Erika Zemková

Effects of obesity, diabetes and exercise on Fndc5 gene expression and irisin release in human skeletal muscle and adipose tissue: in vivo and in vitro studies

Considerable controversy exists regarding the role of irisin, a putative exercise‐induced myokine, in human metabolism. We therefore studied irisin and its precursor Fndc5 in obesity, type 2 diabetes and exercise. Complex clinical studies combined with cell culture work revealed that Fndc5/irisin was decreased in type 2 diabetes in vivo, but not in muscle cells in vitro, indicating that diabetes‐related factor(s) regulate Fndc5/irisin in vivo. Several attributes of type 2 diabetes, such as hyperglycaemia, triglyceridaemia, visceral adiposity and extramyocellular lipid deposition were negatively associated with adipose tissue Fndc5 mRNA and circulating irisin. Moreover, mimicking diabetic status in vitro by treating muscle cells with palmitate and glucose lowered Fndc5 mRNA. Neither exercise training nor an acute exercise bout modulated circulating irisin or muscle Fndc5 expression. However, the associations between intensity of habitual physical activity, muscle volume, strength, contractility and circulating irisin provide a link between irisin and positive outcomes of increased physical activity.

Sport-Specific Balance

This review includes the latest findings based on experimental studies addressing sport-specific balance, an area of research that has grown dramatically in recent years. The main objectives of this work were to investigate the postural sway response to different forms of exercise under laboratory and sport-specific conditions, to examine how this effect can vary with expertise, and to provide examples of the association of impaired balance with sport performance and/or increasing risk of injury. In doing so, sports where body balance is one of the limiting factors of performance were analyzed. While there are no significant differences in postural stability between athletes of different specializations and physically active individuals during standing in a standard upright position (e.g., bipedal stance), they have a better ability to maintain balance in specific conditions (e.g., while standing on a narrow area of support). Differences in magnitude of balance impairment after specific exercises (rebound jumps, repeated rotations, etc.) and mainly in speed of its readjustment to baseline are also observed. Besides some evidence on an association of greater postural sway with the increasing risk of injuries, there are many myths related to the negative influence of impaired balance on sport performance. Though this may be true for shooting or archery, findings have shown that in many other sports, highly skilled athletes are able to perform successfully in spite of increased postural sway. These findings may contribute to better understanding of the postural control system under various performance requirements. It may provide useful knowledge for designing training programs for specific sports.

Interrelation of 31P-MRS metabolism measurements in resting and exercised quadriceps muscle of overweight-to-obese sedentary individuals

Phosphorus magnetic resonance spectroscopy (31P‐MRS) enables the non‐invasive evaluation of muscle metabolism. Resting Pi‐to‐ATP flux can be assessed through magnetization transfer (MT) techniques, and maximal oxidative flux (Qmax) can be calculated by monitoring of phosphocreatine (PCr) recovery after exercise. In this study, the muscle metabolism parameters of 13 overweight‐to‐obese sedentary individuals were measured with both MT and dynamic PCr recovery measurements, and the interrelation between these measurements was investigated. In the dynamic experiments, knee extensions were performed at a workload of 30% of maximal voluntary capacity, and the consecutive PCr recovery was measured in a quadriceps muscle with a time resolution of 2 s with non‐localized 31P‐MRS at 3 T. Resting skeletal muscle metabolism was assessed through MT measurements of the same muscle group at 7 T. Significant linear correlations between the Qmax and the MT parameters kATP (r = 0.77, P = 0.002) and FATP (r = 0.62, P = 0.023) were found in the study population. This would imply that the MT technique can possibly be used as an alternative method to assess muscle metabolism when necessary (e.g. in individuals after stroke or in uncooperative patients). Copyright

Physiological Mechanisms of Post-Exercise Balance Impairment

This review focuses on investigations into postural sway response to different forms of exercise, and particularly those dealing with physiological mechanisms of post-exercise balance impairment. The findings of relevant studies combined with our research results show that postural sway response to exercise depends on its type, intensity, duration and intensity of proprioceptive stimulation. Differences in postural sway were also observed after exercise with different forms of muscle contraction and those with different activation of muscle fibres. In general, fatigue is associated with post-exercise balance impairment. Such an effect is usually a consequence of prolonged exercise. However, findings proved that after short-term intensive exercises, hyperventilation, rather than fatigue, is responsible for increased postural sway. Significant differences in balance impairment were also found after exercises that induced the same ventilation but with a different intensity of muscle contractions eliciting a different level of proprioceptive stimulation, such as calf rises versus jumps and cycling versus running. Thus, in addition to fatigue and hyperventilation, impairment of somatosensory inputs also very likely plays a role in increased post-exercise postural sway. Based on this literature review, possible physiological mechanisms of post-exercise balance impairment identified so far may be fatigue, hyperventilation, deterioration of functions of mechanoreceptors, proprioceptors, vestibular apparatus and visual cues, muscle damage, dehydration, hyperthermia and dizziness. These findings can be explored in a more practical setting in the field of sport, clinical medicine and rehabilitation.

