Free weight resistance training alters body composition in middle-aged women depending on menopause - A 20-week control trial study

doi:10.21203/rs.3.rs-2845322/v1

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Research Article

Free weight resistance training alters body composition in middle-aged women depending on menopause - A 20-week control trial study

https://doi.org/10.21203/rs.3.rs-2845322/v1

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Journal Publication

published 06 Oct, 2023

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Background: Resistance training (RT) is effective in counteracting the age- and menopause-related loss of muscle mass (MM) and strength in middle-aged women (40-60 years). Research on RT with free weights in this population is limited in pre- and postmenopausal women. Based on this, a 20-week training intervention was conducted with middle-aged women to investigate the effects of systematic strength training with free weights on strength capacity and body composition.

Method: Forty-one healthy women (52.0±3.6 years) participated in this study. A 10-week control phase (no strength training, T0-T1) was followed by a 10-week intervention phase (T1-T2) with RT twice a week and 6-8 sets of each muscle per week. Subjects were randomly assigned to a low-intensity (50% 1-RM) or moderate-intensity (75% 1-RM) RT group and divided into pre-menopausal (PreMeno) and post-menopausal (PostMeno) according to their hormone profile. Fat-free mass (FFM), MM, fat mass (FM), muscle thickness (Vastus lateralis (VL), Rectus femoris (RF), Triceps brachii (TB), grip strength, 1-RM squat and bench press were assessed before and after each phase. Statistical analysis was used a linear mixed model to account for fixed (time and group) and random effects (individual).

Results: A total of 31 women successfully completed the study. No injuries occurred during the intervention. Significant increases in 1-RM were observed in all groups. No interaction effect was observed for the strength parameters. In premenopausal women, FFM, MM and RF muscle thickness increased significantly, while VL showed a trend. These effects were not present in postmenopausal women regardless of RT intensity.

Conclusion: RT with free weight is safe and effective for middle-aged women to increase 1-RM. Hypertrophy effects were found exclusively in premenopausal women. To achieve hypertrophy and/or body composition changes in postmenopausal women, larger training volumes (>6-8 sets/muscle per week) are likely required.

middle-aged women

menopause

hypertrophy

muscle mass

resistance training

strength

Loss of muscle mass (MM) is part of the ageing process [1]. MM in men and women has been shown to decrease by 3 to 8 % er decade after age 30 and 5 to 10% after age 50, correspondingly [2]. This reduction in MM and also strength during the ageing process may lead to physical disability [1], negatively affects the performance of everyday life, and increases the risks of falls and fractures [1, 3]. For context, postmenopausal women with reduced muscle mass show a 2.1-fold higher risk of falling and a 2.7-fold higher risk of bone fracture than women with preserved muscle mass [4]. Furthermore, since skeletal muscle is a metabolically strongly active tissue, common metabolic disorders associated with ageing, such as diabetes, may also be associated with the decline in MM [1]. Therefore, maintaining MM during the ageing process in men and women is crucial for musculoskeletal health[3] and for the prevention of health risk factors, such as obesity, insulin resistance, and hypertension [5], as low MM as a result of ageing is associated with overall greater mortality [6].

When considering sex-specific differences in ageing, there are important differences between biological men and women. Probably the most significant event for ageing women is menopause, which usually occurs approximately between the ages of 45 and 55 [7]. Menopause marks the end of menstruation and reproductive capacity and is associated with various physiological hormonal changes. Especially the decline in estrogen levels has detrimental effects on body composition such as an increase in fat mass (FM), a decrease in MM strength, and bone mineral density (BMD) [1, 8–11]. Consequently, as compared to males, menopausal women are at higher risk of developing osteoporosis and other musculoskeletal disorders [11, 12]. Hormone replacement therapy is feasible but is associated with side effects such as breast tenderness, enlargement, headaches, mood changes, or nausea. As an alternative or in addition to hormone replacement therapy, exercise interventions may be recommended [13]. Here, resistance training (RT) has proven to be particularly suitable, as it can counteract most of the negative effects of menopause described above. There is very good evidence that progressive RT in older adults has positive effects on lean body mass [1, 14, 15], MM [16–18], strength [3, 16, 17], functional capacity [19, 20], bone mass and BMD [3, 14]. Moreover, it reduces risks of falling and fracture [21], and it supports physical and mental well-being [22], confidence and happiness [23].

