Skeletal muscle growth in young rats is inhibited by chronic exposure to IL-6 but preserved by concurrent voluntary endurance exercise.

Childhood diseases are often accompanied by chronic inflammation, which is thought to negatively impact growth. Interleukin-6 (IL-6) is typically cited as an indicator of inflammation and is linked to impaired growth. This study was designed to isolate and identify potential effects of chronic IL-6 exposure on skeletal muscle growth during development. A second aim was to determine if endurance exercise, thought to antagonize chronic inflammation, would interact with any effects of IL-6. The muscles of one leg of rapidly growing rats were exposed to IL-6 or vehicle for 14 days. Subgroups of IL-6-infused rats were provided access to running wheels. Local IL-6 infusion resulted in approximately 13% muscle growth deficit (myofibrillar protein levels). Exercise (>4,000 m/day) prevented this deficit. IL-6 infusion increased mRNA for suppressor of cytokine signaling-3 (SOCS3) and tumor necrosis factor-alpha (TNF-alpha), and this was not prevented by exercise. IL-6 infusion increased the mRNAs for atrogin, insulin-like growth factor-I (IGF-I), and IGF binding protein-4 (IGFBP4), and these effects were mitigated by exercise. Exercise stimulated an increase in total RNA ( approximately 19%) only in the IL-6-infused muscle, suggesting that a compensatory increase in translational capacity was required to maintain muscle growth. This study indicates that IL-6 exposure during periods of rapid growth in young animals can retard growth possibly via interactions with key growth factors. Relatively high volumes of endurance-type exercise do not exacerbate the negative effects of IL-6 and in fact were found to be beneficial in protecting muscle growth.

Tetracycline therapy for muscle atrophy due to immobilization.

Certain proteins such as matrix metalloproteinase -2(MMP-2) and heat shock protein 70(HSP-70) play a role during the degradation process. We hypothesized that tetracycline can be used to reduce tissue degradation in skeletal muscles exposed to immobilization. The right knee of old rats (20-months-old) was immobilized by a rigid external fixator (EF) device for 1, 2, 3 and 4 weeks. Aqueous Tetracycline solution was administrated 3 times a week, following 2 days after the EF was constructed. Control group I was immobilized for 3 weeks, did not receive tetracycline but did received saline injection, and control group II only received tetracycline for 3 weeks. MMP-2 and HSP-70 protein and mRNA levels in the gastrocnemius and soleus muscles were analyzed at the molecular level by RT-PCR and the protein level using SDS-PAGE gels and western blots. We have shown that rats treated by Tetracycline reduce the MMP-2 expression and HSP-70. Theses changes mainly occurred in type IIb and type IIa muscle fibers. Tetracycline administration has beneficial effect on expression of enzymes involved in protein degradation. This may suggest a protective effect on protein degradation during immobilization.

Using virtual reality simulation to study navigation in a complex environment as a functional-cognitive task; A pilot study.

BACKGROUND: Navigation skills are required for performance of functional complex tasks and may decline due to aging. Investigation of navigation skills should include measurement of cognitive-executive and motor aspects, which are part of complex tasks. OBJECTIVE: to compare young and older healthy adults in navigation within a simulated environment with and without a functional-cognitive task. METHODS: Ten young adults (25.6±4.3 years) and seven community dwelling older men (69.9±3.8 years) were tested during a single session. After training on a self-paced treadmill to navigate in a non-functional simulation, they performed the Virtual Multiple Errands Test (VMET) in a mall simulation. Outcome measures included cognitive-executive aspects of performance and gait parameters. RESULTS: Younger adults' performance of the VMET was more efficient (1.8±1.0) than older adults (5.3±2.7; p < 0.05) and faster (younger 478.1±141.5 s, older 867.6±393.5 s; p < 0.05). There were no differences between groups in gait parameters. Both groups walked slower in the mall simulation. CONCLUSIONS: The shopping simulation provided a paradigm to assess the interplay between motor and cognitive aspects involved in the efficient performance of a complex task. The study emphasized the role of the cognitive-executive aspect of task performance in healthy older adults.

