Priit Kaasik

Review on aging, unloading and reloading: Changes in skeletal muscle quantity and quality

Aging and muscle unloading are associated with a decline in muscle mass, structure, force and changes in the mechanical properties of skeletal muscle. There is a perception that reloading restores muscle architecture and function but differences in the regeneration capacity of intra- and extra-cellular compartments, age dependent susceptibility to muscle damage, particularly in the contractile machinery, make it difficult to attribute the main role of the above mentioned components. This review briefly summarizes studies that examine aging skeletal muscle during unloading and reloading. The article highlights changes in muscle mass, structure, extra-cellular matrix (ECM) components, strength, locomotion, adaptability to exercise, peculiarities of protein metabolism, susceptibility to glucocorticoids and recovery of muscle from injury.

Dissociation between running economy and running performance in elite Kenyan distance runners

Abstract The purpose of this study was to investigate the relationship between running economy (RE) and performance in a homogenous group of competitive Kenyan distance runners. Maximal aerobic capacity (VO2max) (68.8 ± 3.8 ml∙kg−1∙min−1) was determined on a motorised treadmill in 32 Kenyan (25.3 ± 5.0 years; IAAF performance score: 993 ± 77 p) distance runners. Leg anthropometry was assessed and moment arm of the Achilles tendon determined. While Achilles moment arm was associated with better RE (r2 = 0.30, P = 0.003) and upper leg length, total leg length and total leg length to body height ratio were correlated with running performance (r = 0.42, P = 0.025; r = 0.40, P = 0.030 and r = 0.38, P = 0.043, respectively), RE and maximal time on treadmill (tmax) were not associated with running performance (r = −0.01, P = 0.965; r = 0.27; P = 0.189, respectively) in competitive Kenyan distance runners. The dissociation between RE and running performance in this homogenous group of runners would suggest that RE can be compensated by other factors to maintain high performance levels and is in line with the idea that RE is only one of many factors explaining elite running performance.

Muscle Protein Turnover in Endurance Training: a Review

There has been much debate about skeletal muscle capacity to adapt to long-lasting endurance exercise. Exercise in the aerobic zone of metabolism does not result in hypertrophy of skeletal muscle fibres but increases their oxidative capacity. The duration and intensity of an exercise session determines the time period of depressed muscle protein synthesis and increased degradation rate during the recovery period after exercise. Protein turnover characterizes the renewal processes of muscle proteins and the functional capacity of muscle. The turnover rate of myofibrillar proteins is slow in comparison with mitochondrial proteins and depends on the oxidative capacity of muscle fibres. The turnover rate of myofibrillar proteins in the same muscle is different and is also different within the myosin molecule between myosin heavy and light chain isoforms. The turnover rate of muscle proteins in endurance training shows the adaptation of skeletal muscle to long-lasting exercise via remodelling of muscle structures. Adaptational coordination between myofibrillar and mitochondrial compartments shows the physiological role and adaptational capacity of skeletal muscle to endurance training. It is challenging to use muscle protein turnover for the purposes of monitoring the training process of endurance athletes, optimizing training programs and preventing overtraining.

Ageing and dexamethasone associated sarcopenia: peculiarities of regeneration.

The purpose of this study was to assess the development of ageing- and glucocorticoid-related sarcopenia on the level of myofibrillar apparatus, paying attention to the synthesis (SR) and degradation rate (DR) of contractile proteins, muscle strength, and daily motor activity. We also wanted to test the effect of ageing and dexamethasone (Dex) excess on the regeneration peculiarities of skeletal muscle autografts. Four and 30-month-old male rats of the Wistar strain were used. Ageing associated sarcopenia was calculated from gastrocnemius muscle relative mass decrease (from 5.6 +/- 0.08 to 3.35 +/- 0.04; p < 0.001). The SR of MyHC in old rats was approximately 30% and actin approximately 23% lower than in young rats. Dex treatment decreased SR of two main contractile proteins significantly in both age groups (p < 0.001) and increased DR during ageing from 2.11 +/- 0.15 to 4.09 +/- 0.29%/day (p < 0.001). Hindlimb grip strength in young rats was 5.90 +/- 0.35 N/100 g bw and 2.64 +/- 0.2 N/100 g bw (p < 0.001) in old rats. Autografts of old rats have a higher content of adipose tissue 14.9 +/- 1.1% in comparison with young rats 6.8 +/- 0.51% (p < 0.001) and less muscle tissue 39.8 +/- 2.6% and 48.3 +/- 2.8%, respectively (p < 0.05). Both, ageing and dex-caused sarcopenic muscles have diminished capacity for regeneration.

The Exercise Myopathy

The modern training of athletes is based on the overload principle and negative feedback theory: the training stimulus must be strong enough to induce disturbance of homeostasis so that the body has to initiate reactions to adapt to the training stimulus. This means that overloading is a natural part of an athletes training process and provides stimuli for adaptation and supercompensation. Imbalance in the training load-recovery relationship is the primary factor contributing to overtraining syndrome. The reflection of overtraining syndrome on the ultrastructural level of skeletal muscle has revealed that the damaging effect depends on the muscle fiber type.Due to the destruction of myofibrils and atrophy of muscle fibers, exercise myopathy develops as a result of overtraining . The most sensitive to the long-lasting exhaustive endurance exercise are fast-twitch muscle fibers. The aim of the present study was to investigate the reflection of exercise myopathy on the ultrastructural level of fast-twitch muscle fibers.

