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Abstract

BACKGROUND:

Combining strength training (ST) with unstable surfaces (US) is a promising complementary approach to traditional ST to optimize muscle strength and balance in different populations.

OBJECTIVE:

To evaluate the effects of traditional ST and ST+US on grip strength, flexibility and quality of life in older women.

METHODS:

Fifty-eight older women were randomly assigned into ST ( $n=$ 22), ST $+$ US ( $n=$ 22) or control ( $n=$ 14) group. Exercise groups performed whole-body, moderate-intensity strength exercises, thrice a week during 24-weeks. ST $+$ US participants performed the same exercise prescription progressively adding unstable surfaces and devices. Dependent variables (grip strength, flexibility and health-related quality of life) were measured at baseline, 12-weeks and after 24-weeks of intervention.

RESULTS:

At completion of 24-weeks, compared with control group, traditional ST promote flexibility gains [SRT $=$ $+$ 5.42 cm (95% CI $=$ 1.01 to 9.83)]. Both training regimes improved quality of life [ST $=$ $+$ 9.50 (95% CI $=$ 1.80 to 17.20); ST $+$ US $=$ $+$ 15.23 (95%CI $=$ 7.37 to 23.08). No significant between-group difference was observed for grip strength at completion of the intervention.

CONCLUSION:

Traditional strength exercises were effective to improve flexibility and health-related quality of life among healthy older women. Combining unstable devices with traditional exercise did not provide additional gains in order to promote flexibility and quality of life.

Keywords

Resistance training muscle strength flexibility quality of life aging

1. Introduction

The physical decline which occurs with aging alters physical fitness components such as strength, flexibility and balance, leading to frailty and increased chances of falls in older adults [1, 2, 3]. Strength training (ST) has been widely recommended as a strategy to improve health parameters and functional independence in older adults. In this sense, there is a growing number of studies that advance and support the inclusion of ST for strength, flexibility [4, 5] and balance [6, 7, 8] gains in older adults, and consequent functional improvement.

In fact, older adults experience impaired functional ability and self-efficacy over the years [9]. Thus, in addition to the physical benefits, the Center for Disease Control and Prevention (CDC) reinforces the importance of mechanisms which not only improve functionality but also the quality of life in older adults [10]. However, although quality of life is a multifaceted phenomenon, the self-efficacy and overall well-being of older adults are significantly influenced by physical activity. Improvement in cardiovascular and functional parameters promoted by the exercise gives older adults autonomy and well-being [9].

Mobility is one of the domains of quality of life, and has been significantly associated with physical exercise practice [11]. Older adults with less mobility and functional independence are less involved in exercises [11], suggesting that engaging in regular physical exercises like strength, balance and flexibility training is important for achieving higher quality of life (QoL) in older people. In this view, other studies involving ST have also shown significant effects to improve the well-being in this population [9, 12].

Traditional resistance training programs focus on developing strength gain and muscle mass to control the deleterious effects of sarcopenia in older adults. The insertion of unstable surfaces at strength training (ST $+$ US) has demonstrated a complementary alternative to traditional ST for strength and balance improvement in different populations [6].

Studies examining the effects of ST $+$ US in older adults have indicated superior outcomes regarding strength gain and balance when compared to control groups or traditional training [13, 14, 15, 16]. Despite the good results, these studies used protocols involving less than 12 weeks and applied isolated muscle exercises for the core or lower limbs. Furthermore, there is no information to date about the effects of this modality on flexibility and quality of life.

Considering the importance of strength training for maintenance and/or improvement of physical fitness components and QoL, the aim of this study was to evaluate the effect of a 24-week strength training protocol with and without unstable surfaces on the strength, flexibility and QoL in older adults.

2. Methods

2.1 Participants

Fifty-eight community-dwelling older women voluntarily participated in the study. Participants were eligible if they met the following criteria: 1) no severe functional limitation (e.g., several osteoarthritis); 2) no previous experience with strength exercises in the last six months; 3) no previous cardiovascular (e.g., ischemic heart disease), neurological (e.g., dementia), and other clinical conditions or signal/symptoms of unstable disease (e.g., angina pectoris) which contraindicate participation in an exercise program. The participants were recruited through local advertising, social media, and personal contact at community centers that offer services for older people. The study conforms with The Code of Ethics of the World Medical Association and it was approved by the local ethics committee of University of Pernambuco (C.A.A.E 35220014.1.0000.5207 – August 21, 2014) and prospectively registered at Brazilian Clinical Trials Platform (protocol number: RBR-7wcmd6) that relates to large, multi-factorial studies. All participants signed an informed consent form prior to baseline assessments.

