542
Response of Beta-Endorphin and Estradiol to Resistance Exercise in Females during Energy Balance and Energy Restriction .1 Walberg-Rankin, W D. Franke, F C. Gwazdauskas Division of Health and Physical Education, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
Introduction
Abstract
Energy Restriction. mt j Sports Med, Vol 13, No 7, pp 542— 547, 1992.
Accepted: July 14, 1992 The acute effect of weightlifting on beta-en-
dorphin and estradiol was studied in experienced female recreational weightlifters. Five eumenorrheic females completed two months of testing, each with a different sequence of testing conditions (SEQ 1 and SEQ2). In SEQ1, a week of weight maintenance diet and prescribed exercise
(3d wk-1, 3 sets, ''85 % I RM, 10—12 reps, eight lifts) beginning on d 11 of their menstrual cycle was followed by measurement of hormone response to a weightlifting bout during energy balance (EBAL) on d 18. This included blood sampling via a catheter before, just after, and at 15 and 30 mm of recovery. The women consumed 500 kcal per day for
the next 48 hrs and then repeated the weight!ifting test during negative energy balance (NEBAL). SEQ2 was similar
except that the 48 hrs of NEBAL preceded the EBAL test condition. Estradiol and beta-endorphin increased from baseline to immediately post exercise under both dietary
conditions but was significant only during NEBAL.
Female endurance athletes have repeatedly been observed to have a higher incidence of menstrual dysfunction than nonathletes (15). Data from our laboratory (29) indicate that menstrual disruption is also more common in weightlifters than non-weightlifters. Thirty percent of a group of rec-
reational weightlifters reported either oligomenorrhea or amenorrhea as compared to 13 % of non-weightlifters. Although low body fat has been suggested as a cause for a change
in cyclicity of athletes, the recreational weightlifters were of normal body fat which was similar to that of the control group. Thus, other factors must be involved in this abnormal prevalence of oligomenorrhea. Repeated acute hormonal changes associated with exercise have been suggested as a mechanism for menstrual alterations (3). For example, an increase in estradiol is known to cause a negative feedback effect on the hypothalamus to reduce gonadotropin releasing hormone (GnRH). Thus, repeated increases in this hormone could contribute to reduced stimulation of gonadotropin release from the pituitary Several studies have reported that aerobic exercise increased blood
estradiol concentration (3, 13). This hormone has not been measured with exercise which included significant anaerobic metabolism such as resistance training.
Another hormone that has been implicated in hypothalamic control of GnR}1 release is beta-endorphin
Estradiol increased 1.6 fold and beta-endorphin 3.7 fold by the end of the resistance exercise bout during NEBAL. Both hormones were also elevated for a longer time during re-
(BEND). Several recent reviews have focused on the role that this hormone may have in female reproductive dysfunction (8,
covery in the NEBAL condition. Since estradiol and beta-endorphin can suppress gonadotropin release, it is possible that repeated elevations in these hormones during weightlifting, especially concurrent with energy restriction, could contribute to disruption of the menstrual cycle.
reduced LH pulsatility (11). Thus, increases in estradiol and/or beta-endorphin could contribute to changes in GnRH release and thus menstrual cyclicity.
Key words _______________________________ Resistance exercise, beta-endorphin, estradiol, exercise, menstrual function ____________________________________________
21, 23). For example, infusion of BEND in men caused a decrease in LH (20) and injection of morphine in monkeys
Aerobic exercise has been shown to increase blood BEND concentration (25). High intensity exercise appears to be important in eliciting this hormonal response. Although resistance exercise is very intense, one study examining
the BEND response to resistance exercise, using repeated isometric contractions, did not find any increase in BEND (18). Cumming et a!. (7), however, reported increases in several other hormones associated with the reproductive cycle such as LH, FSH and testosterone in women following a weightlifting session.
mt. J. Sports Med. 13 (1992) 542—547 Georg Thieme Verlag Stuttgart New York
Weight loss appears to increase the risk of menstrual disruption. Bullen et al. (5) reported that runners who
Downloaded by: Queen's University. Copyrighted material.
