the control group. In the experimental group: a) isometric strength of knee extensors and knee flexors declined (P<0.05) at 12h (both limbs) and 36h (dominant limb only), b) eccentric and concentric peak torque of knee extensors and flexors declined (P<0.05) in both limbs for 36h at 60°/s and for 60h at 180°/s with eccentric peak torque of knee flexors demonstrating a greater (P<0.05) reduction than concentric peak torque, c) strength deterioration was greater (P<0.05) at 180°/s and in dominant limb, d) the functional ratio was more sensitive to match-induced fatigue demonstrating a more prolonged decline. Discriminant and regression analysis revealed that strength deterioration and recovery may be related to the amount of eccentric actions performed during the match and athletes' football-specific conditioning. Our data suggest that recovery kinetics of knee flexor and extensor strength after a football match demonstrate strength, limb and velocity specificity and may depend on match physical overload and players' physical conditioning level.
    • Thigh Peak Torques and Lower-Body Injuries in Dancers

      Koutedakis, Yiannis; Khaloula, M.; Pacy, P.; Murphy, Marie H.; Dunbar, G. (International Association for Dance Medicine & Science, 1997)
      The purpose of this study was to identify possible relationships between the sum of knee flexion and extension peak torques and the severity of lower-body injuries in professional dancers. Twenty male (age 26.6 (+/- 6.0) years) and 22 female (age 27.1 (+/- 5.4) years) ballet and contemporary dancers reported one or more low-back, pelvis, leg, knee and foot injuries. The severity of injuries was established by recording the days off dance activities. Subjects were then monitored on a Cybex II or a KIN-CON isokinetic dynamometer. Knee flexion and extension peak torques were obtained bilaterally during three normal contractions at the velocities of 1.04 and 4.19 rad/sec. No musculoskeletal injuries were reported at the time of data collection. At 1.04 rad/sec, results revealed significant correlation coefficients between relative thigh peak torques - expressed in Nm/kg fat free mass (FFM) - and prevalence of low extremity injuries. These findings suggest that the lower thethigh-power output, the greater the degree of injury. Female dancers demonstrated higher correlation coefficients (r = -0.70; p < 0.005) than their male counterparts (r = -0.61; p < 0.01). However, no such correlations were found at the angular velocity of 4.19 rad/sec, nor when low-back injuries and thigh-power outputs were considered at both velocities. The main conclusions are: a ) low thigh power outputs are likely to be associated with the severity of low extremity injuries, and b) such relationships are better identified at lower compared to higher isokinetic velocities