Figure 1.

Flowchart of study timeline.

2.2 Sample size calculation

Since no previous studies had identical experimental design the parameters of the two most similar studies for sample size calculation [11, 12] were used along with the GPower 3.1 software. Effect sizes greater than 0.39 were reported for balance and functional outcomes in both studies. Thus, we considered the following parameters: repeated measures with within-between interaction: $\alpha=$ 0.05; power (1 – $\beta$ ) $=$ 0.80; effect size $=$ 0.39; number of groups $=$ 3; number of measures $=$ 3; and loss of 15%. The minimum sample required was set at 42 volunteers (14 per group).

2.3 Experimental design

This is a secondary analysis from a previous randomized controlled trial designed to examine the effects of strength training with unstable devices in older adults [17]. The study was carried out between May 2016 and March 2017 in Caruaru city, PE, Brazil, and had two enrollment periods for volunteers. First, 36 volunteers were randomly allocated into three groups (ST, ST $+$ US or control group). In the second entry, 22 volunteers were only randomized into the two experimental groups ( ST $+$ US and ST). Figure 1 displays the study timeline flowchart. From the 96 participants who did the screening, 58 provided written informed consent and were randomized into one of the three intervention groups. The randomization process was performed by a research assistant who was not involved in the study by generating random numbers using a computer software program. Participants were assessed for grip strength, flexibility and quality of life at baseline, 12-weeks (short-term) and after 24-weeks (long-term) of intervention. Blinding of the patients and therapists was not possible due to the type of exercise intervention. However, a trained assessor performed the data collection in each time-point for dependent variables in a blinding fashion.

2.4 Interventions

Participants who were assigned to traditional ST intervention performed moderate-intensity strength exercise, thrice weekly during 24-weeks. Exercise prescription and progression (external resistance adjustments) followed the American College of Sports Medicine (ACSM) recommendations [18] and consisted of whole-body exercises (leg press 45 ${}^{\circ}$ , horizontal dumbbell press, unilateral row with dumbbells, plank, abdominal and bridge). A linear periodization was adopted and the prescription ranged from two to five sets of 7–12 repetitions, with 60-s to 150-s recovery interval between the sets and exercises, respectively. Participants allocated to ST $+$ US group performed the same exercise training prescription of traditional ST, however unstable devices (i.e. BOSU ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}{\textregistered}}$ ball, balance disc and Swiss ball) were progressively included through the intervention in order to promote higher neuromotor challenge and proprioceptive demand. Further details of exercise training protocols are described in Fig. 2.

Figure 2.

Description of the strength training program and the instability levels progression.

Control group participants did not undergo any type of intervention, but they were encouraged to maintain their daily routine and lifestyle habits. At completion of intervention, a short-version of exercise training program was offered.

2.5 External resistance progression

We monitored the external resistance progression after 4-, 12- and 24-weeks of intervention in the following exercises: horizontal dumbbell chest press and unilateral row with dumbbell (trunk and upper limbs), and leg press 45 ${}^{\circ}$ (lower limbs). We considered the highest value recorded at completion of each time-point as a measure of external resistance (in kilograms).

2.6 Outcome measures

We used the handgrip test (in both hands), the sit-and-reach test (SRT) and the World Health Organization Quality-of-Life Scale (WHOQOL-BREF) to measure grip strength, flexibility and health-related quality of life, respectively.

The handgrip test was performed using an adjustable and calibrated dynamometer with a digital display (CAMRY, United States) with a scale from 0 to 100 kgf. Participants were evaluated sitting with the shoulder slightly adducted, the elbow flexed at 90 ${}^{\circ}$ and the forearm and wrist in a neutral position as recommended by the American Society of Hand Therapists [19]. Participants received required guidance and were familiarized with the equipment by performing light contractions. The positioning of the hands was adjusted, such the proximal interphalangeal joint of the hand was adjusted to allow the grip to be performed between the fingers and the thenar region with maximum comfort. After that, participants performed three attempts of a maximum voluntary isometric contraction for 5-s, with a 1-min rest interval between hands and, the highest value was recorded for analysis.

Table 1
General characteristics of participants

Variables	ST ( $n=$ 22)		ST $+$ US ( $n=$ 22)		Control ( $n=$ 14)		$p$ -value
Demographic
Age (years)	68.11	$\pm$ 3.89	66.94	$\pm$ 5.65	67.50	$\pm$ 4.75	0.767
Anthropometric
Body mass (kg)	64.89	$\pm$ 11.12	71.89	$\pm$ 12.81	69.88	$\pm$ 13.78	0.231
Stature (cm)	153.67	$\pm$ 5.35	155.74	$\pm$ 6.85	153.75	$\pm$ 4.81	0. 496
BMI (kg/m ${}^{2}$ )	27.55	$\pm$ 5.12	29.75	$\pm$ 5.69	29.59	$\pm$ 5.82	0.425

Note: BMI – Body mass index; Values are displayed as mean and standard deviation.

