Nejc Sarabon

Does pre‐exercise static stretching inhibit maximal muscular performance? A meta‐analytical review

We applied a meta‐analytical approach to derive a robust estimate of the acute effects of pre‐exercise static stretching (SS) on strength, power, and explosive muscular performance. A computerized search of articles published between 1966 and December 2010 was performed using PubMed, SCOPUS, and Web of Science databases. A total of 104 studies yielding 61 data points for strength, 12 data points for power, and 57 data points for explosive performance met our inclusion criteria. The pooled estimate of the acute effects of SS on strength, power, and explosive performance, expressed in standardized units as well as in percentages, were −0.10 [95% confidence interval (CI): −0.15 to −0.04], −0.04 (95% CI: −0.16 to 0.08), and −0.03 (95% CI: −0.07 to 0.01), or −5.4% (95% CI: −6.6% to −4.2%), −1.9% (95% CI: −4.0% to 0.2%), and −2.0% (95% CI: −2.8% to −1.3%). These effects were not related to subjects age, gender, or fitness level; however, they were more pronounced in isometric vs dynamic tests, and were related to the total duration of stretch, with the smallest negative acute effects being observed with stretch duration of ≤45 s. We conclude that the usage of SS as the sole activity during warm‐up routine should generally be avoided.

Lifelong Physical Exercise Delays Age-Associated Skeletal Muscle Decline

Aging is usually accompanied by a significant reduction in muscle mass and force. To determine the relative contribution of inactivity and aging per se to this decay, we compared muscle function and structure in (a) male participants belonging to a group of well-trained seniors (average of 70 years) who exercised regularly in their previous 30 years and (b) age-matched healthy sedentary seniors with (c) active young men (average of 27 years). The results collected show that relative to their sedentary cohorts, muscle from senior sportsmen have: (a) greater maximal isometric force and function, (b) better preserved fiber morphology and ultrastructure of intracellular organelles involved in Ca(2+) handling and ATP production, (c) preserved muscle fibers size resulting from fiber rescue by reinnervation, and (d) lowered expression of genes related to autophagy and reactive oxygen species detoxification. All together, our results indicate that: (a) skeletal muscle of senior sportsmen is actually more similar to that of adults than to that of age-matched sedentaries and (b) signaling pathways controlling muscle mass and metabolism are differently modulated in senior sportsmen to guarantee maintenance of skeletal muscle structure, function, bioenergetic characteristics, and phenotype. Thus, regular physical activity is a good strategy to attenuate age-related general decay of muscle structure and function (ClinicalTrials.gov: NCT01679977).

Long-Term High-Level Exercise Promotes Muscle Reinnervation With Age

The histologic features of aging muscle suggest that denervation contributes to atrophy, that immobility accelerates the process, and that routine exercise may protect against loss of motor units and muscle tissue. Here, we compared muscle biopsies from sedentary and physically active seniors and found that seniors with a long history of high-level recreational activity up to the time of muscle biopsy had 1) lower loss of muscle strength versus young men (32% loss in physically active vs 51% loss in sedentary seniors); 2) fewer small angulated (denervated) myofibers; 3) a higher percentage of fiber-type groups (reinnervated muscle fibers) that were almost exclusive of the slow type; and 4) sparse normal-size muscle fibers coexpressing fast and slow myosin heavy chains, which is not compatible with exercise-driven muscle-type transformation. The biopsies from the old physically active seniors varied from sparse fiber-type groupings to almost fully transformed muscle, suggesting that coexpressing fibers appear to fill gaps. Altogether, the data show that long-term physical activity promotes reinnervation of muscle fibers and suggest that decades of high-level exercise allow the body to adapt to age-related denervation by saving otherwise lost muscle fibers through selective recruitment to slow motor units. These effects on size and structure of myofibers may delay functional decline in late aging.

Electrical Stimulation Counteracts Muscle Decline in Seniors

The loss in muscle mass coupled with a decrease in specific force and shift in fiber composition are hallmarks of aging. Training and regular exercise attenuate the signs of sarcopenia. However, pathologic conditions limit the ability to perform physical exercise. We addressed whether electrical stimulation (ES) is an alternative intervention to improve muscle recovery and defined the molecular mechanism associated with improvement in muscle structure and function. We analyzed, at functional, structural, and molecular level, the effects of ES training on healthy seniors with normal life style, without routine sport activity. ES was able to improve muscle torque and functional performances of seniors and increased the size of fast muscle fibers. At molecular level, ES induced up-regulation of IGF-1 and modulation of MuRF-1, a muscle-specific atrophy-related gene. ES also induced up-regulation of relevant markers of differentiating satellite cells and of extracellular matrix remodeling, which might guarantee shape and mechanical forces of trained skeletal muscle as well as maintenance of satellite cell function, reducing fibrosis. Our data provide evidence that ES is a safe method to counteract muscle decline associated with aging.

