Kazunori Nosaka

MUSCLE FUNCTION AFTER EXERCISE-INDUCED MUSCLE DAMAGE AND RAPID ADAPTATION

This brief review focuses on the time course of changes in muscle function and other correlates of muscle damage following maximal effort eccentric actions of the forearm flexor muscles. Data on 109 subjects are presented to describe an accurate time course of these changes and attempt to establish relationships among the measures. Peak soreness is experienced 2-3 d postexercise while peak swelling occurs 5 d postexercise. Maximal strength and the ability to fully flex the arm show the greatest decrements immediately after exercise with a linear restoration of these functions over the next 10 d. Blood creatine kinase (CK) levels increase precipitously at 2 d after exercise which is also the time when spontaneous muscle shortening is most pronounced. Whether the similarity in the time courses of some of these responses implies that they are caused by similar factors remains to be determined. Performance of one bout of eccentric exercise produces an adaptation such that the muscle is more resistant to damage from a subsequent bout of exercise. The length of the adaptation differs among the measures such that when the exercise regimens are separated by 6 wk, all measures show a reduction in response on the second, compared with the first, bout. After 10 wk, only CK and muscle shortening show a reduction in response. After 6 months only the CK response is reduced. A combination of cellular factors and neurological factors may be involved in the adaptation process.

Changes in indicators of inflammation after eccentric exercise of the elbow flexors

This study examined muscle swelling and changes in inflammatory markers in the blood following eccentric exercise-induced muscle damage. Subjects (N = 14) who had not been involved in a resistance training program performed 24 maximal eccentric actions of the elbow flexors. Muscle swelling was assessed by measures of the upper arm circumference (CIR), ultrasonography (USG), and magnetic resonance imaging (MRI). Plasma concentrations of interleukin-1 alpha, interleukin-1 beta, interleukin-2, interleukin-6, tumor necrosis factor-alpha, and plasma levels of C-reactive protein, cortisol, and zinc were analyzed. Established indicators of muscle damage (maximal isometric force, range of motion, muscle soreness, and plasma creatine kinase, aspartate aminotransferase, and lactate dehydrogenase activities) were also measured. All measures, including CIR and USG, except for MRI, were assessed immediately before and after and for 5 d post-exercise. MRI was taken at pre- and 1, 3, 6, 10, 23, 31, and 58 d post-exercise. All muscle damage indicators changed significantly after exercise. A large increase in CIR (> 20 mm) was found 4-5 d after exercise, and this coincided with USG, showing an increase in muscle thickness. The echointensity of USG increased with the enlargement of the elbow flexors. MRI displayed enlargement of the biceps brachii and brachialis cross-sectional area that started at 1 d, and lasted until 23 d, post-exercise. The most profound increase in the enlargement and signal intensity of the MRI was found 3 or 6 d after exercise. However, none of the plasma levels of inflammatory makers showed significant muscle swelling, which is indicative of muscle edema, but the inflammatory responses after exercise appear to be different from those accompanying infection or tissue injury.

Delayed‐onset muscle soreness does not reflect the magnitude of eccentric exercise‐induced muscle damage

This study investigated the relationship between delayed‐onset muscle soreness and other indicators of muscle damage following eccentric exercise. Male students (n = 110) performed 12 (12ECC), 24 (24ECC), or 60 maximal eccentric actions of the elbow flexors (60ECC). Maximal isometric force, relaxed and flexed elbow joint angles, upper arm circumference, and plasma creatine kinase activity were assessed immediately before and after, and for 4 days after exercise. Muscle soreness (SOR) was evaluated by a visual analog scale (a 50‐mm line, 0: no pain, 50: extremely painful) when the elbow flexors were palpated (SOR–Pal), flexed (SOR–Flx) and stretched (SOR–Ext). Although 24ECC and 60ECC resulted in significantly (P <; 0.05) larger changes in all indicators and slower recovery compared to 12ECC, no significant differences were evident for SOR–Pal and SOR–Flx between 12ECC and 24ECC, or 12ECC and 60ECC. In contrast, SOR–Ext was significantly (P <; 0.05) lower for 12ECC compared to 24ECC and 60ECC. A Pearson product‐moment correlation showed SOR–Pal did not correlate significantly with any indicators, however, SOR–Ext and SOR–Flx showed weak (r <; 0.32) but significant (P <; 0.05) correlations with other indicators. Because of generally poor correlations between DOMS and other indicators, we conclude that use of DOMS is a poor reflector of eccentric exercise‐induced muscle damage and inflammation, and changes in indirect markers of muscle damage and inflammation are not necessarily accompanied with DOMS.