Figure 3.

Mean and standard error of the external resistance (in kilograms) after 4-, 12- and 24-weeks of intervention. Note: * Statistically different from baseline assessment ( $p<$ 0.05).

The SRT assesses lumbar and lower limb flexibility [20]. A wooden bench 48 cm long with a tape measure fixed (ruler) on it was used to perform the test. Each subject was positioned sitting on the floor with their legs stretched out straight ahead and feet placed flat against the box, bent forward with their palms facing downwards and sliding over the ruler. Participants performed three attempts and the highest value between them was recorded.

The brief version WHOQOL-BREF questionn-aire [21] was applied in a face-to-face interview. Briefly, WHOQOL-BREF have 26-items encompassing different domains including (overall quality of life – 2 items; physical health – 7 items; psychological health – 6 items; social relationship – 3-items; environmental health – 8 items). Each item of the WHOQOL-BREF is scored from 1 to 5 on a response scale and the total score were computed (higher scores denote higher quality of life).

2.7 Statistical analysis

All statistical procedures were followed the principles of intention-to-treat, such that all randomized participants were included to estimate intervention effects, irrespective of potential deviations from treatment protocol which they were originally assigned (e.g., loss of follow-up, non-compliance).

Firstly, we performed a descriptive analysis and visual inspections (e.g., Q-Q plot, histograms) to check data normality (or lack thereof). Within- and between-group differences and their respective 95% confidence intervals were calculated using linear mixed models by using group, time and group-versus-time interaction terms, as well as the Dunn-Sidak post hoc for multiple comparisons adjustments. The differences were considered statistically significant at $p<$ 0.05. The statistician was blinded for interventions and data analysis was processed using SPSS software version 20 (IBM SPSS Corporation, New York, USA).

3. Results

The descriptive characteristics of participants between experimental groups at baseline are shown in Table 1. There were no differences between groups at baseline with respect to demographic and anthropometric characteristics, and dependent variable measures ( $p>$ 0.05).

A similar improvement was observed regarding the external resistance of trunk and upper limbs, and lower limbs in both exercise groups during all intervention ( $p<$ 0.05) (Fig. 2). Descriptive results of the outcomes at baseline, 12 and 24 weeks between groups are shown in Table 2. In addition, the results of within- and between-groups differences of the effects of traditional ST and ST $+$ US on dependent variables are presented in Table 3.

Significant within-group changes (24-weeks – baseline) in grip strength were observed for all groups (Right hand: ST: $p<$ 0.001; ST $+$ US: $p=$ 0.006; control: $p=$ 0.023; Left hand: ST $p<$ 0.016; ST $+$ US: $p=$ 0.048; control: $p=$ 0.001). At completion of 24-weeks, no between-group differences ( $p>$ 0.05): were observed for grip strength.

The ST $+$ US ( $p=$ 0.023) and ST ( $p=$ 0.003) groups improved the SRT scores, with no significant changes in control after 24-weeks of intervention. Compared with control, a significant between-group difference was observed only for ST group at the end of intervention [ $+$ 6.19 (95% CI 1.31 to 11.07), $p=$ 0.006].

Regarding WHOQOL-BREF scores, both exercise groups experienced significant improvements through of 24-weeks, and these gains were superior to the control group at the end of intervention [ ST $+$ US: $+$ 15.11 (95% CI 7.28 to 22.94), $p<$ 0.001; and ST: $+$ 9.94 (95% CI 1.12 to 18.76), $p<$ 0.001]. No inter-group differences were found.

Table 2
Descriptive results (mean $\pm$ standard deviation) of the effects of 24-weeks of traditional ST and ST+US on grip strength, flexibility and quality of life in older women

