The effect of high volume stretch-shortening cycle exercise on muscle and connective tissue damage

Abstract

Intense or rather prolonged exercises, especially stretch-shortening cycle type (various jumps, throws), induce muscle (Allen, 2008) and connective tissue damage (Buchanan & Marsh, 2002). Muscle damage is characterized by prolonged decrease in muscle contraction strength, swelling, stiffness, soreness and an increase in the level of muscle creatine kinase (CK) activity in the blood (Byrne et al., 2004; Chen et al., 2013; Nosaka & Clarkson, 1996; Skurvydas et al., 2011). These symptoms are widely accepted as indirect indicators of muscle damage (Clarkson & Hubal, 2002; Warren et al., 1999). The ultrastructural changes of myofibril sarcomere, desmin and other cytoskeleton proteins, ultrastructural changes in sarcolemma are directly visible by an electron microscope (Féasson et al., 2002; Hortobágyi et al., 1998; Lauritzen et al., 2009). The damage to the connective tissue is indicated by a change in the distorted tendon appearance, an increase in the number of immature cells and apoptotic cells, disorganized collagen bundles, increased proteoglycan content and neovascularization in the tendons, changes in the extracellular matrix. Adaptation of the human motor system to muscle damage is quite well researched, although adaptation mechanisms are still not clear. The effects of physical exercises on the structure and metabolism of connective tissue have been significantly less studied (Tardioli et al., 2012), although changes in connective tissue are documented in a rather detailed way histologically (Maffulli et al., 2000), biochemically (Waśkiewicz et al., 2012) and clinical practice (Grigg et al., 2009). Physical exercises can promote the development of the structural and functional properties of the tendons (Nelly Andarawis-Puri et al., 2015). The process of tendon reconstruction involves collagen synthesis and degradation, which begin immediately after physical exercise (Magnusson et al., 2010). Studies using animal models have shown that physical exercise leads to an increase in the number of cells in the tendons, in particular of stem origin, and in the activation of collagen synthesis (Zhang et al., 2010). Studies have also shown that changes in the tendon depend on the recovery period between physical exercises, and the absence of a recovery period stimulates tendon degeneration instead of adaptation (Ristolainen et al., 2014). Healthy tendons are less affected by physical activity, whereas damaged tendons become thicker (Fredberg, Bolvign, 2002; O’Connor et al., 2004). Stretch-shortening cycle exercises are widely used to improve the muscular strenght of athletes and healthy non-professional subjects (Markovic, 2007). These physical exercises are recommended to be used carefully because a high numbers of jumps / throws can lead to chronic fatigue and reduce the effectiveness of exercise (Seynnes et al., 2013). Extremely large eccentric concentric loads are believed to not only cause muscle damage but also adversely affect the structural integrity of the tendons and ligaments. In the first study, we investigated the impact of particularly high volume single bout exercise on the adaptation of the motor system, as the intensification of the training process raises the need to know the limits of safe physical activity. It is known that the cyclists’ quadriceps muscles do not perform eccentric work during the specific exercise in the sport (avoids damage), but long-distance runners’ thigh, calf and foot muscles often experience muscle damage during training and competition (Kuipers, 1989; Warhol et al., 1985). Fredberg et al. (2007) have hypothesized that tendon changes detected by ultrasound examination appear before they occur clinically and are therefore very important for the examination of the long-term adaptation of athletes (Couppe et al., 2008; Fahlström & Alfredson, 2010). Depending on the specialization of the sport, the sensitivity of not only the muscle, but also of the connective tissue damage may vary. So, in the second study, we investigated how different sports specializations affect the long-term adaptation of muscles and connective tissue to specific physical activity, and how the indices of muscle and connective tissue damage vary for athletes specializing in different sports while they perform single bout unconventional eccentric exercise of 100 jumps. Recent studies have shown that the motor system is sensitive to the strategy of increasing physical load (Kamandulis et al., 2011, 2012). Muscle damage can be avoided by consistently involving physical exercises and gradually increasing the volume and intensity of exercise as well as the range of motion (Kamandulis et al., 2011). The adaptation of the motor system is higher when we apply the strategy of rapid instead of gradual increase in physical load (Chen et al., 2013). Exercise