Therefore, it is not surprising that the World Health Organization recommends that all adults should do muscle-strengthening activities that involve all major muscle groups at moderate or greater intensity and at least twice a week to provide health benefits [24]. The American College of Sports Medicine (ACSM) is more specific in its 2009 guidelines for RT [25]. They state that untrained individuals should resistance train their entire body 2–3 times a week using free weights and machines (single- and multi-joint exercises) with 1–3 sets per exercise, 8–12 repetitions (60–70% one-repetition maximum [1-RM] for strength; 70–85% 1-RM for hypertrophy) and 1-3minutes of rest (depending on exercise selection). However, recent reviews show that strength and muscle growth can be achieved with any intensity and number of repetitions [26, 27]. Initial evidence proposes that the total number of sets with the appropriate correlation between the number of repetitions, intensity and rest time is critical to increase strength or muscle mass. Current research suggests that only 5–6 sets per muscle group per week are sufficient for beginners to achieve an effect [26, 27]. But, current recommendations are based on data from males. Only 2–14% of the articles in three major sports and exercise magazines included only women as participants [28], so there could be a possible gender difference in exercise recommendations. Consequently, it is important to have more high-quality research to provide sex and age-specific recommendations for effective RT programs during ageing.

Previous studies employing middle-aged and older women primarily made use of machine-based programs or a combination of machine and free-weight exercises [29, 30]. In addition, research has tended to focus on the effects of low to moderate-intensity RT programmes (around 60% 1-RM) and 8–12 repetitions [1, 30, 31] but this is not consistent with current recommendations. Usually, 15 or more repetitions are completed at an intensity of 60%, or an intensity of 70–80% is generally used for a repetition range of 8–12 repetitions [26, 27]. Besides, only a few studies compared the effects of different intensities in machine-based RT programs [32, 33, 34][35]. Moreover, “effort”, or the set endpoint and exercise velocity was rarely described [29].

However, to preserve bone health and increase strength, free weight training might be superior to machine-based programs [29, 36]. In addition, everyday movements can be ideally trained with free weights and correspond more to applied science. It is therefore surprising that, to the best of our knowledge, no studies employing middle-aged or older women have been conducted exclusively with free weights.

In summary, there is insufficient evidence to provide specific guidelines for older women, including pre-, peri-, and postmenopausal women, to optimize MM and strength gain [30]. Furthermore, the hormonal status of the participants was not or insufficiently determined before enrollment [37] and there is a lack of data on the effects of free-weight RT for middle-aged women.

Therefore, this is the first study to investigate the effects of free-weight RT on muscle strength and body composition in middle-aged women depending on hormone status (pre- and postmenopausal) and two different intensities.

Participants

All volunteers had to be healthy with no orthopaedic or cardiovascular conditions and should be able to perform a squat with the tops of their femur parallel to the floor. Therefore, seven individuals were excluded before the start of the study. After being informed about the study procedures and inclusion criteria, 41 healthy women were enrolled on the study (15/03/2021) after signing informed consent. The classification of the participants in pre-and postmenopausal was based on hormone concentrations and the date of the last menstrual period [37]. In the case of low estradiol (E2) and high follicle-stimulating hormone (FSH) concentrations, and at least 12 months without menstruation, participants were declared postmenopausal [37]. Seventeen participants (n = 17) were classified as pre- (PreMeno) and 24 as postmenopausal (PostMeno). Subsequently, postmenopausal women were assigned after stratified randomization (MM, age, weight, and height) into two subgroups: moderate intensity (MI-RT; n = 12) and low intensity (LI-RT; n = 12). Premenopausal women were not divided into subgroups due to the small sample size and performed MI-RT.

Experimental design

The study was approved by the local ethics committee of the IST University of Applied Science, Dusseldorf (02/2021)

, according to the Declaration of Helsinki, and registered in the German Registry of Clinical Studies (05/03/2021; DRKS00023826). In addition, the hygiene concept for preventing the spread of COVID-19 was approved by the local regulatory authority. A total of 41 women aged 40–60 years were recruited into a local gym. The study design encompassed two phases, and three measurement points (T0, T1, T2), and lasted for 20 weeks (see Fig. 1).

#####Figure1#####

Initially, ten weeks (T0-T1) served as a control period without any training or systematic physical activity (lockdown due to the COVID-19 pandemic). This was followed by a 10-week RT intervention period (T1-T2) using a two-group matched pair parallel design. At T0, participants completed questionnaires about their health, menstrual status, and recent RT history. Subsequently, hormone status (estradiol [E2], progesterone [P], follicle-stimulating hormone [FSH], testosterone [T], dehydroepiandrosterone [DHEA]), body composition (total body water [TBW], fat-free mass [FFM], muscle mass [MM], fat mass [FM]), muscle thickness (vastus lateralis [VL], rectus femoris [RF], triceps brachii [TB]), grip strength (GS), and dynamic strength (1-RM squat [SQ], 1-RM bench press [BP]) were assessed. The same variables were also collected after the control and RT period except for hormone status. T2 testing was done 48–72h after the last RT session.

Procedures

Forty-eight hours before testing, the subjects were not allowed to engage in resistance training or any other strenuous physical activity. The volunteers were also not allowed to drink alcohol before testing and had to appear fast. All measurements (T0–T2) were conducted single-blind in the morning at the same time of the day by the same researcher.

