Effects of a low intensity strength training program on overweight / obese and premenopausal / menopausal women

Obesity-related complications may be compounded by the detrimental consequences of menopause. Strength training programs may have an impact on this relationship. Our objective was to examine strength (1RM) and kinanthropometric alterations for overweight/obese preand menopausal women who participated in a strength program. Methods: 35 women were separated into: overweight premenopausal (n=8), obese premenopausal (n=9), overweight menopausal (n=8) and obese menopausal (n=10) categories. Participants attended a strength program for 8 weeks. Kinanthropometric characteristics and 1RM were determined at baseline, week 4 (except 1RM) and week 8. Results: All groups reduced (p< 0.05) body weight, body mass index (BMI), skinfolds and waist circumference. Furthermore, all groups achieved an increase (p< 0.05) in 1RM. When grouped per menopausal state or BMI, a more significant increase in strength was seen in menopausal and obese subjects. A significant correlation was observed for menopausal state, BMI and strength. The strength changes were significantly superior vs. kinanthropometric changes. Within kinanthropometric changes, skinfolds exhibit a more significant reduction vs. body weight, BMI and waist circumference. Conclusions: all groups showed changes in strength and kinanthropometric parameters. Strength adaptations were superior in menopausal and obese women. The strength adaptations exhibit a superior magnitude vs. kinanthropometric changes. In short term, a strength program may lead to important health and functional benefits, especially in menopausal or obese women.


INTRODUCTION
The ENS survey, conducted in 2009-2010, has provided evidence that more than 64% of women in Chile, older than 17 years, are overweight or obese 1 .
Obesity/overweight is a highly prevalent chronic disease associated with numerous co-morbidities including cardiovascular disease, diabetes, hypertension, some types of cancer 2,3 , and functional/mobility impairment 4,5 .
Moreover, obesity-related complications may be compounded by the detrimental consequences of menopause 4,6 .The confluence of aging and obesity may create an ideal environment for skeletal muscle catabolism and decline in physical function (strength).During menopause there is an altered hormonal status (less anabolic), that is aggravated by obesity, leading to decreased muscle mass and development of sarcopenic obesity, a condition that may be translated into a reduced ability to perform daily activities such as walking, chair rising, stair climbing, body transfer, among others 7 .
The relationship between obesity, increased age and physical disability will increase from the year 2012 8 onwards.Treatment for obesity has proven difficult, with a high proportion of those who lose weight, subsequently regaining much of the weight loss 9 .The high prevalence of obesity, the increasing relationship between obesity-aging-physical disability and the lack of treatment success argue for the evaluation of strategies to prevent/ treat overweight and obesity.There is widespread consensus that lifestyle changes, such as increased skeletal muscle activities, are the cornerstones in both prevention and treatment of obesity and the metabolic syndrome 10 .
Strength training must be an integral part of adult fitness programs 11 .Unlike aerobic exercise, which results in significant increases in energy expenditure during, and for a short time following cessation of the activity, the energy expenditure during strength training is relatively low 12,13 , but the increase in energy expenditure after cessation of the activity may be elevated 14 .A strength training session of minimum volume (11 min per session) demonstrated a significant effect on post exercise energy expenditure and fat oxidation 15 .Furthermore, strength training has demonstrated a beneficial effect on body composition in overweight/obese postmenopausal 16 and premenopausal women 17,18 .
The objective of the present study was to determine the effects of a guided short duration low intensity (but metabolically strenuous) strength training program with kinanthropometric measurements and muscle strength in overweight/obese and premenopausal/menopausal women.In contrast to other studies published so far, we investigated whether such an intervention would produce different results in premenopausal versus menopausal women.In addition, the effects of overweight/obesity on the outcome of the intervention were also assessed.

METHODS
Thirty-five women from Las Huellas and Folilco Family Health Center (Los Lagos city, Chile) were enrolled in this 8 week intervention.Inclu-sion criteria: female gender, sedentary lifestyle (exercise <30 min/week), glycemia <100 mg/dl, age between 18 and 65 years, body mass index (BMI) between 25 and 35, and absence of contraindication to exercise.Also, direct descendants of parents with diabetes type 2 were included, because there is little scientific evidence regarding their response to a strength training program.All subjects completed a comprehensive medical examination and routine blood tests.Subjects were excluded if they had arrhythmia, tachycardia and/or chronic obstructive pulmonary disease, osteoarticular disease, ischemia; or were taking drugs or medication that affected body weight or metabolic variables.Seventeen participants were premenopausal, 18 were classified menopausal (41 -68 years).Menopause classification was performed by anamnesis and hormonal analysis.If follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were higher than 20 IU/ ml and estradiol <30 pmol/l participants were classified as menopausal 19 .Sixteen participants were classified as overweight (BMI 25-29.8kg/m 2 ) and nineteen were classified as obese (BMI 29.9-35 kg/m 2 ) 1 .
Written informed consent was given for all subjects; the study protocol was approved by the ethical committee of the Los Lagos Family Health Center (Los Rios Region, Chile) and the Physical Activity Sciences Department of Los Lagos University (Los Lagos Region, Chile).
Data collected at baseline, and at the end of weeks 4 and 8, included body weight, height, BMI, waist circumference, and skinfolds (triceps, subscapular, iliac crest, medial calf).Maximal strength (1RM) in squat (SQ), bent row (BR), shoulder press (ShP) and biceps curl (BC) exercises were also assessed at baseline, and at the end of week 8.
All subjects were instructed not to change their dietary or physical activity habits during the 8 week intervention period.