How long does the protective effect on eccentric exercise-induced muscle damage last?

PURPOSE One bout of eccentric exercise produces an adaptation that reduces muscle damage in subsequent bouts. Because it is not known how long this adaptation lasts, the present study investigated the maximal length of the attenuated changes in muscle damage indicators after high-force eccentric exercise. METHODS Male students (N = 35) were placed into three groups and performed two bouts of eccentric exercise of the nondominant elbow flexors separated by either 6 (N = 14), 9 (N = 11), or 12 (N = 10) months. Maximal isometric force (MIF), range of motion (ROM), upper arm circumference (CIR), muscle soreness (SOR), and plasma creatine kinase activity (CK) were measured before and for 5 d after exercise. Magnetic resonance (MR) images of the transverse and longitudinal scans of the upper arm were taken 4 d after exercise. Changes in the criterion measures were compared between the first and second bouts and between groups by a two-way repeated measures ANOVA. RESULTS A faster recovery in MIF was evident after a second bout performed at 6 or 9 months, and reduced SOR as well as smaller increases in CIR, CK, and T2 relaxation time of MR images also occurred after the second exercise bout at 6 months compared with initial responses. No significant differences between the bouts were found for ROM, and the 12-month group did not show any repeated bout effect. CONCLUSION These results show that the repeated bout effect for most of the criterion measures lasts at least 6 months but is lost between 9 and 12 months.

Exercise-induced muscle damage, plasma cytokines, and markers of neutrophil activation

INTRODUCTION Unaccustomed eccentric exercise often results in muscle damage and neutrophil activation. We examined changes in plasma cytokines stress hormones, creatine kinase activity and myoglobin concentration, neutrophil surface receptor expression, degranulation, and the capacity of neutrophils to generate reactive oxygen species in response to in vitro stimulation after downhill running. METHODS Ten well-trained male runners ran downhill on a treadmill at a gradient of -10% for 45 min at 60% VO2max. Blood was sampled immediately before (PRE) and after (POST), 1 h (1 h POST), and 24 h (24 h POST) after exercise. RESULTS At POST, there were significant increases (P < 0.01) in neutrophil count (32%), plasma interleukin (IL)-6 concentration (460%), myoglobin (Mb) concentration (1100%), and creatine kinase (CK) activity (40%). At 1 h POST, there were further increases above preexercise values for neutrophil count (85%), plasma Mb levels (1800%), and CK activity (56%), and plasma IL-6 concentration remained above preexercise values (410%) (P < 0.01). At 24 h POST, neutrophil counts and plasma IL-6 levels had returned to baseline, whereas plasma Mb concentration (100%) and CK activity (420%) were elevated above preexercise values (P < 0.01). There were no significant changes in neutrophil receptor expression, degranulation and respiratory burst activity, and plasma IL-8 and granulocyte-colony stimulating factor concentrations at any time after exercise. Neutrophil count correlated with plasma Mb concentration at POST (r = 0.64, P < 0.05), and with plasma CK activity at POST (r = 0.83, P < 0.01) and 1 h POST (r = 0.78, P < 0.01). CONCLUSION Neutrophil activation remains unchanged after downhill running in well-trained runners, despite increases in plasma markers of muscle damage.