Hormone parameters

For saliva samples, specific ELISA kits for E2, P, T, and DHEA concentrations were used (RE52281; RE62141; RE52651; RE30121046; Re62039). Dry blood concentration of follicle-stimulating hormone (FSH) was analyzed by an external laboratory according to the CLIA method (Ayumetrix, 17387 63rd Ave, Lake Oswego, OR 97035, USA).

Body mass and body composition

Body mass [BM] was assessed by a digital scale (Etekcity EB4074C, Anaheim, CA, United States of America), with participants only wearing underwear and no shoes or socks. Total body water (TBW), fat-free mass [FFM], MM, and fat mass (FM) were analyzed by bioelectrical impedance analysis (BIA 101, Akern, Firenze, Italy). Before measurements, participants had to lie supine for ten minutes on a treatment table to allow for fluid shift [38]. Subsequently, the measurement was performed, and the data were processed using BodyGramPro software (Version 3.0, Akern, Firenze, Italy).

Muscle thickness

For muscle thickness measurements, a B-mode ultrasound (Mindray DP-50, Mindray Medical International Ltd, Shenzhen, China) with an 8.5-MHz linear probe (Mindray 75L53EA, Mindray Medical International Ltd, Shenzhen, China) was used. Muscle thickness was measured at three anatomical sites on the right side in accordance with previous studies [38, 39]. M. vastus lateralis [VL] thickness was measured with the participants lying supine on an examination table at half distance between the most prominent point of the greater trochanter and the lateral condyle of the tibia (gain 50 dB; image depth 3.7 cm). The thickness of the rectus femoris [RF] was measured at 50 % betwen the anterior inferior supra iliac crest and the proximal border of the patella with participants lying on their left side (gain 50 dB; image depth 3.7 cm). For measurement of the triceps brachii [TB], the participants lay on their abdomen while mages were taken at 40 % distl between the acromial process of the scapula and the lateral epicondyle of the humerus (gain 50 dB; image depth 5.5 cm). To ensure the identical positioning of the ultrasound probe, the measuring points were marked with a waterproof pen. Ultrasound transmission gel was applied to the scanning head, and the probe was positioned perpendicular to the long axis of the extremity without depression of the underlying tissue. Three images were recorded at each site and saved on a USB flash drive. Subsequently, muscle thickness was analyzed in the images using the calliper measurement of the ultrasound machine. The mean values of the three images of each site were used for further analyses. The test–retest intraclass correlations coefficient for this analysis was reported from our laboratory as 0.998 (RF), 0.996 (VL), and 0.997 (TB) [38].

Strength

Following a standardized warm-up procedure (5min running), grip, upper and lower body strength tests were conducted. Grip strength [GS] of both hands was assessed using a digital hand-held dynamometer (digital Jamar+, Fabrication Enterprises, New York, United States). For testing, volunteers were seated upright on a chair with elbows bent 90° and in contact with the body. Then they were instructed to press the grip of the device as forcefully as possible for at least five seconds without changing their position. Three trials were carried out for each side. The best trial was documented for further analysis. For testing lower body strength, a “touch and go” barbell box squat (SQ, femur parallel to the floor) was used. The height of the box was adjusted for each subject individually and maintained throughout the RT period and during retesting. After a minimum of five minutes of rest, upper body strength was assessed using the free weight bench press exercise (BP). For this, grip widths were documented and stipulated throughout the study. For both tests, the participants first completed ten repetitions with an empty bar, followed by a two-minute rest period. Then, a second warm-up set was completed with ten repetitions and approximately 50% of the predicted ten-repetition maximum load. Following four minutes of rest, a final set was performed until momentary concentric muscle failure or failure of proper exercise technique. To this end, a load was set in advance, which the research team estimated to allow one to ten repetitions. From the load used and the completed repetitions, the 1RM squat and bench press were calculated according to the formula proposed by Brzycki [40], which was evaluated as sufficiently accurate for estimating 1-RM using fatiguing sets of less than ten repetitions [41].

