Search results for "shortening"
showing 10 items of 79 documents
Effects of exhaustive stretch-shortening cycle exercise on muscle blood flow during exercise
2006
Aim: The influence of exhaustive stretch-shortening cycle exercise (SSC) on skeletal muscle blood flow (BF) during exercise is currently unknown. Methods: Quadriceps femoris (QF) BF was measured in eight healthy men using positron emission tomography before and 3 days after exhaustive SSC exercise. The SSC protocol consisted of maximal and submaximal drop jumps with one leg. Needle biopsies of the vastus lateralis muscles were taken immediately and 2 days after SSC for muscle endothelial nitric oxide synthase (eNOS) and interleukin-1-beta (IL-1β) mRNA level determinations. Results: All subjects reported subjective muscle soreness after SSC (P < 0.001), which was well in line with a decre…
The mechanical efficiency of locomotion in men and women with special emphasis on stretch-shortening cycle exercises.
1986
The mechanical efficiency of the leg extensor musculature of men and women was examined with a special "sledge ergometer". The subjects (ten males and ten females) performed pure positive work, pure negative work and a combination of negative and positive work (stretch-shortening cycle). The mechanical efficiency of pure positive work was on average 19.8 +/- 1.2% for female subjects and 17.4 +/- 1.2% for male subjects (t = 4.12, P less than 0.001), although the work intensity was equal in both groups. The mechanical efficiency of pure negative work was slightly lower in women than in men (59.3 +/- 14.4% vs 75.6 +/- 29.3%). The mechanical efficiency of positive work (eta +) in a stretch-shor…
Differences in mechanical efficiency between power- and endurance-trained athletes while jumping
1995
Mechanical efficiency (ME) of jumping exercises was compared between power-trained (n = 11) and endurance-trained athletes (n = 10) using both a biomechanical and a physiological approach. In drop jumps and in stretch-shortening cycle exercise on a special sledge (sledge jumps), the subjects performed 60 muscle actions from a dropping height of optimum minus 40 cm (O − 40), as well as from dropping heights of optimum (O) and optimum plus 40 cm (O + 40). Thus, they were tested in six different tests which lasted for a total of 3 min for each. The mean ME values in the drop jumps from the lowest dropping height upwards were as follows: 23.8 (SD 5.3)%, 35.5 (SD 10.8)% and 39.2 (SD 6.6)% for th…
Interaction between pre-landing activities and stiffness regulation of the knee joint musculoskeletal system in the drop jump: implications to perfor…
2002
The purpose of the present study was to investigate the interaction between the pre-landing activities and the stiffness regulation of the knee joint musculoskeletal system and the takeoff speed during a drop jump (DJ). Nine healthy male subjects performed a DJ test from the height of 50 cm. The surface electromyographic (EMG) activity of the vastus lateralis (VL) muscle was recorded to evaluate both the pre-landing and post-landing muscle activation levels. Simultaneous recording of the jumping motion and ground reaction force was performed by a high-speed video camera (100 frames x s(-1)), and a force platform was employed to allow joint moment analysis. Joint stiffness was calculated by …
Conditioning hops increase triceps surae muscle force and Achilles tendon strain energy in the stretch-shortening cycle
2018
Postactivation potentiation can improve athletic performance, but the underlying mechanisms are poorly understood. This study investigated the effect of conditioning hops on triceps surae muscle force and tendon strain and its contribution to potentiated stretch-shortening cycle (SSC) performance. Thirty-two subjects participated in two experiments. In both experiments, subjects performed three drop jumps (DJs) after prior conditioning with 10 maximal hops, three unconditioned DJs served as control. Ground reaction forces, kinematics, and triceps surae electromyographic activity were recorded. Ultrasound imaging was used to determine fascicle lengths (FASC) of the gastrocnemius (GM) and sol…
Postactivation potentiation can counteract declines in force and power that occur after stretching.
2016
Stretching can decrease a muscle's maximal force, whereas short but intense muscle contractions can increase it. We hypothesized that when combined, postactivation potentiation induced by reactive jumps would counteract stretch-induced decrements in drop jump (DJ) performance. Moreover, we measured changes in muscle twitch forces and ankle joint stiffness (KAnkle ) to examine underlying mechanisms. Twenty subjects completed three DJs and 10 electrically evoked muscle twitches of the triceps surae subsequent to four different conditioning activities and control. The conditioning activities were 10 hops, 20s of static stretching of the triceps surae muscle, 20s of stretching followed by 10 ho…
Intensity- and muscle-specific fascicle behavior during human drop jumps.
2006
The present study was designed to examine fascicle-tendon interaction in the synergistic medial gastrocnemius (MG) and soleus (Sol) muscles during drop jumps (DJ) performed from different drop heights (DH). Eight subjects performed unilateral DJ with maximal rebounds on a sledge apparatus from different DH. During the exercises, fascicle lengths (using ultrasonography) and electromyographic activities were recorded. The results showed that the fascicles of the MG and Sol muscles behaved differently during the contact phase, but the whole muscle-tendon unit and its tendinous tissue lengthened before shortening in both muscles. The Sol fascicles also lengthened before shortening during the g…
Mechanical efficiency of locomotion in females during different kinds of muscle action
1990
The mechanical efficiencies (ME) of pure positive and pure negative work as well as of stretch-shortening cycle (SSC) exercise were investigated with a special sledge apparatus. The subjects were 20 young females who performed six different types of submaximal exercise: two of pure concentric exercise (positive work), two of pure eccentric exercise (negative work) and two SSC exercises. The work intensities were determined individually, from the recordings of distance obtained during a single maximal concentric exercise. Each exercise involved 60 muscle actions lasting a total of 3 min per testing condition. The MEs of pure positive work with intensities of 30% and 60% maximum (C30 and C60 …
Muscle damage induced by stretch-shortening cycle exercise
1998
Strenuous stretch-shortening cycle exercise was used as a model to study the leakage of proteins from skeletal muscle.The analysis included serum levels of creatine kinase (S-CK), myoglobin (S-Mb), and carbonic anhydrase (S-CA III). Blood samples from power- (N=11) and endurance-trained (N=10) athletes were collected before, 0, and 2 h after the exercise, which consisted of a total of 400 jumps.The levels of all determined myocellular proteins increased immediately after the exercise (P0.05-0.001) among both subject groups. In the endurance group, the protein levels increased (P0.05-0.001) further during the following 2 h after the exercise, and the ratio of S-CA III and S-Mb decreased (P0.…
Combined effect of elastic energy and myoelectrical potentiation during stretch-shortening cycle exercise.
1982
In addition to the utilization of muscle's elastic energy enhancement of performance in exercise involving stretch-shortening cycle might be also due to simultaneous increase of myoelectrical activity. This hypothesis was tested by examining three athletes during jumping exercise on force-platform. Vertical jumps were performed with and without preliminary counter-movement, and the jumps were called counter-movement jump (CMJ) and squatting jump (SJ), respectively. In both conditions several jumps were performed also with extra loads on the shoulders (15–220% of b. wt.). Additional droppingjumps (DJ) were executed from different heights (20–100 cm). During jumping exercise myoelectrical act…