S. O.A. Koskinen

Effects of power training on muscle structure and neuromuscular performance

The present study examines changes in muscle structure and neuromuscular performance induced by 15 weeks of power training with explosive muscle actions. Twenty‐three subjects, including 10 controls, volunteered for the study. Muscle biopsies were obtained from the gastrocnemius muscle before and after the training period, while maximal voluntary isometric contractions (MVC) and drop jump tests were performed once every fifth week. No statistically significant improvements in MVC of the knee extensor (KE) and plantarflexor muscles were observed during the training period. However, the maximal rate of force development (RFD) of KE increased from 18 836±4282 to 25 443±8897 N (P<0.05) during the first 10 weeks of training. In addition, vertical jump height (vertical rise of the center of body mass) in the drop jump test increased significantly (P<0.01). Simultaneously, explosive force production of KE muscles measured as knee moment and power increased significantly; however, there was no significant change (P>0.05) in muscle activity (electromyography) of KE. The mean percentage for myosin heavy chain and titin isoforms, muscle fiber‐type distributions and areas were unchanged. The enhanced performance in jumping as a result of power training can be explained, in part, by some modification in the joint control strategy and/or increased RFD capabilities of the KE.

Increased mRNAs for procollagens and key regulating enzymes in rat skeletal muscle following downhill running.

Abstract The purpose of the study was to investigate pre-translational regulation of collagen expression after a single bout of exercise. We analysed steady-state messenger ribonucleic acid (mRNA) levels for collagen types I, III and IV, α- and β-subunits of prolyl 4-hydroxylase and lysyl oxidase (enzymes modifying procollagen chains), and enzyme activity of prolyl 4-hydroxylase from rat soleus muscle (MS) and the red parts of quadriceps femoris muscle (MQF) after 12 h and after 1, 2, 4, 7 and 14 days of downhill (–13.5°) treadmill running at a speed of 17 m·min–1 for 130 min. Histological and biochemical assays revealed exercise-induced muscle damage in MQF but not MS. Steady-state mRNA levels for the α- and β-subunits of prolyl 4-hydroxylase in MQF, lysyl oxidase in MS and MQF were increased 12 h after running, whereas prolyl 4-hydroxylase activity did not increase until 2 days after exercise. The mRNA levels for the fibrillar collagens (I and III) and basement membrane type IV collagen significantly increased 1 day and 12 h after exertion, respectively. Peak mRNA levels were observed 2–4 days after running, the increases being more pronounced in MQF than in MS. No significant changes were observed in types I or III collagen at the protein level. Strenuous downhill running thus causes an increase in gene expression for collagen types I and III and their post-translational modifying enzymes in skeletal muscle in a co-ordinated manner. These changes, together with the increased gene expression of type IV collagen, may represent the regenerative response of muscle extracellular matrix to exercise-induced injury and an adaptive response to running exertion.

Interrelationships between muscle structure, muscle strength, and running economy.

PURPOSE The present study was designed to investigate possible differences in running economy (RE) among elite middle-distance runners by examining muscle structure and maximal isometric force (MVC). METHODS Ten young male runners ran at six different running speeds. During the running bouts, respiratory gases, and blood lactate were measured. Muscle biopsies were obtained from the vastus lateralis muscle for analyzing fiber type distribution, muscle fiber area, myosin heavy chain (MHC) composition, activities of a number of metabolic enzymes (citrate synthase, lactate dehydrogenase, phosphofruktokinase, and 3-hydroxyacyl-CoA-dehydrogenase), and titin isoforms. RESULTS Energy expenditure (EE) increased linearly up to the speed of 6.0 m.s. The relative distribution of the MHC isoforms was MHC I: 67.0%, MHC IIA: 31.5%, and MHC IIX: 1.5%. The present results demonstrated that higher the area of Type II fibers, higher the MVC (r = 0.59, P< 0.05). The amount of MHC II correlated inversely with EE when running close to the competition speed (r = -0.61, P< 0.05). Enzyme activities did not correlate significantly with either RE or EE. Titin analysis revealed that a faster-mobility titin band was observed in all subjects, whereas a lower-mobility titin band was observed only in the most economical runner. CONCLUSION Differences in RE among homogeneous group of middle-distance runners were observed at various running speeds. This may partly be explained by differences in muscle fiber distribution, MHC composition, and titin isoforms.

Type IV collagen and its degradation in paralyzed human muscle: Effect of functional electrical stimulation

The purpose of this study was to evaluate the effects of spinal cord injury (SCI) and functional electrical stimulation (FES) of paralyzed muscles on type IV collagen content and proteins involving its degradation, which is initiated by matrix metalloproteinase (MMP)‐2 and ‐9 and regulated by their tissue inhibitors (TIMPs)‐2 and ‐1. Ten SCI subjects participated in an 18‐month program of functional electrical stimulation (FES) of their leg muscles. Needle biopsies were taken from the vastus lateralis muscle before and at various times during the training period, and from able‐bodied controls. Type IV collagen concentration was unaltered. ProMMP‐2 level of SCI subjects before the training period tended to be higher than able‐bodied controls and was significantly above the control level after FES. MMP‐9 concentration was unchanged. The results suggest accelerated type IV collagen turnover in skeletal muscle of SCI individuals especially after FES as a part of adaptive process of the muscle.

Determinants of Lower-Body Muscle Power in Early Postmenopausal Women

Objectives: To investigate the association between muscle size, density, and fiber composition; body composition; maximal isometric knee extension strength (KES); and lower‐body muscle power in healthy postmenopausal women.