Aerodynamic drag is not the major determinant of performance during giant slalom skiing at the elite level.

This investigation was designed to (a) develop an individualized mechanical model for measuring aerodynamic drag (Fd) while ski racing through multiple gates, (b) estimate energy dissipation (Ed) caused by Fd and compare this to the total energy loss (Et), and (c) investigate the relative contribution of Ed/Et to performance during giant slalom skiing (GS). Nine elite skiers were monitored in different positions and with different wind velocities in a wind tunnel, as well as during GS and straight downhill skiing employing a Global Navigation Satellite System. On the basis of the wind tunnel measurements, a linear regression model of drag coefficient multiplied by cross‐sectional area as a function of shoulder height was established for each skier (r > 0.94, all P < 0.001). Skiing velocity, Fd, Et, and Ed per GS turn were 15–21 m/s, 20–60 N, −11 to −5 kJ, and −2.3 to −0.5 kJ, respectively. Ed/Et ranged from ∼5% to 28% and the relationship between Et/vin and Ed was r = −0.12 (all NS). In conclusion, (a) Fd during alpine skiing was calculated by mechanical modeling, (b) Ed made a relatively small contribution to Et, and (c) higher relative Ed was correlated to better performance in elite GS skiers, suggesting that reducing ski–snow friction can improve this performance.

Effects of whole‐body cryotherapy on recovery after hamstring damaging exercise: A crossover study

The purpose of this study was to examine the effects of whole‐body cryotherapy (WBC) on biochemical, pain, and performance parameters during the 5‐day recovery period after damaging exercise for hamstrings. Participants completed a bout of damaging exercise for the hamstring muscles on two separate occasions (control and experimental condition) separated by 10 weeks. During the control condition, subjects received no treatment after the damaging exercise. The experimental condition consisted of WBC everyday during the recovery period. WBC included single 3‐min daily exposures to low temperatures (−140 to −195 °C) in the cryo‐cabin. During the recovery period, subjects were tested for biochemical markers, perceived pain sensation, and physical performance (squat jump, counter movement jump, maximal isometric torque production, and maximally explosive isometric torque production). Majority of the observed variables showed statistically significant time effects (P < 0.05) in control group, which indicates the presence of muscle damage. Significant interaction between the control and WBC condition was evident for the rate of torque development (P < 0.05). Pain measures substantially differed between the WBC and the control condition after the exercise. Results of this study are not completely supportive of the use of WBC for recovery enhancement after strenuous training.

Atrophy/hypertrophy cell signaling in muscles of young athletes trained with vibrational-proprioceptive stimulation

Abstract Objective: To compare the effects of isokinetic (ISO-K) and vibrational-proprioceptive (VIB) trainings on muscle mass and strength. Methods: In 29 ISO-K- or VIB-trained young athletes we evaluated: force, muscle fiber morphometry, and gene expression of muscle atrophy/hypertrophy cell signaling. Results: VIB training increased the maximal isometric unilateral leg extension force by 48·1%. ISO-K training improved the force by 24·8%. Both improvements were statistically significant (P0·01). The more functional effectiveness of the VIB training in comparison with the ISO-K training was shown by the statistical significance changes only in VIB group in: rate of force development in time segment 0-50 ms (P<0·001), squat jump (P<0·05) and 30-m acceleration running test (P<0·05). VIB training induced a highly significant increase of mean diameter of fast fiber (+9%, P<0·001), but not of slow muscle fibers (−3%, not significant). No neural cell adhesion molecule-positive (N-CAM+) and embryonic myosin heavy chain-positive (MHC-emb+) myofibers were detected. VIB induced a significant twofold increase (P<0·05) of the skeletal muscle isoform insulin-like growth factor-1 (IGF-1) Ec mRNA. Atrogin-1 and muscle ring finger-1 (MuRF-1) did not change, but myostatin was strongly downregulated after VIB training (P<0·001). Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) expression increased in post-training groups, but only in VIB reached statistical significance (+228%, P<0·05). Discussion: We demonstrated that both trainings are effective and do not induce muscle damage. Only VIB-trained group showed statistical significance increase of hypertrophy cell signaling pathways (IGF-1Ec and PGC-1α upregulation, and myostatin downregulation) leading to hypertrophy of fast twitch muscle fibers.