Anthropometry
Height was measured while subjects were barefoot with a professional stadiometer (Health o Meter ® , USA), recorded to the nearest 0.1 cm.Weight was measured with the participants wearing light clothing or underwear, and was recorded to the nearest 0.01 kg using a digital scale (OMRON ® , Model HBF-INT).BMI was calculated according to weight divided by height squared (kg/m 2 ).Waist circumference was measured at the level midway between the lowest rib margin and the iliac crest to the nearest 0.5 cm, with a flexible and inextensible metric tape and precision of 0.1 cm (Hoechstmass®, West Germany 1-150 cm).All kinanthropometric measurements (including skinfolds and waist circumference) were determined by the ISAK anthropometric protocol 20 .All the measurements were obtained by the same person, with a certified ISAK level III.

Maximal strength test (1RM)
Maximal strength (1RM) of the lower (SQ) and upper body (BC, ShP, BR) was determined with free weight equipment, according to previous recomendations 21 .Previous to the 1RM test, subjects took part in 3 familiarization sessions (over a 1 week period), where the correct execution technique of the exercises performed was stressed.All measurements were taken at baseline and at week 8.

Strength training
Subjects attended twice-weekly 24-40 minute guided low intensity (but metabolically strenuous) strength training sessions during eight weeks.The training sessions were supervised by a trained exercise counselor.Adherence was assessed by participant attendance at the sessions.Adherence was good, as participants attended more than 80% of the sessions.Participants completed 4 strength exercises each session (SQ, BR, ShP and BC).The training program considered the progressive overload principle.During weeks 1-3 subjects completed 3 series for each exercise, with 20%1RM.During weeks 4-6 subjects completed 4 series for each exercise with 25% 1RM.The last 2 weeks, subjects completed 5 series for each exercise with 30%1RM.Repetitions in each series were completed until voluntary exhaustion (usually 1 minute of muscular work).A rest period of one minute was allowed between series and exercises.

Statistical analysis
Data is presented as mean ± standard deviation.The Shapiro-Wilk´s W and Levene´s tests were applied to determine normal distribution and homogeneity of variances, respectively.All study variables had a normal distribution.Therefore, ANOVA 4 × 2 (groups × time) repeated measurements were used to determine differences (in time or between groups) for the dependent variables.When a significant F value was achieved across time or between groups, Ficher LSD post hoc procedures were performed to locate the pairwise differences between the means.One way ANOVA was applied to determine differences between groups for the percentage modifications in time of the dependent variables.T-test for independent samples was used to determine significant differences between the percentage modifications of the dependent variables (variables were treated as independent samples).Pearson´s correlation was used to establish the relationship between age, body weight, BMI, waist perimeter, skinfolds and 1RM modification.All statistical analysis was applied through the computational software STATISTICA (version 6.0, StatSoft, Inc, Tulsa, Oklahoma, USA).Statistical significance was set at p<0.05.
The descriptive characteristics of subjects at baseline and at the end of weeks 4 and 8 are summarized in Table 1.
When grouped for menopausal state (data not shown) at baseline, body weight, BMI, skinfolds, waist circumference, and maximal strength, did not differ between pre-and menopausal women.On the other hand, when grouped per BMI (data not shown), body weight, BMI, waist circumference, and subscapular skinfolds were different at baseline between overweight and obese women.
No significant differences were observed between groups for the percentage changes (between weeks 0 to 8) of the dependent variables, except for BR, where ObM and OvM had a more significant increase than OvPre, and OvM had a more significant increase than ObPre.
When grouped per BMI, obese subjects had a more significant increase in maximal strength in the BC (27.3%) and BR (27.5%) exercises vs. overweight subjects (20.1 and 18.7%, respectively).All the other variables modifications were similar between obese and overweight subjects.
When grouped per menopausal state, menopausal women had a more significant increase in maximal strength in the BC (27.2%),ShP (27.7%) and BR (27.9%) exercises vs. premenopausal subjects (20.6, 22.1 and 18.9%, respectively).All the other variables' modifications were similar between menopausal and postmenopausal subjects.
Age and BMI showed no significant correlation with kinanthropometric changes.Only the 1RM increase in SQ showed a significant correlation (r=0.45;p<0.007) with age.BMI only correlates with 1RM increase in ShP (r=0.37;p=0.03) and BR (r=0.47;p=0.005).
When grouped as a whole, the percentage change of body weight (-2.4%) and BMI (-2.4%) during the 8 week intervention was significantly less than the percentage change of waist circumference (-4.3%) and the four skinfolds (-13.5, -14.5, -16.9 and -12.3% for triceps, subscapular, iliac crest and calf, respectively).The waist circumference percentage change was significantly less than the four skinfolds percentage changes.There was no significant difference between the percentage changes of the four skinfolds.The percentage change in maximal strength in BC (24%), ShP (26%), SQ (23.5%) and BR (23.5%) was significantly superior vs. all other variable changes.No significant differences were observed between the percentage changes of maximal strength in the four exercises.