Resistance Training Protocol

A detailed description of the RT protocol (sets, repetitions, intensity, tempo, and rest) throughout the study can be found in Table 1. The training program consisted encompassed two cycles of five weeks each. Weeks one to four of each cycle were “loading” weeks followed by one “unloading” week. The training was conducted twice weekly, 48-72h apart. All RT sessions were supervised by a qualified member of the research team (researcher-to-participant ratio 1:1–4). Exercise selection was identical for all intervention groups. Session 1 consisted of “touch and go” barbell box squats (femur parallel to the floor, barbell bench press, seated neutral grip cable row, dumbbell side bend, and prone plank. In the second training session, the same exercises were completed, except that the cable row was replaced by a lat pull-down with a wide pronated grip. Except for box squats and the plank, all exercises were completed with the maximum possible range of motion and at identical tempi. Volume loads (repetitions x sets x % 1-RM) were approximately equal between intervention groups, with the MI-RT group performing more sets per exercise to achieve a similar volume load compared to the LI-RT. The adjusted weight of the box squat and bench press in the first cycle was based on the initial 1-RM test (T1), whereas the resistance of the remaining exercises was determined by trial and error. During the “loading” weeks, the last set of each exercise was performed to momentary concentric failure or failure of proper exercise technique. During the following weeks, the weight was increased by 2.5-5% for each exercise, depending on the repetition to failure. From the last set of each exercise in week 4, a new 1-RM was estimated using the Brzycki formula [40] and used from week six.

Table 1

Overview of the resistance training protocol
	Cycle 1		Cycle 2
	Week1–4 Loading	Week5 Unloading	Week6–9 Loading	Week10 Unloading
	Session 1 and 2 (sets x reps)
MI-RT Intensity	4sets 3x10 1x to failure @75% 1-RM¹⁾	3sets 3x10 @53.3% 1-RM¹⁾	4sets 3x10 1x to failure 75% 1-RM²⁾	3sets 3x10 53.3% 1-RM²⁾
LI-RT Intensity	3sets 2x20 1x to failure 50% 1-RM¹⁾	2sets 2x20 40% 1-RM¹⁾	3sets 2x20 1x to failure 50% 1-RM²⁾	2sets 2x20 40% 1-RM²⁾
Tempo Rest	2:0:1 (eccentric : isometric : concentric) 120seconds

MI-RT = moderate-intensity resistance training group; LI-RT = low-intensity resistance training; 1-RM = one-repetition maximum; ¹⁾ based on pre intervention 1-RM; ² ⁾ based on estimated 1-RM using the Brzycki formula (35) (weight and repetitions from the last set of each exercise following week 4 session 2).

Nutrition

Dietary habits were maintained throughout the 20 weeks. Only immediately after the RT sessions participants consumed a carbohydrate-protein source to maximize muscle protein synthesis. Participants could choose between three different meals with a similar amount of calories, protein and carbohydrates. Each meal was used in previous investigations [42, 43]. For detailed meal information, see the supplemental materials.

Statistical analyses

Data were analyzed by the R statistical language version 4.0.4 (R Core Team, 2021). Only data from participants with an adherence of > 85% were included in the analyses. The raw data of VL, RF, and TB were box-cox transformed before analysis. The transformation was applied to obtain approximately Gaussian distributions of the raw data which exhibited heavily skewed distributions otherwise. Transformations were applied to the data at T₀ and the box-cox estimates for λ were then employed to transform the remaining data.

The values of FFM, MM, FM, GS, 1-RM SQ and BP were analyzed unchanged. Individual time intervals (∆t [h]) since the start of the study were introduced as an additional covariate. Data analysis was performed using linear mixed effects (LME) models, where FFM_λ, MM_λ, FM_λ, VL_λ, RF_λ, TB_λ, GS, 1RM SQ and BP, served as dependent variables. Model building was performed independently for each of these.

We were specifically interested in the effects of menopause on the trends of strength capacity and muscle growth. Therefore, all models included the interaction term of menopause with PreMeno MI-RT (T0 to T2) as a fixed effect. Likewise, PreMeno MI-RT itself was axiomatically included as a fixed effect. As it represents an ordered factor with three levels, second-order orthogonal polynomials were chosen as contrasts for PreMeno MI-RT.

Initially, random effects were merely assumed between individual intercepts of each measure. Subsequently, ∆t was included as a random effect, where linear individual trends were assumed. The presence of potentially non-linear individual trends then was investigated by upgrading to 2nd or 3rd-order natural splines of ∆t. After the development of appropriate random effect structures, it was tested whether ∆t also contributed to general trends in the population, i.e., whether it represented a significant fixed effect. In either case, model comparisons were based on likelihood statistics and changes in Akaike’s information criterion. Significant differences were set with p ≤ .05.

Finally, effect sizes were determined between discrete time levels according to the approximation of Cohen's d for mixed effects models (d = 2t/DF^(1/2) where t = t-value; DF = degrees of freedom. Classifications were stipulated as follows: trivial < 0.2; small < 0.5; moderate < 0.8; strong > 0.8 [44]. All graphs were created using the latest version of GraphPad Prism.

Five participants missed T1-testing and were therefore excluded from the second part of the study. Another five participants missed more than three RT sessions (adherence < 85%) during the intervention period (T1–T2) and were therefore also excluded from the final analysis. The reasons for absence were non-study-related injury or illness (n = 4) and another personal bother (n = 6). No injuries occurred during the RT intervention. In total, 31 subjects completed the study. Anthropometric data and the hormone concentration of the three training groups are summarized in Table 2.

