The Effects of the Female Reproductive Cycle on Metabolic Rate - Assignment Example

? Metabolic rate in females, unlike males does not remain constant and shows a consistent pattern of variation corresponding to phases of reproductive cycle. The female reproductive cycle is characterised by changes in hormonal levels, energy balance and other associated changes which are responsible for changes in the metabolic rate, although the underlying mechanism of these changes is still not well understood. The alterations in the energy balance as a consequence of reproductive cycle changes have also been studied in correlation with extra energy requirements of the body during and after intense physical activity such as exercise. The present study was undertaken to study the variations in BMR in different phases of reproductive cycle, during rest, exercise and post exercise recovery phases in six female subjects. BMR was calculated on the basis of respiratory quotient (RQ) using respiratory gas analysis. Large intra and inter subject variations were reported in BMR values, and a constant peak was observed for ovulation phase. Results Mean+- standard deviance for o2 and co2 consumption at rest, . A) O2 consumption at rest Week 1 Week 2 Week 3 Week 4 Mean 19.33 18.88 18.87 19.17 Standard deviation 0.81 0.81 0.53 0.73 B) Co2 consumption at rest Week 1 Week 2 Week 3 Week 4 Mean 1.92 2.02 2.45 2.15 Standard deviation 0.57 0.48 0.52 0.30 C) Total volume expired Week 1 Week 2 week 3 Week 4 Mean 47.68 58.20 52.12 58.53 Standard deviation 26.98 16.18 16.77 21.57 FIGURE 11: shows the overall mean and standard deviance of O2, Co2 and Total volume expired at rest. A)Exercise A) B) C) Figure 12: shows the overall mean and standard deviance of O2, Co2 and Total volume expired during exercise. Recovery phase: o2 Week 1 Week 2 week 3 Week 4 Mean 18.90 18.67 18.98 16.38 Standard deviation 0.41 0.29 0.37 6.38 Week 1 Week 2 week 3 Week 4 Mean 2.27 2.57 2.43 2.57 Standard deviation 0.43 0.74 0.57 0.61 Figure 13: shows the overall mean and standard deviance of O2, Co2 and Total volume expired during recovery. Figure 14: Comparison of all values at rest for o2 and co2 with t-test. a) rest o2   Subjects week 1 week 2 1 19 18.9 2 19 19 3 19.5 19.6 4 20.8 17.9 5 19.3 18 6 18.4 19.9       T-TEST 0.49               rest o2   Subjects week 1 week 3 1 19 18.5 2 19 18.8 3 19.5 19.5 4 20.8 18.9 5 19.3 19.4 6 18.4 18.1       T-TEST 0.18               rest o2   Subjects week 1 week 4 1 19 18.1 2 19 18.8 3 19.5 18.9 4 20.8 19.8 5 19.3 20.1 6 18.4 19.3       T-TEST 0.65   b) rest o2   Subjects week 2 week 3 1 18.9 18.5 2 19 18.8 3 19.6 19.5 4 17.9 18.9 5 18 19.4 6 19.9 18.1       T-TEST 0.97               rest o2   Subjects week 2 week 4 1 18.9 18.1 2 19 18.8 3 19.6 18.9 4 17.9 19.8 5 18 20.1 6 19.9 19.3       T-TEST 0.63               rest o2   Subjects week 3 week 4 1 18.5 18.1 2 18.8 18.8 3 19.5 18.9 4 18.9 19.8 5 19.4 20.1 6 18.1 19.3       T-TEST 0.36   c) rest co2   Subjects week 1 week 2 1 1.6 1.8 2 2.2 2.3 3 1.6 1.2 4 1.2 2.6 5 2.1 2.2 6 2.8 2       T-TEST 0.75               rest co2   Subjects week 1 week 3 1 1.6 2.4 2 2.2 2.9 3 1.6 1.6 4 1.2 2.3 5 2.1 2.4 6 2.8 3.1       T-TEST 0.02               rest co2   Subjects week 1 week 4 1 1.6 2.5 2 2.2 2.3 3 1.6 1.8 4 1.2 1.8 5 2.1 2.1 6 2.8 2.4       T-TEST 0.27   d) rest c02   Subjects week 2 week 3 1 1.8 2.4 2 2.3 2.9 3 1.2 1.6 4 2.6 2.3 5 2.2 2.4 6 2 3.1       T-TEST 0.07               rest co2   Subjects week 2 week 4 1 1.8 2.5 2 2.3 2.3 3 1.2 1.8 4 2.6 1.8 5 2.2 2.1 6 2 2.4       T-TEST 0.58               rest co2   Subjects week 3 week 4 1 2.4 2.5 2 2.9 2.3 3 1.6 1.8 4 2.3 1.8 5 2.4 2.1 6 3.1 2.4       