Power Outputs in the Concentric Phase of Resistance Exercises Performed in the Interval Mode on Stable and Unstable Surfaces

Abstract Zemková, E, Jeleň, M, Kováčiková, Z, Ollé, Z, Vilman, T, and Hamar, D. Power outputs in the concentric phase of resistance exercises performed in the interval mode on stable and unstable surfaces. J Strength Cond Res 26(12): 3230–3236, 2012—The study compares power outputs in the concentric phase of chest presses and squats performed in the interval mode on stable and unstable surface, respectively. A group of 16 physical education students performed randomly on different days 6 sets of 8 repetitions of (a) chest presses on the bench and Swiss ball, respectively, and (b) squats on stable support base and Bosu ball, respectively, with 2 minutes of rest period between sets. The exercises were performed with previously established 70% of 1 repetition maximum under stable conditions. A PC-based system FiTRO Dyne Premium was used to monitor force and velocity and to calculate power. The results showed significantly lower power outputs when resistance exercises were performed on an unstable than a stable support base. In the initial set, mean power in concentric phase of lifting decreased more profoundly under unstable than under stable conditions during both chest presses (13.2 and 7.7%, respectively) and squats (10.3 and 7.2%, respectively). In the final set, the reduction rates of mean power in the concentric phase of chest presses were significantly (p < 0.05) greater on the Swiss ball than on the bench (19.9 and 11.8%, respectively). On the other hand, there were no significant differences in decline of mean power in the concentric phase of squats on the Bosu ball and on stable support base (11.4 and 9.6%, respectively). It may be concluded that power outputs during resistance exercises is more profoundly compromised under unstable than under stable conditions, and this effect is more evident for barbell chest presses on the Swiss ball than for barbell squats on the Bosu ball. These findings have to be taken into account when instability resistance exercises are implemented into the training program, namely, for sports that require production of maximal force in short time.

Relationship of body mass status with running and jumping performances in young basketball players.

PURPOSE the main purpose of this study was to examine the relationship of body mass (BM) status with running and jumping performances in young male basketball players. METHODS basketball players (n=72, age 12.9±2.8 yrs), who were grouped into U-12 (9-12 yrs), U-15 (12-15 yrs) and U-18 (15-18 yrs), performed a battery of anthropometric, running and jumping tests. We examined differences among age groups, and between normal weight and overweight players. RESULTS the results indicated significant and large differences among age groups in BM, height, body mass index (BMI), fat mass (FM), fat-free mass, speed, endurance, standing long jump, countermovement jump (CMJ), mean power in 30 s jumping test (Pmean) (p<0.001, η(2)≥0.23) with older players presenting higher values. Within each age group, overweight players had higher BM, BMI, body fat percentage and FM (p<0.05) than their normal weight counterparts. Overweight players had worst performance in running (sprint and endurance) and jumping (CMJ and Pmean) in U-12, and worst endurance in U-18 (p<0.05, |d|≥0.82) than normal-weight players, whereas there was no difference in U-15. CONCLUSIONS it was concluded that the relationship of BMI with running and jumping performances varied according to age. Based on these findings, trainers and coaches should focus on special intervention exercise and nutrition programs targeting optimal body mass especially in young basketball players, where the excess of body mass seemed to have the most detrimental effect on running and jumping performances.

Concurrent validity of clinical tests for measuring hamstring flexibility in school age children.

The objectives were 1) to evaluate the hamstring muscle flexibility in children and adolescents; 2) to examine the relative contribution of the spinal curvatures, pelvic tilt and hamstring flexibility on the sit-and-reach (SR) score; and 3) to determine the validity of the sit-and-reach test through both active and passive hip flexion tests. 118 children and adolescents (aged 7-18 years; 60 males and 58 females) were tested for sit-and-reach (SR), passive straight leg raise (PSLR) and active straight leg raise (ASLR). The spinal curvatures and pelvic tilt were assessed during the SR test by means of the Spinal Mouse system. Females showed a statistically greater anterior pelvic tilt, distance reached in the SR test and hip flexion in both PSLR and ASLR tests than males. The pelvic tilt independently explained more than 60% of the variance (distance reached in the SR test) and in conjunction with lumbar flexion explained more than 80% of the variance. In conclusion, the pelvic tilt is the main determinant of SR test in school age children. The SR test can be considered an appropriate and valid test for evaluating pelvic tilt and lumbar flexion in school age children, but not to measure hamstring flexibility.