Time course of muscle adaptation after high force eccentric exercise.

SummaryThe repeated bout effect on changes in muscle damage indicators was examined in two groups of subjects following two bouts of 70 maximal eccentric actions of the forearm flexors. Fourteen college age female subjects were placed into two groups. The two bouts were separated by 6 weeks (n=6), and 10 weeks (n = 8). The subjects performed the same amount of work for the bouts. The muscle damage indicators were isometric strength (STR), relaxed elbow joint angle (RANG), flexed elbow joint angle (FANG), perceived muscle soreness ratings (SOR), and plasma creatine kinase activity (CK). These measures were obtained pre-exercise and 5 days following each bout. The first bout showed significant changes in all measures over time for both groups (P<0.01). For the 6-week group, significantly smaller changes in RANG (P < 0.01), SOR (P<0.05), and CK (P<0.01), as well as significantly faster recoveries (P<0.05) for STR and FANG were produced in the second bout. For the 10-week group, significantly smaller changes in RANG (P<0.05) and CK (P<0.01) were demonstrated by the second bout, but no significant difference was found for STR, FANG, and SOR between bouts 1 and 2. Changes in CK were still significantly smaller than that of the first bout when 6 subjects (3 subjects from each group) performed the same exercise 6 months after the second bout, but no difference in other measures. It is concluded that the length of the adaptation effect varies among the indicators of muscle damage and that the duration of the adaptation for CK is dramatic.

Effect of elbow joint angle on the magnitude of muscle damage to the elbow flexors

PURPOSE It has been shown that eccentric actions at a long muscle length result in a larger decrease in force and more muscle tenderness compared with those at a short muscle length. To further investigate the effect of elbow joint angle on the development of muscle damage, this study compared two maximal eccentric exercise regimens in which the starting position of the action was different, but the range of movement was the same. METHODS One arm of 10 male students performed 24 maximal eccentric actions of the elbow flexors at the elbow joint angle from 0.87 to 2.27 rad (50-130 degrees: S condition) and the other arm at the elbow joint angle from 1.74 to 3.14 rad (100-180 degrees: L condition). Maximal isometric force, range of motion, muscle soreness, plasma creatine kinase activity, upper arm circumference, and B-mode ultrasound pictures of the elbow flexors (US) were measured before and for 5 d postexercise in both conditions. Magnetic resonance imaging (MRI) of the transverse scans of the upper arm was taken at 4 d after exercise. RESULTS All measures changed significantly (P < 0.01) after exercise for both conditions; however, significantly (P < 0.01) larger changes in the measures were found in the L condition compared with the S condition. MRI and US displayed that only the brachialis was damaged for the S condition but the biceps brachii was also damaged for the L condition. CONCLUSION The greater development of muscle damage in the L condition compared with the S condition is likely to be associated with the elbow flexors muscles affected by the exercise.

Ice Slurry Ingestion Increases Core Temperature Capacity and Running Time in the Heat

PURPOSE To investigate the effect of ice slurry ingestion on thermoregulatory responses and submaximal running time in the heat. METHODS On two separate occasions, in a counterbalanced order, 10 males ingested 7.5 g·kg(-1) of either ice slurry (-1°C) or cold water (4°C) before running to exhaustion at their first ventilatory threshold in a hot environment (34.0°C ± 0.2°C, 54.9% ± 5.9% relative humidity). Rectal and skin temperatures, HR, sweating rate, and ratings of thermal sensation and perceived exertion were measured. RESULTS Running time was longer (P = 0.001) after ice slurry (50.2 ± 8.5 min) versus cold water (40.7 ± 7.2 min) ingestion. Before running, rectal temperature dropped 0.66°C ± 0.14°C after ice slurry ingestion compared with 0.25°C ± 0.09°C (P = 0.001) with cold water and remained lower for the first 30 min of exercise. At exhaustion, however, rectal temperature was higher (P = 0.001) with ice slurry (39.36°C ± 0.41°C) versus cold water ingestion (39.05°C ± 0.37°C). During exercise, mean skin temperature was similar between conditions (P = 0.992), as was HR (P = 0.122) and sweat rate (P = 0.242). After ice slurry ingestion, subjects stored more heat during exercise (100.10 ± 25.00 vs 78.93 ± 20.52 W·m(-2), P = 0.005), and mean ratings of thermal sensation (P = 0.001) and perceived exertion (P = 0.022) were lower. CONCLUSIONS Compared with cold water, ice slurry ingestion lowered preexercise rectal temperature, increased submaximal endurance running time in the heat (+19% ± 6%), and allowed rectal temperature to become higher at exhaustion. As such, ice slurry ingestion may be an effective and practical precooling maneuver for athletes competing in hot environments.