T-TEST 0.11   Figure 15: Exercise phase comparison of each week. O2 and co2 & t-test a) b) exercise o2   subject week 2 week 3 1 17.6 17.6 2 17.2 17.1 3 18.7 18.6 4 18.1 17.8 5 17.9 18.2 6 19.1 17       T-TEST 0.33               exercise o2   subject week 2 week 4 1 17.6 17.1 2 17.2 16.9 3 18.7 18.2 4 18.1 18 5 17.9 18.7 6 19.1 17.4       T-TEST 0.30               exercise o2   subject week 3 week 4   17.6 17.1   17.1 16.9   18.6 18.2   17.8 18   18.2 18.7   17 17.4       T-TEST 1.00   c) exercise Co2   subjects week 1 2 1 2.7 3 2 2.6 3.6 3 3.2 2.6 4 4.1 3.7 5 3.1 3.9 6 2.7 4.4       T-TEST 0.25               exercise Co2   subjects week 1 week 3 1 2.7 3.5 2 2.6 3.9 3 3.2 2.4 4 4.1 3.7 5 3.1 3.9 6 2.7 4.6       T-TEST 0.21               exercise Co2   subjects week 1 week 4 1 2.7 3.8 2 2.6 3.5 3 3.2 2.8 4 4.1 3.6 5 3.1 3.8 6 2.7 4.9       T-TEST 0.17   d) exercise co2   subjects 2 week 3 1 3 3.5 2 3.6 3.9 3 2.6 2.4 4 3.7 3.7 5 3.9 3.9 6 4.4 4.6       T-TEST 0.25               exercise Co2   subjects week 2 week 4 1 3 3.8 2 3.6 3.5 3 2.6 2.8 4 3.7 3.6 5 3.9 3.8 6 4.4 4.9       T-TEST 0.25               exercise o2   subjects week 3 week 4 1 3.5 3.8 2 3.9 3.5 3 2.4 2.8 4 3.7 3.6 5 3.9 3.8 6 4.6 4.9       T-TEST 0.63   Figure 16: Recovery phase comparison of each week. O2 and co2 & t-test a) recovery O2   subjects WEEK1 WEEK 2 1 19.2 19 2 19.3 18.8 3 19.3 18.6 4 18.7 18.2 5 18.4 18.9 6 18.5 18.5       T-TEST 0.25               recovery O2   subjects WEEK 1 WEEK 3 1 19.2 19 2 19.3 18.7 3 19.3 19.5 4 18.7 19.3 5 18.4 18.9 6 18.5 18.5       t-test 0.67               recovery O2   subjects WEEK 1 WEEK 4 1 19.2 18.3 2 19.3 18.8 3 19.3 19.2 4 18.7 19.7 5 18.4 3.4 6 18.5 18.9       T-TEST 0.36   b) recovery O2   subjects WEEK 2 WEEK 3 1 19 19 2 18.8 18.7 3 18.6 19.5 4 18.2 19.3 5 18.9 18.9 6 18.5 18.5       T-TEST 0.21               recovery O2   subjects WEEK 2 WEEK 4 1 19 18.3 2 18.8 18.8 3 18.6 19.2 4 18.2 19.7 5 18.9 3.4 6 18.5 18.9       T-TEST 0.43               recovery O2   subjects week 3 week 4 1 19 18.3 2 18.7 18.8 3 19.5 19.2 4 19.3 19.7 5 18.9 3.4 6 18.5 18.9       T-TEST 0.36   c) recovery CO 2   subjects WEEK 1 WEEK 2 1 1.6 1.8 2 2.5 2.7 3 2.1 1.7 4 2.2 18.7 5 2.3 2.8 6 2.9 3.7       T-TEST 0.32               recovery CO 2   subjects WEEK 1 WEEK 3 1 1.6 2.3 2 2.5 2.9 3 2.1 1.6 4 2.2 2 5 2.3 2.7 6 2.9 3.1       T-TEST 0.40               recovery CO 2   subjects WEEK 1 WEEK 4 1 1.6 2.4 2 2.5 2.8 3 2.1 1.8 4 2.2 2 5 2.3 3.4 6 2.9 3       T-TEST 0.24   d) recovery CO 2   subjects WEEK 2 WEEK 3 1 1.8 2.3 2 2.7 2.9 3 1.7 1.6 4 18.7 2 5 2.8 2.7 6 3.7 3.1       T-TEST 0.36               recovery CO 2   subjects WEEK 2 WEEK 4 1 1.8 2.4 2 2.7 2.8 3 1.7 1.8 4 18.7 2 5 2.8 3.4 6 3.7 3       T-TEST 0.39               recovery CO 2   subjects WEEK 3 WEEK 4 1 2.3 2.4 2 2.9 2.8 3 1.6 1.8 4 2 2 5 2.7 3.4 6 3.1 3       T-TEST 0.33   Figure 17:Total volume expired at rest: a) rest total volume expired Subjects week 1 2 1 21 59 2 39 57.2 3 52.9 59 4 44.8 42.3 5 97.9 87.5 6 30.5 44.2       T-TEST 0.19               rest total volume expired Subjects week 1 week 3 1 21 37.2 2 39 66.7 3 52.9 70.5 4 44.8 39.2 5 97.9 64.6 6 30.5 34.5       T-TEST 0.64               rest total volume expired Subjects week 1 week 4 1 21 31.3 2 39 80.4 3 52.9 53.5 4 44.8 55.5 5 97.9 87.4 6 30.5 43.1       T-TEST 0.19   b) rest total volume expired Subjects week 2 week 3 1 59 37.2 2 57.2 66.7 3 59 70.5 4 42.3 39.2 5 87.5 64.6 6 44.2 34.5       T-TEST 0.36               rest total volume expired subjects week 2 week 4 1 59 31.3 2 57.2 80.4 3 59 53.5 4 42.3 55.5 5 87.5 87.4 6 44.2 43.1       T-TEST 0.96               rest total volume expired subjects week 3 week 4 