Weight Lifted and Countermovement Potentiation of Power in Concentric Phase of Unstable and Traditional Resistance Exercises

The study evaluates the effect of weight lifted on power in the concentric phase of resistance exercises on stable and unstable surfaces. A group of 19 fit men performed randomly on different days 3 reps of (a) barbell chest presses on the bench and Swiss ball, and (b) barbell squats on stable base and BOSU ball. Exercises were performed without and with countermovement (CM) using maximal effort in concentric phase. Initial weight of 20 kg was increased by 10 kg or 5 kg (at higher loads) up to at least 85% of previously established 1RM under stable conditions. Results showed no significant differences in mean power in the concentric phase of stable and unstable CM chest presses at lower weights lifted (from 20 to 50 kg). However, its values were significantly higher during chest presses on the bench than on Swiss ball while lifting higher weights (from 60 to 90 kg). Similarly, mean power in the concentric phase of squats was significantly higher on stable base than on BOSU ball at higher weights lifted (from 60 to 90 kg). Though a set of data showed significant differences, the effect sizes≤0.7 suggest no practically meaningful differences. It may be concluded that unstable base compromises the power in the concentric phase of resistance exercises, however, only at higher weights lifted.

Enhancement of Peak and Mean Power in Concentric Phase of Resistance Exercises

Abstract Zemková, E, Jeleň, MN, Kováčiková, ZC, Ollé, G, Vilman, TS, and Hamar, DS. Enhancement of peak and mean power in concentric phase of resistance exercises. J Strength Cond Res 28(10): 2919–2926, 2014—The study compares the differences in peak and mean power of concentric-only and countermovement resistance exercises (&Dgr;P) with different weights. A group of 27 fit men randomly performed 3 repetitions of either barbell bench presses or barbell squats on different days. The initial weight of 20 kg was increased by 10 or 5 kg (at higher loads) up to at least 85% of a previously established 1 repetition maximum (1RM). A computer-based system FiTRO Dyne Premium was used to monitor force and velocity and to calculate power. The peak values and mean values of power during the entire concentric phase of lifting and during the acceleration phase were analyzed. Results showed that maximal &Dgr;P calculated from the peak and mean values in the acceleration phase of bench presses was achieved at lower weights (118.4 ± 19.0 W at 47% of 1RM and 116.2 ± 15.3 W at 48% of 1RM, respectively) than the one calculated from mean values in the entire concentric phase of lifting (114.8 ± 14.8 W at 57% 1RM). Likewise, maximal &Dgr;P calculated from the peak and mean values in the acceleration phase of squats was achieved at lower weights (127.7 ± 20.4 W at 67% of 1RM and 124.3 ± 22.1 W at 69% of 1RM, respectively) than the one calculated from the mean values in the entire concentric phase of lifting (125.0 ± 19.2 W at 77% of 1RM). This fact has to be taken into account when training efficiency is evaluated, namely, in sports requiring the production of maximal force in a short time.

Load release balance test under unstable conditions effectively discriminates between physically active and sedentary young adults

This study investigates test-retest reliability and diagnostic accuracy of the load release balance test under four varied conditions. Young, early and late middle-aged physically active and sedentary subjects performed the test over 2 testing sessions spaced 1week apart while standing on either (1) a stable or (2) an unstable surface with (3) eyes open (EO) and (4) eyes closed (EC), respectively. Results identified that test-retest reliability of parameters of the load release balance test was good to excellent, with high values of ICC (0.78-0.92) and low SEM (7.1%-10.7%). The peak and the time to peak posterior center of pressure (CoP) displacement were significantly lower in physically active as compared to sedentary young adults (21.6% and 21.0%) and early middle-aged adults (22.0% and 20.9%) while standing on a foam surface with EO, and in late middle-aged adults on both unstable (25.6% and 24.5%) and stable support surfaces with EO (20.4% and 20.0%). The area under the ROC curve >0.80 for these variables indicates good discriminatory accuracy. Thus, these variables of the load release balance test measured under unstable conditions have the ability to differentiate between groups of physically active and sedentary adults as early as from 19years of age.