DISCUSSION
We found that an 8 week guided low intensity (but metabolically strenuous) strength training program led to a substantial and significantly favorable reduction in kinanthropometric risk factors in both pre-and menopausal women, with overweight or obesity.Other strength training studies have also demonstrated a beneficial effect on kinanthropometric variables in overweight/obese postmenopausal 16 and premenopausal women 17,18 .
Strength training may have a positive impact on weight management as a result of increased fat-free mass (FFM) 22,23 and increased fat oxidation 15,24 .
Increased FFM may result in increased resting metabolic rate (RMR) 25 and increased physical activity energy expenditure (PAEE) 26 .Also, strength exercises may acutely elevate the energy expenditure.It has been shown that after a strength training session (similar to the training sessions used in our investigation) 14 RER fell from 0.9 to 0.79-0.84,and the rest oxygen consumption increased from 3.3 ml/kg/min to 3.9 ml/kg/min during 48 h.If this data is extrapolated to our investigation subjects, and considering that mean body weight of subjects was 74.7 kg, this will translate into an extra 129 L of oxygen consumption during a 48 h period.If 1 liter of oxygen is equivalent to 5 kcal 27 , subjects have expended an extra 645 kcal during this period.Thus, hypothetically, with 2 strength training sessions per week, for 8 weeks, subjects had expended an extra 10320 kcal during this period, equivalent to 1.2 kg of fat mass 28 , close to the mean 1.85 kg of body weight lost by the study subjects.Therefore, it is not unconceivable that the strength training program applied had induced a significant weight reduction, independent of diet modification.These results support recommendations by various health organizations to include RT as part of a healthy Lifestyle 11 .
It was observed that the four skinfolds assessed were significantly reduced after training (-13.5, -14.5, -16.9 and -12.3% for triceps, subscapular, iliac crest and calf, respectively).The reduction in the four skinfolds was similar.It may be argued that part of the skinfolds reduction may be attributed to a mechanical effect, where an increased muscle mass following the strength training may compress de skinfolds; but this phenomenon is not significant in women 29 .Thus, the strength training protocol described in this study may provide an attractive alternative to aerobic exercise programs for body composition modification Obesity-related complications may be compounded by the detrimental consequences of menopause 4,6 .The confluence of aging and obesity may create an ideal environment for skeletal muscle catabolism and decline in muscle mass (sarcopenic obesity), strength and reduced ability to perform daily activities such as walking, chair rising, stair climbing and body transfer 7 .In our study, subjects of all groups exhibit a significant increase in muscle strength (24, 26, 23.5 and 23.5% for BC, ShP, SQ and BR, respectively).In fact, menopausal and obese women showed a significantly superior increase of maximal strength vs. premenopausal or overweight women, indicating that strength training programs may have a positive impact on the increased prevalence of the obesity-aging-disability triad 8 .
When subjects were grouped by menopausal state, no significant differences were observed for the dependent kinanthropometric variables, but when grouped for BMI, significant differences were observed, indicating that BMI, not menopausal state, is the major contributing factor to kinanthropometric risk factor.
The study had several limitations.First, we did not control caloric intake during intervention.This may have affected the kinanthropometric variables, although all subjects were instructed not to change their dietary habits during the 8 week intervention period.Secondly, we did not control objectively physical activity level during the intervention period, although all subjects were instructed not to change their physical activity habits during the 8 week intervention period.Finally, the adherence to the intervention program is another confusion factor.For this reason analyses were adjusted per adherence level.

CONCLUSIONS
A guided short duration low intensity (but metabolically strenuous) strength training program induced substantial and significant changes in kinanthropometric parameters in overweight or obesity, pre-or menopausal women with no significant differences between these groups.The obese and/or menopausal women may be particularly respondent to the strength stimulus of strength training exercises.
The results of this study may suggest that programs designed to intervene in overweight or obesity and pre-or menopausal women by means of strength training, should be part of obesity management action in this population group.Implementation of the program described in this study has considerable potential in other situations, given that the physical space required is widely available in other realities and it relies on the use of lowcost, easily obtainable equipment.

Table 1 .
Individual, kinanthropometric and strength characteristics of subjects.