Table 2

Descriptive data and hormone concentration
	PreMeno MI-RT			PostMeno MI-RT			PostMeno LI-RT
	T0	T1	T2	T0	T1	T2	T0	T1	T2
Age (years)	47.4 ± 5.3			54.3 ± 4.7			55.6 ± 2.9
Height (cm)	167.5 ± 8.4			166.0 ± 7.2			166.6 ± 5.9
E2 (pg/ml)	7.4 ± 17.1	n.a	n.a	1.1 ± 1.0	n.a	n.a	1.5 ± 1.2	n.a	n.a
P (pg/ml)	58.4 ± 40.2	n.a	n.a	51.2 ± 24.5	n.a	n.a	30.3 ± 11.8	n.a	n.a
FSH (mlU/ml)	16.7 ± 19.0	n.a	n.a	86.2 ± 33.9	n.a	n.a	96.5 ± 16.7	n.a	n.a
T (pg/ml)	14.4 ± 6.4	n.a	n.a	15.7 ± 7.9	n.a	n.a	16.0 8.2	n.a	n.a
DHEA (pg/ml)	170.9 ± 72.0	n.a	n.a	195.6 ± 90.6	n.a	n.a	179.9 77.9	n.a	n.a
PreMeno = premenopause; PostMeno = postmenopause; MI-RT = moderate intensity resistance training; LI-RT = low intensity resistance training; BMI = body mass index; DHEA = dehydroepiandrosterone; E2 = estradiol; FSH = follicle stimulating hormone; n.a. = no analyses; P = progesterone; T = testosterone

Body composition

Body weight and BMI did not change significantly in all three groups during the entire period (weight: p = .494; BMI: p = .559). No difference between the groups could be determined for the weight (PostMeno MI-RT: p = .992; PostMeno LI-RT: p = .131) and BMI (PostMeno MI-RT: p = .503; PostMeno LI-RT: p = .115).

For FFM, only a significant increase was observed in the PreMeno MI-RT group (p = .015) (first order). The effect between T1 and T2 in the PreMeno MI-RT group was small (d = 0.29). In addition, an interaction effect (first order) of both PostMeno and PreMeno MI-RT could be identified (PostMeno MI-RT: p = .032; PostMeno LI-RT: p = .022). Unlike the PreMeno MI-RT group, the two PostMeno groups showed no increase in FFM (Fig. 2a).

In MM, only a significant increase was observed in the PreMeno MI-RT group (p = .002) (second order). The effect between T1 and T2 in the PreMeno MI-RT group was strong (d = 1.25). Additionally, the group effect (second order) of both PostMeno and PreMeno MI-RT could be identified (PostMeno LI-RT: p = .030; PostMeno LI-RT: p = .024). Unlike the PreMeno MI-RT group, the two PostMeno groups did not have an increase in MM (Fig. 2b).

In FM, only a significant decrease was detected in the PreMeno MI-RT group (p = .039) (first order). The effect between T1 and T2 in the PreMeno MI-RT group was moderate (d = 0.57). A Time*group interaction was only between the PostMeno LI-RT to the PreMeno MI-RT group (p = .039) (second order). In contrast to the PreMeno MI-RT group both PostMeno groups had no decrease in FM (Fig. 2C).

##### Fig. 2 #######

Muscle thickness

A significant difference over time was observed in the RF (p = .004) (first order). Different curve progression could not be detected (PostMeno MI-RT: p = .210; PostMeno LI-RT: p = .300) (first order). The effect between T1 and T2 in all groups was moderate to strong (PreMeno MI-RT: d = 0.80; PostMeno MI-RT: d = 0.46; PostMeno LI-RT: d = 0.52) (Fig. 3a).

Trends over time could be identified in the VL (first order: p = .050; second order: p = .079). In the PreMeno MI-RT and PostMeno MI-RT groups, a small to moderate effect was found between T1 and T2 (PreMeno MI-RT: d = 0.54; PostMeno MI-RT: d = 0.43). In addition, a trend in the curvature could be observed between the PreMeno MI-RT and the PostMeno LI-RT group (p = 0.58) (first order) (Fig. 3b).

In the TB, no significant difference over time could be detected (first order: p = .72; second order: p = .83). In addition, no group differences were observed (Fig. 3c).

