Patients with unilateral renal/ureteral calculosis who had suffered a few painful attacks were examined. In the pain-free period, muscular, subcutaneous and cutaneous sensory thresholds to electrical stimulation were measured in the lumbar region (metamer L1) on both sides: (1) pain thresholds were lower on the affected side with respect to both the contralateral side and control thresholds recorded in normal subjects; (2) the greatest decrease in threshold was in the muscle (even the sensation of sustained contraction was no longer detectable), followed by subcutaneous tissue, and the smallest decrease was in the skin.

Eccentric muscle effort is known to induce delayed muscle soreness (DOMS) and muscle damage which are not responsive to medical treatment with the most common analgesic agents. The aim of the study was to investigate the effects of oral L-carnitine supplementation on pain (VAS scale), tenderness (pain thresholds) and CK release induced by a 20-min eccentric effort of the quadriceps muscle. A single-blind study was carried out on 6 untrained subjects (mean age: 26 +/- 3.8 yrs; mean height: 173 +/- 4.6 cm; mean body weight, 68.3 +/- 4.5 kg) over 7 weeks during which each subject: a) was given 3 g/day of placebo for 3 weeks and, after a week's interval, 3 g/day of L-carnitine for 3 weeks: b) performed 2 step tests on the first day of the 3rd and 7th week inverting the order of the exercising limb. In a separate set of experiments carried out 8 months later, the possible effects of training on pain parameters and CK levels were also investigated in the same subjects who performed 2 step tests at a 4-weeks' interval, without medication. L-carnitine significantly reduced pain, tenderness and CK release after the effort with respect to placebo. In contrast, no significant difference was found in the parameters measured between the two tests performed without medication. It is concluded that L-carnitine has a protective effect against pain and damage from eccentric effort. This effect is mainly attributed to the vasodilatation property of the compound, which both improves energetic metabolism of the hypoxic/damaged muscle and enhances wash-out of algogenic metabolites.

After the induction of an experimental algogenic focus in the left brachioradialis muscle of 15 healthy subjects, the algosensitive thresholds of the cutaneous, subcutaneous, and muscular tissues are studied in the painful region by means of electrical stimulation. Statistical analysis of the results shows (a) normal sensory thresholds in the three structures; (b) significantly lowered pain thresholds in a limited ellipsoid area in the skin and subcutaneous tissue and in the whole painful area in the muscle. These results clearly indicate a hyperalgesic condition in the parietal layers of the area examined.

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