Affective response of postmenopausal women to resistance training on stable and unstable surfaces: a randomized cross-over study

Respostas afetivas de mulheres pós-menopausadas submetidas ao treinamento com pesos em superfície estável e instável: um estudo cross-over randomizado

Danielle Cristhiane de Lira daniellelira91@gmail.com

Universidade Federal Rural de Pernambuco, Brazil

Juliana Daniele de Araújo Silva

Universidade Federal de Pernambuco, Brazil

Fernando Damasceno de Albuquerque Angelo

Universidade Federal de Pernambuco, Brazil

Rodrigo Ramalho Aniceto

Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Norte, Brazil

Breno Quintella Farah

Universidade Federal Rural de Pernambuco, Brazil

André Luiz Torres Pirauá

Universidade Federal Rural de Pernambuco, Brazil

Regular exercise has been recommended for improving the health level and quality of life of the Brazilian population. For adults, the Ministry of Health recommends 150 minutes of moderate physical activity or 75 minutes of vigorous activity per week to obtain health benefits, such as preventing and/or reducing mortality from chronic diseases and reducing weight, stress, and anxiety and depression symptoms.1

However, more than a quarter of the world’s adult population (1.4 billion) is insufficiently active. In high-income countries 26% of men and 35% of women are considered insufficiently active, while in low-income countries 12% of men and 24% of women are considered insufficiently active.2

Among exercise-related factors, there is a positive relationship between feeling pleasure during physical activity and habitual engagement.3 Exercise programs could be modified to add a greater feeling of pleasure, thus ensuring adherence and, consequently, improved health indicators. Given that resistance training effectively increases muscle strength4 and several other parameters linked to health and functional autonomy,5 the impact of affective response on resistance training has been investigated.

There is evidence that changing the intensity of resistance exercises does not affect the sensation of pleasure, and it can even reduce pleasure when performed until voluntary failure.6 No differences in perceived effort and pleasure scores could be found between traditional resistance training methods and cluster sets.7 However, studies on the use of unstable surfaces in resistance training are still scarce.

According to the literature, adding instability to resistance training can promote simultaneous gains in balance and muscle strength that are superior to traditional methods8,9 and it can reduce the fear of falling.10 This is because the imbalance produced by unstable surfaces is a greater challenge for the neuromuscular system, requiring adaptation and stabilization during movement.11,12 The increased neuromuscular demand is due to proprioceptive stimulation through sensory input from mechanoreceptors in muscles, joint capsules, tendons, ligaments and skin.13

In view of the above, it is important to determine whether adding instability to resistance training, which can provide additional benefits to traditional resistance training,8,9,14,15 produces displeasure due to the increased exercise complexity, ie, the need for strength and balance at the same time. The results may be important for interventions to maintain functional capacity, especially in post-menopausal women, who suffer from physiological changes that can influence affective responses to training, such as muscle fatigue, sleep-wake cycle disorders, chronic or persistent pain, and the harmful effects of premature aging.16 Therefore, the objective of this study was to compare affective response in postmenopausal women who underwent 6 weeks of resistance training on stable and unstable surfaces.

This quasi-experimental randomized counterbalanced cross-over study of postmenopausal women was approved by the Universidade Federal Rural de Pernambuco Research Ethics Committee (number 35220014.1.0000.5207). All procedures adhered to national legislation and the Declaration of Helsinki.

The sample included postmenopausal women between 50 and 60 years old. The age group restriction was intended to create a minimally homogeneous sample, excluding women with premature menopause and those of advanced age. Menopause was considered a minimum of 12 months without menstruation or the use of hormonal contraceptives.17 Exclusion criteria consisted of injury during the intervention, regardless of the nature, and inability to continue participating for any declared reason (eg, moving to another city or personal/family problems).

The study was conducted between February and May 2019. Eligible participants underwent an initial assessment consisting of anamnesis, collection of personal data (name, date of birth, date of last menstrual period, date of last hormonal contraceptive use), history of regular exercise (types and length of training in weeks/months/years), anthropometric data (weight, height and body mass index), and history of injuries and chronic diseases. After being informed about the risks and benefits of this research, the volunteers provided written informed consent to participate.

Before data collection, the researchers underwent the training protocol to ensure methodological rigor, in addition to evaluating the feasibility of methodological and operational procedures. The study took place in 2 stages: in the first, which lasted 2 weeks, the participants adapted to exercises in both the stable and unstable protocols. They were then allocated to a single experimental condition. The second stage consisted of 3 weeks of intervention in the allocated condition. At this stage, affective response data on the stable and unstable exercise protocols were collected (Figure 1).

FIGURE 1
Infographic of the experimental design.