###### Fig. 3#####

Strength

All three groups increased their SQ performance significantly (first order: p = .000 and second order: p = .002). No group differences were observed in SQ performance (PostMeno MI-RT: p = .257; PostMeno LI: p = .913 first order) (Fig. 4A). A strong effect was detected over time for all groups (PreMeno MI-RT: d = 1.51; PostMeno MI-RT: d = 1.52; PostMeno LI-RT: d = 1.64 second order). Each group improved significantly in BP performance (first order: p = .000 and second order: p = .000) (Fig. 4B). No significant difference in curve progressions could be observed between the groups. (PostMeno MI-RT: p = .712; PostMeno LI-RT: p = 795, first order). A moderate to strong effect over time was detected for each group (PreMeno MI-RT: d = 0.66; PostMeno MI-RT: d = 0.98; PostMeno LI-RT: d = 0.84 second order). In grip strength, an identical development was found for the left and right hand and was summarized as one score. Both the first and second-order terms were significant (first order: p = .000 second order: p = .000)(Fig. 4C&D). No differences were detected between the three groups (PostMeno MI-RT: p = .548; PostMeno LI-RT: p = .675, first order).

####Figure 4#####

All results are summarized in Table 3.

Table 3

all results of body composition, muscle thickness and strength capacity
	PreMeno MI-RT			PostMeno MI-RT			PostMeno LI-RT
	T0	T1	T2	T0	T1	T2	T0	T1	T2
Weight (kg)	76.19 ± 16 .31	76.18 ± 16.18	75.62 ± 16.54	70.29 ± 8.61	70.43 ± 8.83	70.04 ± 8.33	71.10 ± 8.52	69.68 ± 7.90	69.56 ± 8.35
BMI (kg/m²)	27.28 ± 5.78	27.25 ± 5.95	27.03 ± 5.82	25.81 ± 2.15	25.52 ± 2.48	25.37 ± 2.26	25.62 ± 2.79	25.06 ± 2.90	25.12 ± 3.06
FFM (kg)	49.58 ± 6.78	50.08 ± 5.41	51.97 ± 6.99*	47.70 ± 3.63	48.07 ± 3.89	46.99 ± 4.41#	49.49 ± 5.47	49.20 ± 4.61	48.46 ± 4.00#
MM (kg)	30.48 ± 4.77	29.18 ± 3.95	31.88 ± 7.05*	27.98 ± 2.22	27.78 ± 2.34	27.59 ± 2.74#	30.56 ± 3.47	29.80 ± 3.24	28.77 ± 2.09#
FM (kg)	26.44 ± 11.13	26.09 ± 12.22	24.82 ± 10.77*	23.49 ± 6.40	22.84 ± 7.25	23.10 ± 6.07	21.61 ± 3.74	20.48 ± 3.93	21.32 ± 4.85#
VL (cm)	2.39 ± 0.42	2.40 ± 0.45	2.62 ± 0.48*	2.25 ± 0.48	2.29 ± 0.53	2.41 ± 0.51	2.26 ± 0.56	2.15 ± 0.62	2.15 ± 0.55
RF (cm)	1.95 ± 0.85	1.98 ± 0.84	2.18 ± 0.85*	2.13 ± 0.66	2.07 ± 0.68	2.23 ± 0.66*	1.84 ± 0.48	1.77 ± 0.49	1.95 ± 0.47*
TB (cm)	3.29 ± 0.39	3.29 ± 0.47	3.26 ± 0.46	3.01 ± 0.58	2.87 ± 0.50	2.96 ± 0.54	3.11 ± 0.60	3.20 ± 0.56	3.31 ± 0.66
GS left (kg)	23.12 ± 4.16	30.32 ± 5.51*	29.16 ± 5.26	24.16 ± 4.53	31.52 ± 3.78*	30.96 ± 3.46	21.99 ± 5.84	27.20 ± 5.11*	28.74 ± 4.39
GS right (kg)	23.95 ± 4.28	31.45 ± 5.72*	31.27 ± 6.23	24.59 ± 5.01	33.30 ± 3.61*	33.09 ± 4.48	22.68 ± 4.76	29.80 ± 5.85*	29.76 ± 4.46
1-RM SQ (kg	37.91 ± 12.99	40.85 ± 14.83	65.80 ± 18.76*	39.01 ± 19.64	36.83 ± 21.45	60.71 ± 18.91*	34.27 ± 8.07	35.49 ± 9.20	62.77 ± 15.87*
1-RM BP (kg)	27.24 ± 4.86	29.77 ± 5.92	35.12 ± 7.10*	25.83 ± 3.19	27.01 ± 2.95	33.05 ± 5.45*	25.98 ± 3.58	27.47 ± 3.18	33.38 ± 3.62*
PreMeno = premenopause; PostMeno = postmenopause; MI-RT = moderate intensity resistance training; LI-RT = low intensity resistance training; FFM = fat free mass; FM = fat mass; MM = muscle mass; VL = vastus lateralis; RF = rectus femoris; TB = triceps brachii; GS = grip strength; 1-RM SQ = one repetition maximum squat; 1-RM BP = one repetition maximum bench press; * = significant time effect; # = significant time*group (interaction) effect

This study investigated, the effectiveness of systematic RT using free weight on strength, and body composition in middle-aged women (40–60 years). For this purpose, a 20-week training study with two phases was conducted. The results show different effects on body composition for pre and postmenopausal women, but not on strength gain. Premenopausal women with higher E2 concentrations and an active menstrual cycle significantly increased their FFM, MM and muscle thickness in VL. This effect was not observed in postmenopausal women regardless of the intensity of the training.

