This study determined if insulin resistance (IR), induced by an acute bout of eccentrically-biased contractions that resulted in muscle injury, was attenuated following a repeated bout of contractions. Female subjects (n = 10, age 24.7 ± 3.0 yr, weight 64.9 ± 7.4 kg, height 1.67 ± 0.02 m, body fat 29.1 ± 1.9 %) performed two 30 minute bouts of downhill treadmill running (DTR 1 and DTR 2, -12 % grade, 8.0 mph) separated by 14 days. Oral glucose tolerance tests (OGTT) were administered at baseline and 48 hours following DTR 1 and DTR 2, with IR assessed by calculation of insulin and glucose areas under the curve (AUC). Maximum isometric quadriceps strength (MVC), muscle soreness (SOR), and serum creatine kinase (CK) were assessed pre-, immediately post-, and 48 hours post-DTR 1 and DTR 2 to determine the presence of muscle injury. Compared to baseline OGTT, insulin and glucose AUC (37.6 ± 8.4 and 21.4 ± 4.7 % increase, respectively), and peak insulin (44.1 ± 5.1 vs. 31.6 ± 4.0 uU·mL-1) and glucose (6.5 ± 0.4 vs. 5.5 ± 0.4 mmol·L-1) were elevated following DTR 1. These same insulin and glucose measures showed no increase above baseline 48 hours following DTR 2 (p > 0.05). MVC was reduced to a greater degree immediately following DTR 1 (16.7 ± 2.6 vs. 8.6 ± 1.2 % decline) and, although demonstrating a significant degree of recovery, remained reduced by 9.4 ± 2.7 % 48 hours following exercise. In contrast, MVC made a full recovery back to baseline values 48 hours after DTR 2. SOR was elevated to a greater degree 48 hours following DTR 1 than after DTR 2 (48.08 ± 6.16 vs. 12.70 ± 3.24 mm). There was a tendency for an attenuated serum CK response 48 hours following DTR 2 (812.8 ± 365.1 vs. 162.5 ± 42.5 U·L-1, p = 0.08). In conclusion, a novel bout of eccentrically-biased contractions resulting in a moderate degree of muscle injury confers a protective effect, whereby a subsequent bout of contractions 14 days later results in complete elimination of the IR observed following the initial bout.

Supporters of a nutritional supplement, β-Hydroxy-β-Methylbutyrate (HMB) supplementation, claim that it will increase the muscular strength gains and lean muscle mass gains seen during a resistance training program. It has been suggested that HMB supplementation does this by preventing muscle damage or by regenerating damaged muscle cell membranes. However, no research has evaluated the effect of HMB supplementation on low frequency fatigue. Therefore, the purpose of this study was to determine if three weeks of HMB supplementation could attenuate the effects of low frequency fatigue caused by eccentric muscle contractions of the tibialis anterior muscle. A total of 33 healthy recreationally active subjects (18 males, 15 females; 23.2 ± 4.3 yr) were recruited for this study. All subjects preformed 4 sets of 25 eccentric contractions of the tibialis anterior muscle through a range of motion of 30 degrees. Recovery measures were taken for 20 minutes after the fatigue protocol and at 48 and 96 hours of recovery. The recovery measures included: Maximum voluntary contraction peak torque, 10 Hz peak torque, 50 Hz peak torque, 10/50 Hz peak torque ratio, and EMG measurements. Each subject served as their own control and limbs were randomly assigned to pre-supplement or post-supplement limbs. Following the pre-supplement fatigue protocol and recovery measures each subject completed three weeks of 3g/day HMB supplementation. After the supplementation period the post-supplement fatigue protocol was completed and recovery measures were taken. The 10 Hz peak torque and the 10/50 Hz torque ratio in the pre-supplement limb was still significantly reduced at the 96-hour recovery measurement time, indicating that it was still showing low frequency muscle fatigue at this time. Furthermore, the post-supplement limb, recovered from the fatigue protocol faster, and did not show any signs of low frequency muscle fatigue at the 48-hour recovery measurement time. In addition the pre-supplement limb had significant maximum voluntary contraction torque deficit at the 48-hour recovery measurement time and the post-supplement limb showed no significant deficits. The main findings of this study were that three weeks of HMB supplementation attenuated low frequency fatigue and maximum voluntary contraction torque reduction after an eccentric fatigue protocol.

No description available.

Exercise-induced muscle soreness is characterized by stiffness, tenderness and pain during active movements and weakness of the affected musculature the days after unusually or particularly heavy work. The most pronounced subjective symptoms do not arise immediately but rather between a couple of hours to some days after the exercise (a delayed-onset of muscle soreness), the intensity of pain is greatest about 48 hours after the work. A particular association exists between muscle soreness and eccentric contractions. Despite the fact that muscle soreness is a well known phenomenon in the sphere of sports as well as working life, the pathophysiological mechanisms underlying this are still not understood. In the present study a detailed analysis of human muscle fibre population structure after high tension work (eccentric exercise) that gave rise to muscle soreness, was carried out. The objective was to elucidate how fibres of different types are influenced by repeated muscle contractions reaching extreme tension levels using qualitative and quantitative light and electron microscopic techniques. It was hoped that such morphological analysis would provide a basis for discussion of possible causes for muscle soreness. The muscle function after the work was measured by isokinetic methods. To improve the basis for the ultrastructural analysis the fibre populations in untrained and en­durance trained human m. vastus lateralis of age-matched individuals were classified into different fibre type groups according to their ultrastructure. The selective glycogen depletion from Type 1 fibres seen after long term submaximal work, visualized electron microscopically with PA-TSC-SP staining, substantiated the usefulness of the appearance of the M-band to differentiate between fibre types. Stereological data showed that neither volume density of mitochondria nor of lipid droplets provide sufficient criteria to differentiate between fibre types. After an eccentric exercise regimen sore muscles (m. soleus or m. vastus lateralis) showed disturb­ances of the cross striated band pattern. Fibres with disorganized myofibrillar material made up 1/3, 1/2 and 1/10 of the analysed material, 1 hour, 3 and 6 days after exercise, respectively. The myofibril­lar lesions were preferably localized in the Z-band. This showed streaming, broadening and sometimes total disruption. The Type 2 fibres were most affected. The reduction of strength was greatest with the most rapid contractions. Strength remained de­creased the period when the structural damage was most pronounced. Eight weeks of eccentric muscle training reduced all the above negative effects. The results indicate that the Z-disc constitute the weak link in the myofibrillar contractile chain at high muscle tensions. It is suggested that the myofibrillar lesions are a direct result of mechanical tearing. Rupture of myofibrils is thought to result in formation of protein components and a con- sequental release of protein bound ions that via osmosis result in oedema and soreness. Training, using eccentric contractions over a long period of time leads to adaptations at the fibre level by a reorgani­zation of the contractile apparatus as well as an optimization of nervous coordination. / <p>S. 1-40: sammanfattning, s. 41-79: 5 uppsatser</p> / digitalisering@umu