1 37.2 31.3 2 66.7 80.4 3 70.5 53.5 4 39.2 55.5 5 64.6 87.4 6 34.5 43.1       T-TEST 0.34   a) exercise total volume expired subjects week 1 week 2 1 38 93.2 2 119.2 111.3 3 60.2 93.2 4 90.9 118.8 5 145.3 147.7 6 99.5 100.5       T-TEST 0.12               exercise total volume expired subjects week 1 week 3 1 38 86 2 119.2 116 3 60.2 80.4 4 90.9 101.2 5 145.3 129.4 6 99.5 96.3       T-TEST 0.36               exercise total volume expired   subjects week 1 week 4 1 38 100 2 119.2 98.3 3 60.2 103.2 4 90.9 135.1 5 145.3 138.3 6 99.5 106.8       T-TEST 0.17   b) exercise total volume expired   subjects week 2 week 3 1 93.2 86 2 111.3 116 3 93.2 80.4 4 118.8 101.2 5 147.7 129.4 6 100.5 96.3       T-TEST 0.05               exercise total volume expired   subjects week 2 4 1 93.2 100 2 111.3 98.3 3 93.2 103.2 4 118.8 135.1 5 147.7 138.3 6 100.5 106.8       T-TEST 0.57               exercise total volume expired   subjects 3 4 1 86 100 2 116 98.3 3 80.4 103.2 4 101.2 135.1 5 129.4 138.3 6 96.3 106.8       T-TEST 0.15   Table 1: Calculated Metabolic Rates and efficiency (week 1) Subject 1 (Follicular Phase) Subject 2 (menstrual phase) Subject 3 (menstrual phase) Subject 4 (Follicular Phase) Subject 5 (Follicular Phase) Subject 6 (menstrual phase) BSA (m2) 1.67 1.97 1.46 1.72 1.66 1.99 Resting MR (J min-1) 2478.36 4833.10 4809.01 955.186 10549.64 4936.884 Exercising MR (J min-1) 6192.68 22778.22 11417.53 7650.17 23.778.47 16215.04 Recovery MR (J min-1) 5192.35 6699.95 6487.11 5422.78 16290.87 7363.057 Power output (w) 20 26 22 29 21 27 Efficiency (%) 32.31 8.69 19.97 25.99 9.52 14.36 Table 2: Calculated Metabolic Rates and efficiency (week 2) Subject 1 (Ovulation Phase) Subject 2 (Follicular Phase) Subject 3 (Follicular Phase) Subject 4 (Ovulation Phase) Subject 5 (Ovulation Phase) Subject 6 (Follicular Phase) BSA (m2) 1.67 1.97 1.46 1.72 1.66 1.99 Resting MR (J min-1) 7418.77 7311.82 4889.98 7875.03 15368.71 3506.41 Exercising MR (J min-1) 19249.76 26115.32 13681.67 22779.59 30188.98 15310.66 Recovery MR (J min-1) 9194.44 9530.63 10395.46 19729.43 10225.69 7223.23 Power output (w) 22 24 22 27 21 28 Efficiency (%) 11.16 7.66 15.01 10.87 8.50 14.23 Table 3: Calculated Metabolic Rates and efficiency (week 3) Subject 1 (luteal phase) Subject 2 (Ovulation Phase) Subject 3 (Ovulation Phase) Subject 4 (luteal phase) Subject 5 (luteal phase) Subject 6 (Ovulation Phase) BSA (m2) 1.67 1.97 1.46 1.72 1.66 1.99 Resting MR (J min-1) 5722.79 9743.73 6585.37 5203.83 7076.61 6325.12 Exercising MR (J min-1) 18365.41 28276.83 11972.93 20899 24538.05 24893.51 Recovery MR (J min-1) 6621.56 8509.18 7308.96 4764.82 8287.21 6768.25 Power output (w) 22 23 20 26 23 29 Efficiency (%) 10.44 7.45 22.27 9.94 7.90 9.37 Table 4: Calculated Metabolic Rates and efficiency (week 4) Subject 1 (menstrual phase) Subject 2 (luteal phase) Subject 3 (luteal phase) Subject 4 (menstrual phase) Subject 5 (menstrual phase) Subject 6 (luteal phase) BSA (m2) 1.67 1.97 1.46 1.72 1.66 1.99 Resting MR (J min-1) 5493.75 11106.37 6745.00 4535.72 6216.74 4950.23 Exercising MR (J min-1) 24236.4 24378.57 17978.57 26380.59 22628.68 25954.43 Recovery MR (J min-1) 7496.61 10123.15 11194.67 3406.19 88215.22 5574.43 Power output (w) 20 24 24 27 22 28 Efficiency (%) 6.40 10.85 12.82 7.42 8.04 8.0 Discussion Metabolic energy is imperative for performance of body functions and maintaining body temperature within the narrow range of 97-99.5.F. Besides the BMR some other external and internal conditions affect body temperatures. In women, reproductive cycle is a major factor affecting the body temperature, with body temperatures rising approximately 0.5 degrees after ovulation. Hormonal changes