In general, there is a lack of studies concerning RT in middle-aged women using only free weights. However, flexion and extension movements in the hip joint as well as traction and compression stresses in the shoulder joint are everyday loads for active persons. Free weight exercises, such as squats and bench presses, that train these movements used in everyday life may be ideal to increase strength at higher degrees of specificity rather than machine-based training [29, 36]. Studies comparing the effects of only free weight RT over machine-based intervention in the elderly are currently lacking. But the present study was able to demonstrate that free-weight RT can be used safely and effectively with middle-aged women.

In addition, our results demonstrate that low and moderate-intensity RT using free weights is effective for increasing strength in pre- and postmenopausal women, both in the upper and lower body. These findings corroborated observations from previous studies based on younger participants [36, 45, 46]. For example, Botero and colleagues showed that with three RT sessions per week over 12 months, the BP and leg press performance could be increased [47]. The strength increases in our study are comparable to the effects reported in previous research [48, 49]. In comparison, Karaslaan and colleagues showed a stronger effect with 4 training sessions/week for 12 weeks with machine-assisted training [50]. Similar to male participants, the studies on middle-aged women show a comparable dose-response relationship in the adaptation processes of muscular strength [51]. Interestingly, no differences were detected between pre- and postmenopausal women in this study. The change in endocrine homeostasis probably has no significant effect on strength capacity in untrained healthy middle-aged women. In this population, other factors such as neuronal activation presumably could play an important role in the first few weeks of strength training. But currently, there is no evidence of how many training sessions are needed to focus on endocrine homeostasis for strength adaptations without clear neuronal adaptations. Therefore, the influence of endocrine homeostasis in trained women cannot be answered at this time, as no studies are available.

Compared to dynamic strength, there was no increase in isometric grip strength in any group after the training intervention. On the contrary, a significant increase was observed after the end of phase one in all groups despite this phase serving as a control period without RT. The adaptation effects will be due rather to learning effects since no RT was conducted at this time. Surprisingly, grip strength did not improve during the subsequent intervention period, although most exercises conducted require a strong grip, e.g., lateral flexion, barbell row, and lat pull, which could have resulted in increments of grip strength. Similar to the data presented here, RT on machines for 12 weeks and three training sessions per week did not induce any effects on grip strength [52]. Interestingly, grip strength is an important predictor of muscle status [53] and it is regularly employed to estimate the risk of all-cause mortality in the elderly [54]. However, if total body strength can be improved by RT with free weights but not grip strength, the relationship between grip strength, muscle status and therefore mortality may be needed to be re-examined.

Unlike muscular strength, significant differences between premenopausal and postmenopausal women could be identified for FFM and MM. Significant curve progression could only be observed in the PreMeno MI-RT group. Furthermore, a negative trend was observed in the PostMeno LI-RT group. Compared to the PostMeno MI-RT group, MM decreased by -1.8 ± 2.0kg between T0 and T2 (Table 3). Although there is no significant difference between PostMeno MI-RT and PostMeno LI-RT, the first indices suggest that this trend could not be observed in the PostMeno MI-RT (-0.4 ± 2.4kg). These results are in line with the observations of Karaaslan et al., who observed that despite twelve weeks of interventions with 4 low-intensity (40–50% 1-RM) training sessions per week, the lean body mass decreased significantly. This result was not observed in the higher-intensity training group (70–80%) [50]. In addition, results by Oliveira et al. show that a higher training volume per week induces stronger muscle growth in postmenopausal women than in low-volume training [55]. Both intervention groups performed machine-based training at an intensity of 80% 1-RM over 12 weeks with 3 training sessions each. The high-volume group had a total of 15 sets per exercise and week from week 3, whereas the low-volume group had only nine sets per week per exercise [55]. Consequently, both training groups performed more training sets per week than the PostMeno LI-HT (six sets per week) and the PostMeno MI-HT (eight sets per week). Kang and colleagues also observed significant muscle growth through RT after 12 weeks [52]. Similarly to de Oliveira, three training sessions with three sets per exercise were performed. In contrast to de Oliveria and the conducted intervention, a total of 7 exercises were performed. The intensity of the exercises ranged from 55–65% 1-RM [52]. Consequently, it can be assumed that hypertrophy can be also induced with a higher training volume with moderate intensity. In contrast to the BIA results as an indirect method for determining MM, muscle thickness measurement showed a significant increase for RF over time, but no group differences. Moreover, in VL a trend over time (p = .050) and different curve progressions (p = .058) could be detected between the PreMeno HI-RT and PostMeno LI-RT groups. These results suggest that MI-RT leads to superior adaptations in terms of muscle thickness compared to LI-RT. This is in line with the BIA results. However, there are no comparable data from previous studies.