.1 Walberg-Rankin, W D. Franke and F C. Gwazdauskas, Response of Beta-Endorphin and Estradiol to Resistance Exercise in Females during Energy Balance and
mt. .1 Sports Med. 13 (1992) 543
Response of Beta-Endorphin and Estradiol to Resistance Exercise in Females
ners who maintained their weight during training. This could be mediated through hormonal changes induced by energy restriction which influence gonadotropin release. For example, Dyer Ct al. (9) determined that the reduction in the magnitude of LH
pulsatility in rats undergoing an acute fast was mediated by opioid inhibition in the brain.
As reported earlier by this laboratory (29), women participating in regular resistance training had excessive concern relative to inactive women about their body weight and food consumption. Female weightlifters who compete in body
building competitions typically undergo repeated caloric restriction to achieve the extremely lean physique that is required for this sport. This negative energy balance may contribute to the increased menstrual disruption seen in this population.
This study was designed to examine several questions concerning female weightlifters. First, what is the acute effect of a typical weightlifting bout on BEND and estradiol? Secondly, is the effect of weightlifting on these hormones altered by a negative energy balance? Answers to these questions may help to explain the increased frequency of menstrual disturbance observed previously in female weightlifters.
Methods
Subjects and Design Five females involved in recreational weightlifting were recruited from a University campus weight club. The study was approved by the Institutional Review Board for Research Involving Human Subjects. All subjects were informed of risks and signed informed consents. None reported to be on birth control pills or anabolic steroids and all reported normal menstrual cycles of average length at consistent intervals. Our purpose was to recruit women who were experienced in resistance training and those who were past the initial phase of adaptation when beginning a resistance exercise program. Thus, all subjects were currently weightlifting at least three days per week (up to seven days per week) for from 30 minutes to 2 hours per session for the purpose of physique development.
They had been regularly lifting with this schedule for a minimum of 4 months and up to 5 years. Descriptive information on the subjects is supplied in Table 1.
day of cycle: 9 10 11 12 13 14 15 16 17 18 19 20 21 seq 1
oo&oôcooaoôooooooOo
seq 2
= energy maintenance
diet
A = blood sampling
+
A
A
A
A
= energy restriction wt. lifting bout
Fig. I Experimental design.
All women were asked to participate in two months of testing (Fig. 1). Each month included two tests of the acute hormonal response to weightlifting, one in energy balance
(EBAL) and one in negative energy balance (NEBAL). The order of the EBAL and NEBAL tests were changed for the two
months so that possible influence of sequence of treatment could be evaluated. Thus, one month the individual performed
the experiment in sequence 1 (SEQ1) where EBAL test preceded the NEBAIL test. Sequence 2 (SEQ2), when the order was reversed, was performed the other month. The initial assignment to SEQ 1 or SEQ2 was random.
Each month the women followed a baseline week, consisting of a prescribed weight maintenance diet of similar composition (30 keal /kg, adjusted as needed to maintain body weight, 15 % protein, 30% fat, 55 % carbohydrate) using the diabetic exchange system (1) and a similar weight training program for one week. This maintenance week began on day ii (defined as the 11th day after the start of menses) during SEQ1 and day 9 during SEQ2.
At the end of the maintenance week (d 18 for SEQ1 and d 16 for SEQ2), all women had their body composition assessed using skinfold measurement. Then, those in SEQ1 underwent a test of acute hormonal response to a weightlifting bout. This test included insertion of a catheter into a forearm vein which was kept patent with a heparin lock. After supine resting for 45 minutes the first 5 ml blood sample was withdrawn (time —60) and was considered a baseline sample. Immediately following that sampling, the subjects participated in a weightlifting session (catheter in place) of approximately one hour in duration. A second blood sample was withdrawn at the end of the exercise bout (time 0), another after 15 minutes of
recoveiy (time 15), and the last sample at 30 minutes of recovery (time 30). Subjects were seated throughout the recovery period.
Table I Subject characteristics and initial strength (1 RM) measurements. Age (yrs) Height (cm) Bodyweight (kg)
% Body Fat Bench press* (kg) Abdominal crunch (kg) Cable rows (kg) Seated press (kg) Lat pulls (kg) Leg extension (kg) Leg curls (kg) Squats (kg)
24.4 2.0 169.8 1.8 62.1
23.7 39.7 6.6 49.5
6.1
50.4 5.6 27.8 4.2 47.6 6.0
64.3 5.1 35.3
2.5
52.7 ±6.0
Values are averages SEM for five subjects. *1 RM values were estimated from tests of 5 RM.