associated with the reproductive cycle have therefore been studied for their impact on metabolic rate and vice versa. In the preset study both individual and temporal variations were observed in the study with respect to phases of reproductive cycle as well as during rest, exercise and recovery phases. One of the major indicators of the energy utilization of biological system is respiratory quotient, which is determined on the basis of oxygen uptake and carbon dioxide excreted by the body. The study involved the measurements of oxygen taken up by the subjects during rest, exercise and recovery phases during the four weeks of study. A t-test of the amounts of oxygen taken up by the subjects revealed significant differences during the week 2 and week 3. The amount of carbon dioxide excreted differed maximum in the week 1 and 2. RQ is indicative of the metabolic rates of the body as well as the type of nutrient being metabolised, an RQ equal to 1 being indicative of carbohydrate utilization and a value below 1 indicative of other sources of energy, specifically fat being utilised. The RQ was found to decrease in the week 2 for all subjects except subject 1. The fall was more pronounced for studies during and post exercise phase. The results are thus indicative of a higher demand for energy during week two and during the exercise and recovery phases for most subjects. Menstrual cycle is a biphasic cycle with respect to body temperatures, with temperatures rising during the post ovulation phase and dipping during the pre menstrual phase. Correspondingly metabolic rate is expected to be maximum during the ovulation phase and lowest during the premenstrual phase. During the present study data was collected simultaneously from the six subjects irrespective of the synchronicity in the phases of their menstrual cycles, however records were maintained as to the phase of the reproductive cycle corresponding to the week of data collection for individual subjects. Peak values of BMR are observed for each subject during the ovulation phase with a more pronounced rise reported for data collected during exercise. The luteal phase dip is not prominent in the study conducted, though it is reported in subject 6. However the inconsistency of the data in this regard makes it unsuitable for drawing generalisations. The study shows high levels of inter and intra subject variations in BMR with respect to the phases of reproductive cycle. Changes in metabolic rate corresponding to the changes in level of activity of the body have been well understood and documented. However the effect of menstrual cycle in conjunction with exercise or even alone is not well understood. It has been speculated that changes in BMR during menstrual cycle can be a consequence of changes in levels of hormone progestin (P). Levels of P have been reported to rise during the luteal phase, and are known to exhibit a postmenstrual fall (29). Estrogens too have been implicated in BMR variations corresponding to the phases of menstrual cycle, but evidences are insufficient to be certain of their role as well. The mechanisms underlying the changes in body temperatures associated with phases of reproductive cycle are not understood, but the fact that BMR does differ with respect to the phase of reproductive cycle is well proven. Previous researches have reported varied results with respect to changes in BMR as a consequence of reproductive cycle phases. While some have reported wide variations, others have failed to report any significant changes. The lack of consensus can be due to variations in the methods of data collection or as in the present study can be attributed to