	Strength training (n=22)						Unstable strength training ( $n=$ 22)						Control ( $n=$ 14)
	Initial		Middle		Final		Initial		Middle		Final		Initial		Middle		Final
Grip strength right hand (kgf)	22.58	$\pm$ 7.54	23.68*	$\pm$ 5.89	25.29*	$\pm$ 6.15	25.06	$\pm$ 5.10	27.00	$\pm$ 4.74	27.21*	$\pm$ 5.25	24.35	$\pm$ 3.89	25.36	$\pm$ 3.65	26.14*	$\pm$ 3.74
Grip strength left hand (kgf)	20.74	$\pm$ 6.54	22.61*	$\pm$ 6.13	23.40*	$\pm$ 6.86	24.41	$\pm$ 4.52	24.14	$\pm$ 4.56	25.07*	$\pm$ 4.34	21.64	$\pm$ 3.92	22.43	$\pm$ 2.44	23.50*	$\pm$ 2.85
SRT (cm)	22.50	$\pm$ 9.13	24.64	$\pm$ 6.56	27.21*#	$\pm$ 6.08	20.82	$\pm$ 10.19	22.92	$\pm$ 9.96	23.76*	$\pm$ 10.15	21.29	$\pm$ 6.58	22.36	$\pm$ 7.06	20.93	$\pm$ 4.55
WHOQOL (score)	100.89	$\pm$ 15.36	110.76*#	$\pm$ 11.76	109.53*#	$\pm$ 11.05	96.41	$\pm$ 9.27	105.00*#	$\pm$ 10.04	112.94*#	$\pm$ 6.49	95.71	$\pm$ 12.11	96.21	$\pm$ 9.76	97.36	$\pm$ 11.11

Note: SRT – Sit-and-reach test; WHOQOL – World Health Organization Quality of Life; Values showed as mean and standard deviation. * – represents a statistical difference compared to the baseline; # – Represents difference compared to the control group ( $p<$ 0.05).

Table 3

The mean differences within- and between-groups with 95% confidence intervals of the Linear Mixed Models

	Grip strength – right		Grip strength – left		SRT		WHOQOL-BREF
Within-groups
Week 12 – Week 0 (short-term)
ST ( $n=$ 25)	1.71	( $-$ 0.18 to 2.38)	1.86	(0.45 to 3.28)	2.14	( $-$ 1.49 to 5.77)	9.71	(2.70 to 16.71)
ST $+$ US ( $n=$ 25)	1.94	(0.59 to 3.30)	$-$ 0.27	( $-$ 1.77 to 1.22)	2.10	( $-$ 1.74 to 5.94)	8.59	(1.18 to 15.99)
CG ( $n=$ 14)	1.00	( $-$ 0.47 to 2.47)	0.79	( $-$ 0.48 to 2.06)	1.07	( $-$ 0.34 to 2.48)	0.50	( $-$ 3.56 to 4.56)
Week 24 – Week 0 (long-term)
ST ( $n=$ 25)	2.71	(1.22 to 4.19)	2.66	(0.96 to 4.37)	4.71	(0.74 to 8.68)	8.63	(1.58 to 15.68)
ST $+$ US ( $n=$ 25)	2.15	(0.58 to 3.73)	0.66	(0.07 to 2.87)	2.94	(0.25 to 7.13)	16.53	(9.07 to 23.99)
CG ( $n=$ 14)	1.78	(0.25 to 3.32)	1.86	(0.74 to 2.97)	$-$ 0.36	( $-$ 5.63 to 4.91)	1.64	( $-$ 7.29 to 10.57)
Between-groups
Week 12 (short-term)
ST – CG	$-$ 0.15	( $-$ 1.90 to 1.60)	0.96	( $-$ 1.15 to 3.10)	1.42	( $-$ 2.99 to 5.83)	11.72	(4.01 to 19.42)
ST $+$ US – CG	1.04	( $-$ 0.74 to 2.83)	$-$ 0.67	( $-$ 2.85 to 1.51)	0.89	( $-$ 3.62 to 5.44)	8.43	(0.58 to 16.28)
ST $+$ US – ST	1.20	( $-$ 0.46 to 2.86)	$-$ 1.62	( $-$ 3.67 to .42)	$-$ 0.40	( $-$ 3.77 to 2.96)	$-$ 3.29	( $-$ 10.58 to 4.00)
Week 24 (long-term)
ST – CG	0.70	( $-$ 1.08 to 2.42)	0.68	( $-$ 1.43 to 2.78)	5.42	(1.01 to 9.83)	9.50	(1.80 to 17.20)
ST $+$ US – CG	0.47	( $-$ 1.32 to 2.25)	$-$ 0.81	( $-$ 2.99 to 1.37)	3.16	( $-$ 1.35 to 7.68)	15.23	(7.37 to 23.08)
ST $+$ US – ST	$-$ 0.21	( $-$ 1.46 to 1.87)	$-$ 1.48	( $-$ 3.53 to .56)	$-$ 2.26	( $-$ 6.44 to 1.93)	5.72	( $-$ 1.57 to 13.05)
Note: SRT – Sit and reach test; WHOQOL-BREF – World Health Organization Quality of Life. Significant results are highlighted in grey background cells ( $p<$ 0.05).