Subjects in SEQ1 were then given a formula hypocaloric diet to consume for the next 48 hrs. No exercise
was to be done during this time period. Then, on d20 the hormonal response to weightlifting protocol was repeated.
In SEQ2, the women were prescribed the weight maintenance diet for d 9 through 15 and then given the formula hypocalonc diet to consume for 48 hrs (d 16 and 17) prior to the hormonal response to weightlifting protocol. Then,
the women consumed the diabetic exchange, maintenance energy diet for 48 hours prior to repeating the hormonal response test (d20).
Time of blood sampling during the acute weightlifting test varied between women between 10:00 am and
3:00pm depending on subjects' availability for this two hour
Downloaded by: Queen's University. Copyrighted material.
were losing weight had more menstrual dysfunction than run-
544 Int. I Sports Med. 13 (1992)
.1 Walberg-Rankin, W D. Franke, E C. Gwazdauskas
block of time but was maintained the same for both sequences in each individual subject.
Statistical procedures The hormonal response to exercise was ana-
(SEQ 1). Thus, there was a total of 9 acute weightlifting tests during EBAL and 9 during NEBAL.
Hypocaloric diet
The hypocaloric diet consisted of 2 cans of Ensure (Ross Laboratories; 250 kcai, 9.3 g protein, 8.8 g fat, 33.8 g carbohydrate per can) per day. All subjects were encouraged to drink 1 liter of water per day.
lyzed in several ways. The absolute hormone concentration for both treatments (EBAL and NEBAL) was compared over time
at the four time points using repeated measures ANOVA. In addition, the total area under the curve was computed for each hormonal response. A possible effect of sequence of treatment was tested by computing the residual effect of sequence. This repeated measures ANOVA takes both the between-subject and within-subject variance into account. Differences between individual means were assessed using a Tukey post hoc test. A p-value of
Response of Beta-Endorphin and Estradiol to Resistance Exercise in Females during Energy Balance and Energy Restriction .1 Walberg-Rankin, W D. Franke, F C. Gwazdauskas Division of Health and Physical Education, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
Introduction
Abstract
Energy Restriction. mt j Sports Med, Vol 13, No 7, pp 542— 547, 1992.
Accepted: July 14, 1992 The acute effect of weightlifting on beta-en-
dorphin and estradiol was studied in experienced female recreational weightlifters. Five eumenorrheic females completed two months of testing, each with a different sequence of testing conditions (SEQ 1 and SEQ2). In SEQ1, a week of weight maintenance diet and prescribed exercise
(3d wk-1, 3 sets, ''85 % I RM, 10—12 reps, eight lifts) beginning on d 11 of their menstrual cycle was followed by measurement of hormone response to a weightlifting bout during energy balance (EBAL) on d 18. This included blood sampling via a catheter before, just after, and at 15 and 30 mm of recovery. The women consumed 500 kcal per day for
the next 48 hrs and then repeated the weight!ifting test during negative energy balance (NEBAL). SEQ2 was similar
except that the 48 hrs of NEBAL preceded the EBAL test condition. Estradiol and beta-endorphin increased from baseline to immediately post exercise under both dietary
conditions but was significant only during NEBAL.
Female endurance athletes have repeatedly been observed to have a higher incidence of menstrual dysfunction than nonathletes (15). Data from our laboratory (29) indicate that menstrual disruption is also more common in weightlifters than non-weightlifters. Thirty percent of a group of rec-
reational weightlifters reported either oligomenorrhea or amenorrhea as compared to 13 % of non-weightlifters. Although low body fat has been suggested as a cause for a change
in cyclicity of athletes, the recreational weightlifters were of normal body fat which was similar to that of the control group. Thus, other factors must be involved in this abnormal prevalence of oligomenorrhea. Repeated acute hormonal changes associated with exercise have been suggested as a mechanism for menstrual alterations (3). For example, an increase in estradiol is known to cause a negative feedback effect on the hypothalamus to reduce gonadotropin releasing hormone (GnRH). Thus, repeated increases in this hormone could contribute to reduced stimulation of gonadotropin release from the pituitary Several studies have reported that aerobic exercise increased blood
estradiol concentration (3, 13). This hormone has not been measured with exercise which included significant anaerobic metabolism such as resistance training.