individual variations. Hormone levels although not monitored as a part of present study are the major factors contributing to BMR changes during various phases of reproductive cycle. Progesterone is known to be a hyperthermic hormone. The secretion of this hormone leads to an elevation of body temperatures. It is reported to stimulate the metabolic activity and is responsible for higher energy expenditure during the post ovulatory phase. It has been reported that the levels of progesterone rises before the ovulation phase, reaching a peak during ovulation and dips during the luteal phase. A similar pattern in the rise and fall BMR is also recorded. One of the major impacts of progesterone and its metabolism stimulating activity is observed in form of increased diet of women with difference as high as 500kcal/day compared to days preceding ovulation. Estrogen level on the other hand, reaches its peak value during the post ovulatory period, with a second smaller peak during premenstrual period. None of these correspond to the pattern of BMR variations and hence most studies have rejected the role of estrogen in BMR changes associated with reproductive cycle (Soloman et al., 1982). The patterns of changes in BMR, even though minor have important implications in terms of energy balance. Corresponding to the biphasic changes in BMR, the energy efficiency and energy balance too undergo a biphasic change. A 9% rise in energy expenditure has been reported for luteal phase of reproductive cycle, compared to the follicular phase (Webb, 1986). Women are in a positive energy balance during the luteal phase of their reproductive cycle and conversely in a negative energy balance during the follicular phase. This variations in energy are important with respect to elevated levels of physical activity, such as during a sports activity or exercise. Moreover if as a consequence of administration of oral contraceptives, the ovulation is stopped, the extra energy expenditure associated with this phase is also restricted. This can lead to slower rise of body fat in women not undergoing ovulation due to contraceptives or as a consequence of menopause. In fact women taking oral contraceptives have been reported to have similar BMR values during the month, irrespective of the reproductive cycle (Bisdee et al., 1989). The small sample size forms the major limitation of the study. Besides this certain uncontrolled factors such as subjects undergoing different phases of reproductive cycle during the weeks of study too could have lead to the inconsistencies in the test results. However, since we aimed to study the variations in BMR with respect to the natural cycle, this factor could not be controlled. A larger sample size and data on other contributing factors such as levels of hormones during the various phases of cycle can provide better results and also help provide information on the etiology of BMR variations. The study can be very helpful for training of female sportspersons and even other women who remain physically active as a part of their profession or lifestyle. Variations in BMR can be used to study the diet pattern and effects of calorie intake on women with natural active reproductive cycle, women taking oral contraception and post menopausal women. References 1. Bisdee, J. T., James, W. P., & Shaw, M. A. (1989). Changes in energy expenditure during the menstrual cycle. British Journal of nutrition , 187-99. 2. Soloman, S. J., Kurzer, M. S., & Calloway, D. H. (1982). Menstrual cycle and basal metabolic rate in women. Am J Clin , 611-6. 3. Webb, P. (1986). 24 hour energy expenditure and the menstrual cycle. Am J Clin Nutr, 614-9. Read More