As many of you know, I was going to do a Sherdogger's Guide to ZMA as an addendum to the FAQ; in my gathering of information, I've come across some dubious research regarding it's efficacy. I'm going to post what I have up here, and let the questions and discussion roll:
Eur J Clin Nutr. 2007 Sep 19 [Epub ahead of print]
Links
Serum testosterone and urinary excretion of steroid hormone ****bolites after administration of a high-dose zinc supplement.
Koehler K,
Parr MK,
Geyer H,
Mester J,
Schänzer W.
1Institute of Biochemistry, German Research Centre of Elite Sport, German Sport University Cologne, Cologne, Germany.
Objectives:To investigate whether the administration of the zinc-containing nutritional supplement ZMA causes an increase of serum testosterone levels, which is an often claimed effect in advertising for such products; to monitor the urinary excretion of testosterone and selected steroid hormone ****bolites to detect potential changes in the excretion patterns of ZMA users.Subjects:Fourteen healthy, regularly exercising men aged 22-33 years with a baseline zinc intake between 11.9 and 23.2 mg day(-1) prior to the study.
Results:Supplementation of ZMA significantly increased serum zinc (P=0.031) and urinary zinc excretion (P=0.035). Urinary pH (P=0.011) and urine flow (P=0.045) were also elevated in the subjects using ZMA. No significant changes in serum total and serum free testosterone were observed in response to ZMA use. Also, the urinary excretion pattern of testosterone ****bolites was not significantly altered in ZMA users.C
onclusions:The present data suggest that the use of ZMA has no significant effects regarding serum testosterone levels and the ****bolism of testosterone in subjects who consume a zinc-sufficient diet.European Journal of Clinical Nutrition advance online publication, 19 September 2007; doi:10.1038/sj.ejcn.1602899.
While this study pretty much shoots Conte's previous studies down, it's not really surprising. Had ZMA actually increased free test levels upwards of 30%, we'd all be packing on lean muscle like we had D-bol flowing through our veins, and that just doesn't happen. Interesting on the elevated serum zinc levels, though. No mention of Mg, which is too bad. Thanks to TX911 for throwing this my way.
Acta Physiol Hung. 2006 Jun;93(2-3):137-44.
Links
The effect of magnesium supplementation on lactate levels of sportsmen and sedanter.
Cinar V,
Nizamlioğlu M,
Moğulkoc R.
High School of Physical Education and Sport of Karaman, Selcuk University, Karaman, Turkey.
cinarvedat@hotmail.com
This study was performed to assess how magnesium supplementation affects plasma lactate levels at rest and exhaustion in sportsmen and sedentary. Research was performed on 30 healthy subjects varying between 18-22 years of age for a four-week period. Subjects were separated into 3 groups: Group 1; sedentary taking magnesium supplementation only (10 mg/kg/day) (Mg + S), Group 2; subjects magnesium supplemented + training 90-120 min 5 days a week (Mg + Training), Group 3; training 90-120 min 5 days a week. Lactate levels of the groups were measured 4 times; at rest and exhaustion in the beginning of the research and after the end of the research. At the end of the research, exhaustion measurements both before and after supplement were found significantly higher than rest measurements in terms of lactate levels (p < 0.05). An important decrease was determined in the lactate levels of the 1st and 2nd groups when compared to their first measurements (p < 0.05). The results of this research indicate that lactate increases with exhaustion.
However, magnesium supplement may positively affect performance of sportsmen by decreasing their lactate levels.
Woo, chalk up one for Mg. Perhaps an effective buffer?
Biol Trace Elem Res. 2007 Mar;115(3):205-12.
Links
Effects of magnesium supplementation on blood parameters of athletes at rest and after exercise.
Cinar V,
Nizamlioglu M,
Mogulkoc R,
Baltaci AK.
High School of Physical Education and Sport, Selcuk University, Karaman, Turkey.
The effects of magnesium supplementation on blood parameters were studied during a period of 4 wk in adult tae-kwon-do athletes at rest and exhaustion. Thirty healthy subjects of ages ranging in age from 18 to 22 yr were included in the study. The subjects were separated into three groups, as follows: Group 1 consisted of subjects who did not train receiving 10 mg/kg/d magnesium. Group 2 included subjects equally supplemented with magnesium and exercising 90-120 min/d for 5 d/wk. Group 3 were subject to the same exercise regime but did not receive magnesium supplements. The leukocyte count (WBC) was significantly higher in groups 1 and 2 than in the subjects who did not receive any supplements (p < 0.05). There were no significant differences in the WBC of the two groups under magnesium supplementation. The erythrocyte, hemoglobin, and trombocyte levels were significantly increased in all groups (p < 0.05), but the hematocrit levels did not show any differences between the groups although they were increased after supplementation and exercise.
These results suggest that magnesium supplementation positively influences the performance of training athletes by increasing erythrocyte and hemoglobin levels.
Well, increasing hemoglobin is always a good thing; just ask any Tour de France competitor. 
Another one for Mg.