Another hormone that has been implicated in hypothalamic control of GnR}1 release is beta-endorphin
Estradiol increased 1.6 fold and beta-endorphin 3.7 fold by the end of the resistance exercise bout during NEBAL. Both hormones were also elevated for a longer time during re-
(BEND). Several recent reviews have focused on the role that this hormone may have in female reproductive dysfunction (8,
covery in the NEBAL condition. Since estradiol and beta-endorphin can suppress gonadotropin release, it is possible that repeated elevations in these hormones during weightlifting, especially concurrent with energy restriction, could contribute to disruption of the menstrual cycle.
reduced LH pulsatility (11). Thus, increases in estradiol and/or beta-endorphin could contribute to changes in GnRH release and thus menstrual cyclicity.
Key words _______________________________ Resistance exercise, beta-endorphin, estradiol, exercise, menstrual function ____________________________________________
21, 23). For example, infusion of BEND in men caused a decrease in LH (20) and injection of morphine in monkeys
Aerobic exercise has been shown to increase blood BEND concentration (25). High intensity exercise appears to be important in eliciting this hormonal response. Although resistance exercise is very intense, one study examining
the BEND response to resistance exercise, using repeated isometric contractions, did not find any increase in BEND (18). Cumming et a!. (7), however, reported increases in several other hormones associated with the reproductive cycle such as LH, FSH and testosterone in women following a weightlifting session.
mt. J. Sports Med. 13 (1992) 542—547 Georg Thieme Verlag Stuttgart New York
Weight loss appears to increase the risk of menstrual disruption. Bullen et al. (5) reported that runners who
Downloaded by: Queen's University. Copyrighted material.
.1 Walberg-Rankin, W D. Franke and F C. Gwazdauskas, Response of Beta-Endorphin and Estradiol to Resistance Exercise in Females during Energy Balance and
mt. .1 Sports Med. 13 (1992) 543
Response of Beta-Endorphin and Estradiol to Resistance Exercise in Females
ners who maintained their weight during training. This could be mediated through hormonal changes induced by energy restriction which influence gonadotropin release. For example, Dyer Ct al. (9) determined that the reduction in the magnitude of LH
pulsatility in rats undergoing an acute fast was mediated by opioid inhibition in the brain.
As reported earlier by this laboratory (29), women participating in regular resistance training had excessive concern relative to inactive women about their body weight and food consumption. Female weightlifters who compete in body
building competitions typically undergo repeated caloric restriction to achieve the extremely lean physique that is required for this sport. This negative energy balance may contribute to the increased menstrual disruption seen in this population.
This study was designed to examine several questions concerning female weightlifters. First, what is the acute effect of a typical weightlifting bout on BEND and estradiol? Secondly, is the effect of weightlifting on these hormones altered by a negative energy balance? Answers to these questions may help to explain the increased frequency of menstrual disturbance observed previously in female weightlifters.
Methods
Subjects and Design Five females involved in recreational weightlifting were recruited from a University campus weight club. The study was approved by the Institutional Review Board for Research Involving Human Subjects. All subjects were informed of risks and signed informed consents. None reported to be on birth control pills or anabolic steroids and all reported normal menstrual cycles of average length at consistent intervals. Our purpose was to recruit women who were experienced in resistance training and those who were past the initial phase of adaptation when beginning a resistance exercise program. Thus, all subjects were currently weightlifting at least three days per week (up to seven days per week) for from 30 minutes to 2 hours per session for the purpose of physique development.
They had been regularly lifting with this schedule for a minimum of 4 months and up to 5 years. Descriptive information on the subjects is supplied in Table 1.
day of cycle: 9 10 11 12 13 14 15 16 17 18 19 20 21 seq 1
oo&oôcooaoôooooooOo
seq 2
= energy maintenance
diet
A = blood sampling
+
A
A
A
A
= energy restriction wt. lifting bout
Fig. I Experimental design.