Light touch and medio-lateral postural stability during short distance gait.

While standing, light fingertip touch on an external stable object attenuates sway and improves balance in healthy adults as well as in individuals with poor postural control. The effect of light touch on balance during gait is, however, not well known. Therefore, the purpose of this work was to study the effects of light fingertip touch on balance during gait. We hypothesized that similar to its effect during stance light touch would increase postural stability. Forty healthy young adults were tested under four gait conditions: (1) eyes open (EO), (2) eyes closed (EC), (3) eyes closed while lightly touching a static object on the right side of the walking lane (ECLTS), (4) eyes closed while lightly touching a dynamic object, namely, a stick that was moved forwards by the subject with the right hand (ECLTD). The main outcome measure was medio-lateral step width variability, a well established indicator of gait balance in the medio-lateral plane. During the EC condition, light touch of an external static object (ECLTS) decreased medio-lateral variability (i.e., balance improved); however, this stabilizing effect was not observed with light touch on the stick. The availability of self positional and spatial cues when touching a static external reference, and their absence when touching a stick that is moved forwards by the subject as he walks, can explain the different effects of light touch in the ECLTS vs the ECLTD gait conditions.

Expression of superoxide dismutase and matrix metalloproteinase type 2 in diaphragm muscles of young rats.

Moderate physical activity increases antioxidant defenses, whereas intensive activity is associated with oxidative stress. In this study we investigated the expression of superoxide dismutase (Cu,Zn-SOD), a major antioxidant defense enzyme, and that of the proteolytic enzyme matrix metalloproteinase-2 (MMP-2) in exercising muscle tissue. Treadmill running was used as a model to investigate the mechanism involved in muscle use and over use. Sprague-Dawley female rats (4 months old) were randomly assigned to 3 groups: running group I, trained at a slow speed (18 m/min; approximately 50% VO(2)), running group II, trained at a very fast speed (32 m/min; approximately 75% VO(2)), for 3 weeks, and group III - control, non-running group. Cu,Zn-SOD was measured spectrophotometrically at 320 nm by assessing the inhibition of cytochrome c reduction by xanthine oxidase. MMP-2 levels of protein and mRNA were assessed in the diaphragm by Western blotting and by reverse transcriptase-polymerase chain reaction, respectively. We found that Cu,Zn-SOD level significantly decreased in the crural diaphragm muscle of rats three weeks after fast speed running, whereas it remained unchanged in the sternal diaphragm muscle three weeks after slow speed running. The expression of MMP-2 increased in both fast and slow running groups; however, it was particularly prominent in the fast twitch muscle fibers type IIb. We conclude that the crural diaphragm muscle, which contains significantly more type IIb fibers, was more affected following fast speed running than the sternal/costal diaphragm muscles, which have an equal distribution of slow twitch (type I) and fast twitch (type IIb) muscle fibers.

Neutrophil function response to aerobic and anaerobic exercise in female judoka and untrained subjects.

OBJECTIVES: Recent studies have indicated reduced immunity in trained athletes. AIM: To assess the effects of aerobic and anaerobic exercise on the phagocytic process in 18-26 year old trained female judoka (n = 8) and untrained controls (n = 7). METHODS: Each subject participated randomly in two different testing sessions (aerobic, 20 minutes of treadmill running at 70-80% of maximal heart rate; anaerobic, Wingate anaerobic test). Venous blood samples were drawn before, immediately after, and 24 hours after each session. RESULTS: There were no significant differences in basal values of net chemotaxis (chemotaxis--random migration), bactericidal activity, and superoxide anion release between the judoka and the untrained women. There was a significant decrease in net chemotaxis 24 hours after the aerobic exercise in both the judoka (from 64 (19) to 39 (13) cells/field, p < 0.02) and the untrained controls (from 60 (7) to 47 (12) cells/field, p < 0.05). Bactericidal activity and superoxide anion release did not change significantly after aerobic exercise in either group. There were no significant changes in net chemotaxis, bactericidal activity, and superoxide anion release after anaerobic exercise in either the judoka or untrained women. CONCLUSIONS: The decrease in net chemotaxis after aerobic, but not after anaerobic, exercise, suggests that net chemotaxis is affected by the combination of exercise intensity and duration, and not by the exercise intensity itself. Similar effects of both exercise sessions in the judoka and the untrained women suggest that training had no effect on neutrophil function response to aerobic and anaerobic exercises.