The training consisted of 8 exercises involving the lower and upper limbs and trunk. In the adaptation stage, there were 2 series of 7 or 8 repetitions for each exercise, with a 60- to 90-second recovery interval, while in the intervention stage this was increased to 3 series of 8 to 10 repetitions, maintaining the same recovery interval. At the end of the third week of the intervention, the experimental conditions were reversed for another 3 weeks. Both experimental conditions strictly followed the same volume, intensity, recovery intervals, and weekly frequency, differing only by adding unstable surfaces to the exercises, which are shown in Box 1. Affective response data were collected using the Hardy and Rejeski Sensation Scale (1989) at the end of each week of the intervention.18 The scale was applied after the end of the last series of each exercise and 10 minutes after the end of the session. This instrument is an 11-point scale, with responses ranging from +5 to 5 and verbal descriptors for all odd numbers and 0: +5 (“very good”); +3 (“good”); +1 (“reasonably good”); 0 (“neutral”); 1 (“fairly bad”); 3 (“bad”); 5 (“very bad”). Positive numbers represent pleasure (positive affect) and negative numbers represent displeasure (negative affect). Previous studies have recommended this scale to measure affective response during exercise and to verify adherence to training/intervention programs.19,20

BOX 1
Description of exercises involving unstable surfaces, including the device and the supported body region.

The data were processed and analyzed using IBM SPSS Statistics 20.0 (IBM, Armonk, NY, USA), Statistica for Windows 5.1 (StatSoft Inc., Minneapolis, MN USA), and GraphPad Prism 5.03 (GraphPad Software, Inc., Boston, MA, USA) Affective response, globally and for each exercise, in the first and last weeks were compared using the Wilcoxon test. For all statistical analyses, p < 0.05 was considered significant. The data are presented as median and interquartile range.

Of the 30 initial volunteers, 14 completed the study (Figure 2). Some dropouts were due to changes in address, work hours, other uninformed personal reasons, or pre-existing health conditions. The study included 14 postmenopausal women (55.00 [SD, 3.00] years; height 1.55 [SD, 0.03] m; body mass 78.70 [SD, 12.00] kg; and body mass index 32.80 [SD, 4.90] kg/m).

FIGURE 2
Participant flowchart.

Surface type did not influence affective response at the end of the sessions or between the first and last weeks of the intervention (stable surface: median (interquartile range [IQR] 5.00 [3.00]; unstable surface: median [IQR] 5.00 [1.00]; p = 0.114). Positive affect predominated in both conditions; negative affect was only reported in the stable condition (7.14%). A significant difference in affect was only observed for the bridge exercise (Table 1).

TABLE 1
Comparison of affective response in the first and last week of the stable and unstable exercise conditions, considering the final series of each exercise.

Values expressed as median (interquartile range); data analyzed using the Wilcoxon test; *statistically significant difference.

Adding unstable surfaces to resistance training did not negatively impact the affective response of the participants. In general, affective response at the end of the sessions and in the intra-exercise comparison varied between “pleasant” and “very pleasant”. It should be pointed out that the responses were similar in all tested conditions.

One possible explanation for this similarity is that the sessions were supervised by the researchers.21 Supervision may have increased the participants’ perceived safety level during the unstable exercises. Thus, contrary to expectations, the greater neuromuscular demand under these conditions22 was not considered sufficiently problematic to produce displeasure.

Affect was also similar among the individual exercises in both conditions, except the bridge exercise. For this exercise, participants had to remain in a static position with their torso suspended while raising their hips and supporting their feet on a balance disc. However, even given the complexity of the task, instability increased the perception of pleasure. One explanation for this could be perceived self-efficacy, ie, when people feel more capable, they tend to perform tasks with greater ease and motivation,23 which reinforces the idea that unstable surface conditions increase affect.

Considering that affective response was similar across conditions, it may be assumed that adherence to resistance training will also be similar with or without unstable surface conditions during training sessions. Thus, unstable surfaces can be incorporated into resistance training without compromising affective response in short-term interventions.

A systematic review24 of 94 clinical trials (9821 older adults) involving different exercise interventions found balance improvement in only 11 of 22 trials involving resistance training. The authors concluded that resistance training alone may not lead to significant balance gains in older adults.

It is possible that adding unstable surfaces to resistance training can improve balance, considering that resistance training is not very effective for this purpose. For example, benefits in muscle strength, balance, and apprehension about falling have been observed in other studies that compared instability training with resistance training on a stable surface.8,9,10 The main difference was that unstable surfaces stimulate proprioception by increasing neuromuscular demand.13 However, the unpredictable movements involved in training on unstable surfaces can pose a risk to joints.25

This study involves some limitations, including:

1. 1. the small number of participants who completed the protocol, which made more robust statistical analysis and, consequently, extrapolation of the results unfeasible;
2. 2. the short study training protocols, which could have been extended for additional weeks;
3. 3. the lack of a washout period between interventions;
4. 4. we did not control for medication use, sleep status, mood, or other variables that could have influenced the results.

However, the strength of this study is that it is the first to investigate affective response to a resistance training intervention involving unstable surfaces.

As a practical application, resistance training involving unstable surfaces does not lead to discomfort in post-menopausal women, which may improve adherence to training regimens and promote benefits, such as greater balance and coordination and a lower risk of injury due to increased proprioception, motor skills, and intra- and intermuscular coordination. 25 In terms of scientific advancement, this study increases the feasibility of research on strength training on unstable surfaces among older adults and its potential psychometric benefits.

Finally, future studies can focus on how affective response can positively or negatively influence regular exercise programs.

Including instability in resistance training did not negatively impact affective response in postmenopausal women at the end of the sessions. Although instability increased perceived pleasure in the bridge exercise, a more robust analysis is needed to clarify the relationship between resistance exercises involving unstable surfaces and perceived pleasure in postmenopausal women.