All women were asked to participate in two months of testing (Fig. 1). Each month included two tests of the acute hormonal response to weightlifting, one in energy balance
(EBAL) and one in negative energy balance (NEBAL). The order of the EBAL and NEBAL tests were changed for the two
months so that possible influence of sequence of treatment could be evaluated. Thus, one month the individual performed
the experiment in sequence 1 (SEQ1) where EBAL test preceded the NEBAIL test. Sequence 2 (SEQ2), when the order was reversed, was performed the other month. The initial assignment to SEQ 1 or SEQ2 was random.
Each month the women followed a baseline week, consisting of a prescribed weight maintenance diet of similar composition (30 keal /kg, adjusted as needed to maintain body weight, 15 % protein, 30% fat, 55 % carbohydrate) using the diabetic exchange system (1) and a similar weight training program for one week. This maintenance week began on day ii (defined as the 11th day after the start of menses) during SEQ1 and day 9 during SEQ2.
At the end of the maintenance week (d 18 for SEQ1 and d 16 for SEQ2), all women had their body composition assessed using skinfold measurement. Then, those in SEQ1 underwent a test of acute hormonal response to a weightlifting bout. This test included insertion of a catheter into a forearm vein which was kept patent with a heparin lock. After supine resting for 45 minutes the first 5 ml blood sample was withdrawn (time —60) and was considered a baseline sample. Immediately following that sampling, the subjects participated in a weightlifting session (catheter in place) of approximately one hour in duration. A second blood sample was withdrawn at the end of the exercise bout (time 0), another after 15 minutes of
recoveiy (time 15), and the last sample at 30 minutes of recovery (time 30). Subjects were seated throughout the recovery period.
Table I Subject characteristics and initial strength (1 RM) measurements. Age (yrs) Height (cm) Bodyweight (kg)
% Body Fat Bench press* (kg) Abdominal crunch (kg) Cable rows (kg) Seated press (kg) Lat pulls (kg) Leg extension (kg) Leg curls (kg) Squats (kg)
24.4 2.0 169.8 1.8 62.1
23.7 39.7 6.6 49.5
6.1
50.4 5.6 27.8 4.2 47.6 6.0
64.3 5.1 35.3
2.5
52.7 ±6.0
Values are averages SEM for five subjects. *1 RM values were estimated from tests of 5 RM.
Subjects in SEQ1 were then given a formula hypocaloric diet to consume for the next 48 hrs. No exercise
was to be done during this time period. Then, on d20 the hormonal response to weightlifting protocol was repeated.
In SEQ2, the women were prescribed the weight maintenance diet for d 9 through 15 and then given the formula hypocalonc diet to consume for 48 hrs (d 16 and 17) prior to the hormonal response to weightlifting protocol. Then,
the women consumed the diabetic exchange, maintenance energy diet for 48 hours prior to repeating the hormonal response test (d20).
Time of blood sampling during the acute weightlifting test varied between women between 10:00 am and
3:00pm depending on subjects' availability for this two hour
Downloaded by: Queen's University. Copyrighted material.
were losing weight had more menstrual dysfunction than run-
544 Int. I Sports Med. 13 (1992)
.1 Walberg-Rankin, W D. Franke, E C. Gwazdauskas
block of time but was maintained the same for both sequences in each individual subject.
Statistical procedures The hormonal response to exercise was ana-
(SEQ 1). Thus, there was a total of 9 acute weightlifting tests during EBAL and 9 during NEBAL.
Hypocaloric diet
The hypocaloric diet consisted of 2 cans of Ensure (Ross Laboratories; 250 kcai, 9.3 g protein, 8.8 g fat, 33.8 g carbohydrate per can) per day. All subjects were encouraged to drink 1 liter of water per day.
lyzed in several ways. The absolute hormone concentration for both treatments (EBAL and NEBAL) was compared over time
at the four time points using repeated measures ANOVA. In addition, the total area under the curve was computed for each hormonal response. A possible effect of sequence of treatment was tested by computing the residual effect of sequence. This repeated measures ANOVA takes both the between-subject and within-subject variance into account. Differences between individual means were assessed using a Tukey post hoc test. A p-value of