frequency is another factor that should be considered when planning the training process. Regarding sports activities, maximal intensity eccentric-concentric exercises are performed no more than 2–3 times a week, with sufficient time for the recovery of the body. Sometimes coaches use high intensity exercise more often than three times a week, but for a relatively short time (a microcycle of 5–9 days). In this way, great fatigue and damage is caused deliberately in the hope of higher supercompensation during recovery. However, there is a lack of data in the literature on the effects of frequent jump training loads on changes in muscles and connective tissue. Chen and Hsieh (2001) found that daily, repetitive, maximal eccentric exercise of constant volume did not increase muscle damage and inflammation during the seven days of training. However, the peculiarities of adaptation of muscles and tendons when using the strategy of rapid increase in workload with a short period of time between exercises are not known. Aiming at establishing the impact of such strategy on the motor system, we performed a repeated 9-day increasing physical workload involving jumps. Research aim To establish the effect of high volume and frequent stretch-shortening cycle exercise as well as different sports specializations on muscle and connective tissue damage. Research objectives 1. To establish the effect of a high volume single bout stretch-shortening cycle exercise on muscle and connective tissue damage. 2. To establish the effect of a high volume single bout stretch-shortening cycle exercise on muscle and connective tissue damage for athletes of different specializations. 3. To establish the effect of frequenly performed gradually increasing stretch-shortening cycle exercise on muscle and connective tissue damage. Theoretical and practical significance So far, it has not been known whether such high volume eccentric concentric exercise is safe for muscles and connective tissues. Thus, according to the data presented in the dissertation, it can be argued that high volume single bout eccentric concentric physical exercise (200 jumps) induces moderate muscle damage in physically active men, but minimally changes the morphological parameters of the tendons and is relatively safe for completely healthy tendons, however, it can cause muscle soreness when initial signs of connective tissue (tendons, ligaments) damage are present. Sports specialization has a small effect on muscle sensitivity for damage, i.e. long-term concentric exercise (cycling) can lead to increased muscle soreness and sarcolemmal damage as compared to long-term eccentric-concentric exercises (long run races), but the sensitivity of tendons to damage tends to vary slightly. However, we do not recommend performing high volume eccentric-concentric physical exercises every day: although muscle and connective tissue damage is not high, i.e. training is relatively safe, but such training method is not very effective. CONCLUSIONS 1. The large volume single-bout stretch-shortening cycle (200 jumps) exercise induces moderate muscle damage in physically active males, but makes little change to the morphological characteristics of the tendons. The stretch-shortening cycle exercise of this volume is relatively safe for completely healthy tendons, but can provoke muscle soreness when there are primary signs of connective tissue (tendons, ligaments) damage. 2. The large volume single-bout stretch-shortening cycle (100 jumps) physical exercise causes moderate muscle damage to endurance athletes. Eccentrically-concentrically trained long-distance runners are less susceptible to muscle soreness and sarcolemmal damage than concentrically trained cyclists, but the differences in the torque of muscle contraction force are not significant between these groups. The thickness of the proximal part of the patella and the cross-sectional area of the distal part of the Achilles tendon in runners increased after 24 hours after performing jumps from the platform, but other morphological indices of the tendons did not change, indirectly confirming that a single bout, even high-volume unusual eccentric-concentric physical load causes minimal damage to the connective tissue. 3. Frequently repeated stretch-shortening cycle exercises cause moderate muscle damage, which especially increases while increasing the range of motion, but the changes in the connective tissue damage during this exercise are relatively negligible. At the time of recovery after such exercise, the height of the jump increases, but the maximal voluntary contaction torque and electrostimulation evoked muscle contraction torque remain at the same level as before the exercise. High volume stretch-shortening cycle exercises are fairly safe to be performed every day, as the muscle and connective tissue damage is not high; however, this method of training is not very effective