Effects of vertical center of mass redistribution on body sway parameters during quiet standing

Body sway is usually described by center of foot pressure (COP)-derived parameters. Their sensitivity to vertical center of mass (COM) redistribution below its natural position has not yet been examined during quiet stance tasks. We examined the effects of both lowering and raising the COM on the following body sway parameters: cumulative, medial-lateral and anterior-posterior COP average velocity, amplitude and frequency. For this purpose, 13 healthy male subjects performed a quiet stance balance task with feet positioned in parallel stance (PS) at hip width apart and with hands holding a stick across the rear part of the shoulders. Each subject carried out five different modifications of the PS task in a randomized order: no additional load, an additional load of 10 kg and 30 kg suspended from the waist at mid-lower leg height, and an additional load of 10 kg and 30 kg across the rear of the shoulders. The studied body sway parameters proved to be sensitive to these manipulations. Specifically, lowering and raising the COM was mirrored in a systematic decrease/increase of the velocity, amplitude, and frequency parameters, indicating a larger effect in the anterior-posterior direction. These results suggest that the elevation of the body COM from a lower to a higher position systematically decreases the postural control during quiet standing, and consequently, increases the intensity of the balancing task. Thus, this type of physical manipulation could provide the basis for a simple progression in functional resistance training for persons with compromised balance.

Physical exercise in Aging: Nine weeks of leg press or electrical stimulation training in 70 years old sedentary elderly people

Sarcopenia is the age-related loss of muscle mass and function, reducing force generation and mobility in the elderlies. Contributing factors include a severe decrease in both myofiber size and number as well as a decrease in the number of motor neurons innervating muscle fibers (mainly of fast type) which is sometimes accompanied by reinnervation of surviving slow type motor neurons (motor unit remodeling). Reduced mobility and functional limitations characterizing aging can promote a more sedentary lifestyle for older individuals, leading to a vicious circle further worsening muscle performance and the patients’ quality of life, predisposing them to an increased risk of disability, and mortality. Several longitudinal studies have shown that regular exercise may extend life expectancy and reduce morbidity in aging people. Based on these findings, the Interreg IVa project aimed to recruit sedentary seniors with a normal life style and to train them for 9 weeks with either leg press (LP) exercise or electrical stimulation (ES). Before and at the end of both training periods, all the subjects were submitted to mobility functional tests and muscle biopsies from the Vastus Lateralis muscles of both legs. No signs of muscle damage and/or of inflammation were observed in muscle biopsies after the training. Functional tests showed that both LP and ES induced improvements of force and mobility of the trained subjects. Morphometrical and immunofluorescent analyses performed on muscle biopsies showed that ES significantly increased the size of fast type muscle fibers (p<0.001), together with a significant increase in the number of Pax7 and NCAM positive satellite cells (p<0.005). A significant decrease of slow type fiber diameter was observed in both ES and LP trained subjects (p<0.001). Altogether these results demonstrate the effectiveness of physical exercise either voluntary (LP) or passive (ES) to improve the functional performances of aging muscles. Here ES is demonstrated to be a safe home-based method to counteract fast type fiber atrophy, typically associated with aging skeletal muscle.

Validity and reliability of different kinematics methods used for bike fitting

Abstract The most common bike fitting method to set the seat height is based on the knee angle when the pedal is in its lowest position, i.e. bottom dead centre (BDC). However, there is no consensus on what method should be used to measure the knee angle. Therefore, the first aim of this study was to compare three dynamic methods to each other and against a static method. The second aim was to test the intra-session reliability of the knee angle at BDC measured by dynamic methods. Eleven cyclists performed five 3-min cycling trials; three at different seat heights (25°, 30° and 35° knee angle at BDC according to static measure) and two at preferred seat height. Thirteen infrared cameras (3D), a high-speed camera (2D), and an electrogoniometer were used to measure the knee angle during pedalling, when the pedal was at the BDC. Compared to 3D kinematics, all other methods statistically significantly underestimated the knee angle (P = 0.00; η2 = 0.73). All three dynamic methods have been found to be substantially different compared to the static measure (effect sizes between 0.4 and 0.6). All dynamic methods achieved good intra-session reliability. 2D kinematics is a valid tool for knee angle assessment during bike fitting. However, for higher precision, one should use correction factor by adding 2.2° to the measured value.