Aspects of leukocyte function and the complement system following aerobic exercise in young female gymnasts.

Recent studies have reported reduced immunity in trained athletes. Scant information exists on changes in the immune function among trained children. The purpose of this study was to assess the effect of aerobic exercise on the phagocytic process of neutrophils and the complement system in young athletes. Subjects included prepubertal elite female gymnasts (n = 7) and untrained girls (n = 6) aged 10-12 years. Venous blood was withdrawn before, immediately post and 24 h following a 20-min run at a heart rate of 170-180 beats.min-1. Neutrophil random migration, chemotactic activity, bactericidal function and PMA/FMLP-stimulated superoxide anion release as well as various complement components were assessed. Net chemotaxis was found reduced (P < 0.05) 24 h following exercise (58 +/- 11 vs. 36 +/- 11 cells/field in gymnasts and 47 +/- 7 vs. 42 +/- 8 cells/field in untrained girls pre- and 24 h post-exercise, respectively). The basal values, as well as post-exercise values of bactericidal activity were lower (P < 0.05) in gymnasts as compared with the control group (0.8 +/- 0.3, 0.8 +/- 0.2 and 0.8 +/- 0.1 log decrease of colonies in gymnasts at pre-, immediately post-, and 24 h post-exercise, respectively and 1.1 +/- 0.1, 1.1 +/- 0.1 and 1.0 +/- 0.2 log decrease of colonies in controls, respectively). No significant effect on the bactericidal activity was observed in either group following exercise. The addition of homologous sera did not correct the bactericidal activity. PMA-stimulated superoxide anion release decreased (P < 0.05) among gymnasts immediately following exercise (5.7 +/- 0.4 vs. 4.4 +/- 1.0 mmol O2/10(6) PMN.min) and remained low 24 h later. The same trend was observed in FMLP-stimulated neutrophils but the data were not significant. Significantly decreased levels (P < 0.05) of the early complement components (C1Q, C1R) were also found following exercise (1.34 +/- 0.64 vs. 1.27 +/- 0.28 and 1.09 +/- 0.07 vs. 1.02 +/- 0.06 pre- and post-exercise in gymnasts and untrained, respectively). Furthermore, consistently lower C2 and C3 were observed in gymnasts compared with controls. Neutrophil dysfunction as well as impairment of the complement system seem to occur following exercise.

Cellular and humoral immune response to exercise among gymnasts and untrained girls.

Recent studies reported reduced immunity in athletes following exercise. Physical activity affects both cellular and humoral immune functions. Scant information exists on exercise-induced changes in the immune system among children. The purpose of the present study was to investigate the effect of aerobic exercise on several aspects of cellular and humoral functions among 10-12 year-old highly trained female gymnasts (n = 7) and untrained girls (n = 6). All girls were pre-pubertal. Venous blood samples were drawn before, immediately after and 24 h following 20 min of treadmill running (heart rate 170-180 beats.min-1). White blood cells' number rose significantly following exercise and remained elevated for 24 h. The increase in leukocyte number was due to an increase in granulocytes as well as an increase in lymphocytes and monocytes. While neutrophil count returned to basal values after 24 h, lymphocytes and monocytes number remained elevated 24 h following exercise. Exercise resulted in a significant elevation of T cell lymphocytes, T helpers, T suppressors and natural killer cells. All values returned to normal after 24 h. There were no changes in B cell lymphocytes following exercise. Exercise had no effect on serum IgA, IgM, IgE, IgG and sub-types of IgG (IgG1, IgG2, IgG3 and IgG4). No differences were observed between gymnasts and untrained girls. In summary, the exercise-induced changes in cellular and humoral immune functions among the girls were generally similar to those described in adults. Whether the transitory effects of exercise on the immune system are related to increased susceptibility to illness is still questionable.