The thermal effects of shortening in tetanic contractions of frog muscle.

1. In tetanic contractions during which shortening has occurred the total heat produced is greater than in isometric controls.2. The amount of this excess, measured after relaxation, is less than the shortening heat measured before relaxation. In other words relaxation heat is less after contractions with shortening.3. Only a small part of this reduction in relaxation heat can be explained by the reduced thermoelastic heat and work dissipation due to the lower tension maintained after shortening.4. In the few experiments in which the full tension is redeveloped after shortening the relaxation heat is still reduced.5. Decreases in the tension redeveloped after shortening, caused by using shorter tetani, or slower shortening, are not accompanied by decreases in the relaxation heat greater than can be accounted for by the assumed physical results of the lower tension.6. It is suggested that the reduction in relaxation heat after shortening is due to the occurrence of a reaction in which the exothermic process causing the shortening heat is reversed.

Supplement use, other dietary and demographic variables, and serum vitamin C in NHANES II.

OBJECTIVE: Our objective was to evaluate the effect of regular use of nutritional supplements on serum vitamin C levels in a multivariable regression model, taking into account other dietary and demographic variables which may affect nutritional status. METHODS: We analyzed NHANES II data for subjects age 3 to 74. Analysis was limited to regular supplement users and nonusers, excluding irregular users. Multivariable regression analysis was performed with SUDAAN, incorporating sample weights and accounting for the complex survey design. RESULTS: Regular supplement users had substantially higher serum vitamin C levels than nonusers (p < 0.001). The magnitude of the effect of supplement use on serum vitamin C was 0.23-0.33 mg/dL in children and teens, and 0.36-0.46 mg/dL in adults. In adults who smoked, bottom quartile vitamin C levels were 0.3 mg/dL in men and 0.4 mg/dL in women who did not use supplements, compared to 0.9 and 1.1 mg/dL in regular supplement users. There was a significant interaction of smoking and supplement use in men (p < 0.001). CONCLUSION: Regular supplement use has a strong impact on serum vitamin C levels, independent of other dietary and demographic characteristics of supplement users which may favor improved nutritional status.