Does Performance of Hang Power Clean Differentiate Performance of Jumping, Sprinting, and Changing of Direction?

The primary purpose of this study was to investigate whether the athlete who has high performance in hang power clean, a common weightlifting exercise, has high performances in sprinting, jumping, and changing of direction (COD). As the secondary purpose, relationships between hang power clean performance, maximum strength, power and performance of jumping, sprinting, and COD also were investigated. Twenty-nine semiprofessional Australian Rules football players (age, height, and body mass [mean ± SD]: 21.3 ± 2.7 years, 1.8 ± 0.1 m, and 83.6 ± 8.2 kg) were tested for one repetition maximum (1RM) hang power clean, 1RM front squat, power output during countermovement jump with 40-kg barbell and without external load (CMJ), height of CMJ, 20-m sprint time, and 5-5 COD time. The subjects were divided into top and bottom half groups (n = 14 for each group) based on their 1RM hang power clean score relative to body mass, then measures from all other tests were compared with one-way analyses of variance. In addition, Pearsons product moment correlations between measurements were calculated among all subjects (n = 29). The top half group possessed higher maximum strength (P < 0.01), power (P < 0.01), performance of jumping (P < 0.05), and sprinting (P < 0.01). However, there was no significant difference between groups in 5-5 COD time, possibly because of important contributing factors other than strength and power. There were significant correlations between most of, but not all, combinations of performances of hang power clean, jumping, sprinting, COD, maximum strength, and power. Therefore, it seems likely there are underlying strength qualities that are common to the hang power clean, jumping, and sprinting.

Concentric or eccentric training effect on eccentric exercise-induced muscle damage

PURPOSE The purpose of this study was to compare changes in muscle damage indicators following 24 maximal eccentric actions of the elbow flexors (Max-ECC) between the arms that had been previously trained either eccentrically or concentrically for 8 wk. METHODS Fifteen subjects performed three sets of 10 repetitions of eccentric training (ECC-T) with one arm and concentric training (CON-T) with the other arm once a week for 8 wk using a dumbbell representing 50% of maximal isometric force of the elbow flexors (MIF) determined at the elbow joint of 90 degrees (1.57 rad). The dumbbell was lowered from a flexed (50 degrees, 0.87 rad) to an extended elbow position (180 degrees, 3.14 rad) in 3 s for ECC-T, and lifted from the extended to the flexed position in 3 s for CON-T. Max-ECC was performed 4 wk after CON-T and 6 wk after ECC-T. Changes in MIF, range of motion (ROM), upper arm circumference (CIR), muscle soreness (SOR), and plasma creatine kinase (CK) activity were compared between the ECC-T and CON-T arms. RESULTS The first ECC-T session produced larger decreases in MIF and ROM, and larger increases in CIR and SOR compared with CON-T. CK increased significantly (P < 0.01) and peaked 4 d after the first training session, but did not increase in the following sessions. All measures changed significantly (P < 0.01) following Max-ECC; however, the changes were not significantly different between ECC-T and CON-T arms. CONCLUSION These results showed that ECC-T did not mitigate the magnitude of muscle damage more than CON-T, and CON-T did not exacerbate muscle damage.