Muscle weakness in the elderly: role of sarcopenia, dynapenia, and possibilities for rehabilitation

Aging is a multifactorial process leading to changes in skeletal muscle quantity and quality, which cause muscle weakness and disability in the aging population. This paper discusses the reasons for muscle weakness—and its biological and physiological mechanisms—in the elderly and describes the role of sarcopenia and dynapenia, and the possibilities to modify the age-associated decline in muscle function and decelerate the development of muscle weakness and disability. Resistance and endurance training are effective measures of exercise therapy in the elderly, which improve muscle metabolism and thereby muscle function and life quality.

Physiological role of myosin light and heavy chain isoforms in fast- and slow-twitch muscles: effect of exercise

The aims of the present study were to show the distribution of individual myosin light chain (MyLC) isoforms in fast-twitch (FT) and slowtwitch (ST) muscles and between FT muscles in order to find differences between MyLC isoforms in these muscles, to identify similarities with the distribution of myosin heavy chain (MyHC) isoforms and to investigate changes in these relations during adaptation to endurance and resistance training. Male Wistar strain rats were used in this study. One-dimensional electrophoresis was used for separation of MyHC and MyLC isoforms and two-dimensional electrophoresis was used for identification of MyLC different isoforms. A difference in the relative content of MyLC isoforms between FT muscles exists only in the case of MyLC 1slow and 2slow isoforms. Differences in the relative content of MyHC between FT muscles are considerably larger than differences in the MyLC isoforms. MyHC and MyLC isoforms both participate in the remodelling of contractile proteins during exercise training. In conclusion: The present study shows some discrepancy between the modulation of MyHC and MyLC isoforms in muscles with different oxidative potential during adaptation to endurance and resistance training. In ST muscles, there is full agreement between the increase in the relative content of MyHC IIa isoform and MyLC 2fast and 3fast isoforms during resistance training without significant changes during endurance training. The ratio of MyLC 3 and MyLC 2 isoforms increases during both types of exercise training, but it is two times higher during resistance training. (Biol.Sport 26:215-234, 2009)

Role of Exercise Therapy in Prevention of Decline in Aging Muscle Function: Glucocorticoid Myopathy and Unloading

Changes in skeletal muscle quantity and quality lead to disability in the aging population. Physiological changes in aging skeletal muscle are associated with a decline in mass, strength, and inability to maintain balance. Glucocorticoids, which are in wide exploitation in various clinical scenarios, lead to the loss of the myofibrillar apparatus, changes in the extracellular matrix, and a decrease in muscle strength and motor activity, particularly in the elderly. Exercise therapy has shown to be a useful tool for the prevention of different diseases, including glucocorticoid myopathy and muscle unloading in the elderly. The purpose of the paper is to discuss the possibilities of using exercise therapy in the prevention of glucocorticoid caused myopathy and unloading in the elderly and to describe relationships between the muscle contractile apparatus and the extracellular matrix in different types of aging muscles.

Myosin heavy chain pattern in the Akhal-Teke horses

This study investigates the myosin heavy chain (MyHC) isoform composition in the gluteus medius muscle of the Akhal-Teke horses using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). Fifteen horses aged between 1.5 and 23.5 years were used in this study and divided into three age groups: 1.5 to 4 (n = 6), 9 to 13 (n = 5) and 18.5 to 23.5 years (n = 4). The average content of the MyHC I isoform was 11.72 ± 1.07% (variation between individuals: 7.09% to 20.14%). The relative content of the MyHC IIa and IIx isoforms was subsequently 38.20 ± 1.46% (30.73% to 48.78%) and 50.07 ± 1.10% (43.8% to 56.78%) from the total MyHC. The MyHC pattern in the skeletal muscles of the Akhal-Teke horses shows that the muscles of these horses have a high capacity both for endurance and speed.

Different Methods Yielded Two-Fold Difference in Compliance with Physical Activity Guidelines on School Days.

Introduction The aim was to compare the average and the days method in exploring the compliance of children with physical activity guidelines and describe their physical activity patterns in different school day segments. Methods Physical activity was objectively measured in 472 children aged 6–13 for one school week. Children were compliant when fulfilling PA recommendations 1) on average over all measured days (average method) or 2) on at least four measured days (days method). To explore the difference in moderate to vigorous physical activity (MVPA) minutes between compliant and non-complaint children (using both the average and days method) in various day segments, linear mixed models was used. Results Compliance with physical activity guidelines was significantly higher with the average compared to the days method (51.7% and 23.7%, respectively). In segmented-day analysis, compliant children accrued more MVPA minutes in all day segments, especially during after-school. Gender differences appeared only during the in-school segments, where girls spent less time in MVPA (average method: -4.39 min, 95% CI = -5.36,-3.42, days method: -4.45 min, 95%CI = -5.46,-3.44). Older children accrued more MVPA minutes during physical education classes, but less during breaks, compared to younger children. Conclusions The used methods yielded remarkably different prevalence estimates for compliance to physical activity recommendations. To ensure comparability between studies, interventions and reports, there is a need for internationally agreed operationalization and assessment methods of physical activity guidelines. As non-compliant children had lower MVPA during all day segments, greater efforts should be made to provide physical activity opportunities both during and after school.