4. Discussion

Our main findings showed that 1) traditional ST and ST $+$ UST were effective to improve health-related quality of life among community-dwelling older women; 2) only traditional ST protocol improved flexibility levels at completion of intervention; and 3) no between-group differences were observed for grip strength at completion of intervention, suggesting that both exercise regimes were not effective to improve grip strength.

The health-related quality of life might be perceived from subjective and multidimensional aspects (physical well-being, functional capacity, emotional well-being, social well-being) [22]. From this perspective, lifestyle-based therapies such as physical activity and exercise have beneficial effects in several domains of quality of life across the lifespan, including aging [6]. Herein, we demonstrated improvements on overall WHOQOL-BREF score after 24-weeks of traditional ST and ST $+$ US programs in older women, which are in accordance with previous trials [23, 24, 25]. A possible explanation might be associated with the notion that strength exercise with and without balance components are known to be effective strategies to improve musculoskeletal fitness, socialization, well-being and other important components of quality of life. Thus, evidence-based decision-making needs to be stimulated in clinical practice to recommend both exercise-based approaches in order to promote better quality of life of older women.

Flexibility gains in our study were only demonstrated after ST intervention. A previous systematic review led by Correia et al. [4] showed that older adults undergoing traditional ST programs improved flexibility levels. This finding has implications considering the morphological and functional impact of aging process on muscular, bone and joint components which may lead clinically reductions of range of motion. On the other hand, we did not observe between-group differences on flexibility among individuals allocated to ST $+$ US. To our knowledge, this is the first study to analyze the effects of ST $+$ US on flexibility measured by the sit-and-reach test. A possible difference between exercise strategies might be partly explained by Bernstein’s theory [26]. The theory states that there is a natural freezing on the articular degrees of freedom in the movement acquisition process. Regarding ST $+$ US, a neuromotor complex strategy, there is always a new and constant challenge in order to add difficulty to the movement itself, and so it is natural that subjects freeze range of motion impairing flexibility gains. Future studies are warranted regarding this issue.

As expected, we found overall muscle strength gains (measured by external resistance) after moderate-intensity ST intervention, which agree with previous studies that investigated the effects of strength training regimes in older adults [13, 27]. We observed that combined strength exercise with unstable devices was also effective to induce similar gains in this outcome. Last but not least, our findings showed grip strength gains in all interventions. This result it is not surprising because although the strength exercise interventions are powerful to improve muscular components in older adults, our exercise-based prescription was not proposed to improve a specific manifestation of strength. We designed an exercise protocol focused on main muscular clusters according to ACSM recommendations.

Although we used a 24-week randomized controlled trial to assess the effects of strength training with and without instability in the elderly, our study has weaknesses and limitations that deserve to be highlighted. Of note, our study sample consisted exclusively of older women living independently in the community who were without significant physical and cognitive impairments or any overt disease. Thus, the current results may not generalize to older men or individuals with significant physical and/or cognitive impairments.

5. Conclusion

Our findings suggest that traditional strength exercises were effective for improving flexibility and health-related quality of life among healthy older women. Combining unstable devices with traditional exercise did not provided additional gains in order to promote these traits.

Author contributions

CONCEPTION: Rodrigo Cappato de Araújo.

PERFORMANCE OF WORK: André Luiz Torres Pirauá, Valéria Mayaly Alves de Oliveira and Natália Barros Beltrão.

INTERPRETATION OR ANALYSIS OF DATA: André Luiz Torres Pirauá, Valéria Mayaly Alves de Oliveira and Bruno Remígio Cavalcanti.

PREPARATION OF THE MANUSCRIPT: André Luiz Torres Pirauá and Bruno Remígio Cavalcanti.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Ana Carolina Rodarti Pitangui and Rodrigo Cappato de Araújo.

SUPERVISION: Rodrigo Cappato de Araújo.

Ethical considerations

The study conforms with The Code of Ethics of the World Medical Association and it was approved by the local ethics committee of University of Pernambuco (C.A.A.E 35220014.1.0000.5207 – August 21, 2014) and prospectively registered at Brazilian Clinical Trials Platform (protocol number: RBR-7wcmd6) that relates to large, multi-factorial studies. All participants signed an informed consent form prior to baseline assessments.

Funding

This study was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (457585/2014-5) and Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco – FACEPE (APQ-0580-4.08/14).

Footnotes

Acknowledgments

We thank the participants for their contribution to the study. We thank the CNPq and FACEPE for the financial support to carry out this study.

Conflict of interest

The authors declare no conflicts of interest.

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