Twenty-two females and 10 males completed all four of the self-reported dietary assessments. Subjects who reported the consumption of multivitamins submitted product labels with the dietary assessments. Supplement nutritional data were derived from the labels and included with the nutritional intake data. Mean values for total, heme, and bioavailable iron intakes are presented in Table 4. A significant main effect of time was observed for total iron intake with no significant gender interaction. Heme and bioavailable iron intakes did not significantly change over time. Significant gender main effects were observed for total and heme iron intake values (P < 0.05). Marginal means for the female and male groups were 11.3 ± 0.9 and 14.6 ± 1.3 mg·d−1 for total iron and 0.9 ± 0.1 and 1.3 ± 0.1 mg·d−1 for heme iron, respectively. Dietary iron intakes were not significantly correlated with any of the blood chemistry measures. No significant differences or interactions were observed for dietary iron intake values between subjects participating in the summer and fall training programs.
The SF level of the male group in the current investigation was significantly lowered (22%) from baseline (85.8 vs 66.9 μg·L−1) during the course of the weight training program. A 34% drop in the SF level after 6 wk (74.8 vs 49.3 μg·L−1) (22) and a 28% drop after 8 wk (83.0 vs 60.0 μg·L−1) (13) of training have been reported. Despite the adverse effects that weight training may exert on the iron status of young males, an important point to make is that SF levels have remained within the normal range (13,22). However, because the SF level is a positive acute phase protein, levels within the range of 50–100 μg·L−1 may still be indicative of iron deficiency (2). Upon further analysis, it was observed that only males in the MN group experienced a significant (21.5%) decrease in SF levels at week 9. Lack of a significant change in the SF level of the ML group was likely due to low iron stores among these individuals. The observed changes in the SF level of the MN group were not observed among the females in the FN group. However, despite being classified with normal iron status, females in the FN group possessed low serum ferritin levels. Lack of a significant change in the SF level of the female subjects in the present investigation conflicts with previous reports. Significant decreases (19) and increases (14) in SF levels were observed in older and younger women after 12 wk of weight-training exercise, respectively. A combination of age (19) and differences in exercise program design (14,19) are two factors that may explain the observed differences in SF level between investigations. The older women in the study of Murray-Kolb et al. (19) possessed an initial SF level of 123.1 μg·L−1, which is much higher than the mean values of the FL (7.3 μg·L−1) and FN (41.7 μg·L−1) groups in the present study. Also, the females in previous studies trained only twice per week (14,19) and/or participated in a less rigorous, “aerobic-resistance” exercise protocol (14).
Serum iron levels, TIBC, and TS did not demonstrate significant changes as a result of the weight-training program. The lack of change in measures of iron transport is in agreement with results of Schobersberger et al. (22), who did not observe changes in SI or TS among young males undergoing 6 wk of weight training. However, these data are in contrast to those of Lukaski et al. (13), who observed an increased TIBC (P < 0.05) and decreased TS (P < 0.05), suggesting impaired iron transport. Although significant alterations in iron transport were found in the study, values were still within the normal range.
Total iron intake, but not heme or bioavailable iron intakes, decreased significantly at week 13 compared with weeks 1, 5, and 9. Lukaski et al. (13) also reported a significant decline in iron intake among a group of young males participating in an 8-wk weight-training program (23 mg·d−1 pre vs 19.3 mg·d−1 post). The decline in iron intake at week 13 corresponds with the observed decrease in hemoglobin levels; however, none of the dietary iron intake measures were significantly correlated with hemoglobin levels. Additionally, lack of a significant change in bioavailable iron intake suggests that iron absorption did not increase, nor did iron absorption contribute to the observed decline in hemoglobin levels.
To date, only one paper has examined the effect of long-term weight-training exercise (12 wk) on the sTfR level (19). An increased FFM (2.1 kg) was hypothesized to be the reason for the increased sTfR level observed among a group of older males (19). In the present study, however, no difference in the sTfR level was observed despite a significantly increased FFM of 1.4 and 0.9 kg for the males and females, respectively. It is possible that the increased levels of FFM observed among the males and females in the present investigation was not sufficient to produce a measurable difference in sTfR levels. Due to the inverse regulation of the sTfR and SF measures, it has been suggested that a ratio of the two parameters provides a sensitive measure of tissue iron deficiency (25). Murray-Kolb et al. (19) observed an increase in the sTfR:ferritin ratio after 12 wk of weight training among older males and females; however, such a change was not observed in the current investigation. Failure to observe a dramatic increase in circulating levels of CK may be explained by blood sample timing and the protective effect of repeated bouts of exercise on skeletal muscle. It is possible that large elevations in CK occurred in the days after the blood sampling periods. Significant elevations in CK have been typically observed 3–5 d after maximal eccentric exercise involving small muscle groups (20). Peak CK values have been observed after 4–5 d after weight-training exercise among untrained males (27). In the current study, the second blood sample (week 5) was obtained after 4 wk of weight-training exercise; in which time a training effect may have occurred (16). Therefore, it remains a possibility that the nonsignificant change in CK measured at weeks 5, 9, and 13 were due to adaptation of the skeletal muscle to prior bouts of weight-training exercise (16,27). Additionally, failure to observe an increase in SF level (5) and lack of significantly lower SI, TS, and TIBC levels (9) are evidence against the occurrence of an exercise-induced acute phase response.
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