FM significantly decreased only in the PreMeno MI-RT group. The results of both postmenopausal groups do not confirm observations of previous studies. Both Kang et al. [52] and Delshad et al. [56] observed a significant decrease in body fat after 12 weeks of RT. Similarly to the effects on MM, training frequency and volume also play a decisive role in fat mass. This assumption can be supported by the results of Rodrigues et al. where in a 12-week intervention study with two training sessions per week, including RT and endurance exercises, FM does not decrease [57]. The intensity of the training was controlled by a subjective Effort Perception Scale maintaining intensity between 13 and 15 [57]. Therefore, both the intensities and frequencies of the strength and endurance parts presumably were too weak to activate fat metabolism.

Limitations

Besides the important new findings, this study also has some limitations. One important factor is the small sample size of the individual training groups so the observations must first be regarded as initial evidence. Although there was great interest in this study among women in this age range, almost 15% of those interested had to be excluded before the study began due to lack of mobility. In addition, training sessions were quickly cancelled due to family reasons. Although the study was designed with the minimum dosage of two 60-minute training sessions per week, the well-being of the family is given higher priority than personal health. Nevertheless, all participants reported that they enjoyed training with free weights and were able to better manage their daily lives.

Another limitation of this study is the documentation of diet during the intervention. It was not possible to monitore the diets of all participants with a food diary over the whole duration. Therefore, only the protein and carbohydrate intake directly after the training was ensured to stimulate protein biosynthesis as quickly as possible and to promote regeneration in the best possible way. Even if the participants were instructed not to change their diet, this could also affect the results. Furthermore, it is not possible to say whether the participants had sufficient protein intake to promote muscular adaptation in the best possible way. Therefore, future studies with this population should consider diet and especially protein intake. Due to the hormonal changes and body composition in postmenopausal women, protein intake should be calculated based on fat-free mass to ensure the best possible feasibility.

In conclusion, the results of this study show that free weight RT is generally safe and effective for middle-aged women. Free weight moderate intensity RT two times per week leads to an increase in 1-RM squat and bench press performance as well as to an increase in muscle mass and a decrease in fat mass in premenopausal middle-aged women. In postmenopausal women, RT induces an increase in dynamic strength but not in muscle mass can be induced by RT irrespective of intensity. However, there is some evidence that a higher intensity led to better effects on muscle mass. It seems that the general recommendations for anaerobic exercises, such as strength training, do not lead to an increase in muscle mass and a decrease in fat mass in postmenopausal women [24, 58]. It seems that postmenopausal women require more than two training sessions and more than six to eight sets per exercise/week, as well an intensities of more than 50% 1-RM to change body composition. These hypotheses are supported by two meta-analyses of dose-response relationships for older persons [59, 60].

Acknowledgments

The authors would like to thank all subjects for their voluntary participation and ensure that all participants consented to the acknowledgement.

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by DK, TH, AE, and UF. The first draft of the manuscript was written by EI, KH, and SG and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Competing interests

The authors declare no competing interests

Consent Publication

All authors and participants agree to publish the collected data anonymously. Furthermore, the graphics and tables were created by the authors themselves and no third party has a claim to the illustrations. All methods used (analyses and training protocol) comply with the ethical and scientific standard of the Declaration of Helsinki and were reviewed and declared safe by the IST Ethics Committee. Furthermore, all methods used have been applied in previous research of our working group [38,61,62].

Ethical approval and informed consent

This study has been reviewed by the Local Ethics Committee of the IST University of Applied Sciences, Düsseldorf, Germany and has a positive ethical vote (02/2021). In addition, it would be registered in the German registry for clinical studies. All participants had to sign a written informed consent form before the start of the study (05/03/2021; DRKS00023826).

Data availability statement

The raw data of the participants can be requested from the corresponding authors if required. All data was encrypted so that it cannot be traced back to individual persons.

Founding

This research has not been externally funded by any third party or has any influence on the data evaluation and interpretation.

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No competing interests reported.

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Free weight resistance training alters body composition in middle-aged women depending on menopause - A 20-week control trial study

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Abstract

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Introduction

Methods

Participants

Experimental design

Procedures

Hormone parameters

Body mass and body composition

Muscle thickness

Strength

Resistance Training Protocol

Nutrition

Statistical analyses

Results

Body composition

Muscle thickness

Strength

Discussion

Limitations

Conclusion

Declarations

Acknowledgments

Competing interests

Data availability statement

References

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