Effects of weight-bearing dance aerobics on lower limb muscle morphology, strength and functional fitness in older women

Participants

Thirty-seven older women were recruited through advertising posters in the community and online platforms in the Yangpu and Hongkou districts of Shanghai. During the first appointment, questionnaires were completed by the participants, which included the physical activity readiness questionnaire (PAR-Q) for pre-screening, the adapted version of the international physical activity questionnaire-short form (IPAQ-SF) to assess physical activity, including sedentary behavior (SB), light physical activity (LPA), moderate and vigorous physical activity (MVPA), total physical activity (TPA), and included the intake of calcium supplements and vitamin D. We enrolled all participants who met the following inclusion criteria: 1) women aged 60–75 years old; 2) a relatively low amount of physical activity (in the past 3 months, moderate-to-vigorous exercise less than three times weekly with a session lasting less than 30 min); 3) those who participated voluntarily and signed informed consent. The exclusion criteria were as follows: 1) individuals with any potential health risks associated with exercise (confirmed by PAR-Q) or advised against participating by medical professionals; 2) those with severe diseases, such as severe heart disease, diabetic neuropathy respiratory disease, orthopedic conditions, post-surgical recovery, unstable blood pressure, or other conditions which prevented them from completing the exercise and physical fitness test.

All participants signed informed consent. The study was approved by the Ethics Committee of Shanghai University of Sport (ethic committee code: 102772020RT096), and registered by the China Clinical Trials Center (ChiCTR2100047187).

Intervention

Thirty-seven participants were divided into two groups based on their preference, with 20 participants in the intervention group, and 17 in the control group. Participants in the intervention group performed 12 weeks WBDA three times a week, each session 90 min, including 10 min of warm-up, 60 min of exercise, 10-min stretching, and two 5-min rest periods. The music accompanied the exercise routine set at approximately 130 beats per minute. The subjects were engaged in dance aerobics, including but not limited to march, walk, easy walk, mambo, V-step, grapevine, step touch, leg curl, and knee lift-up.

All participants wore a weighted vest, net weight 750 g, and the vest pockets were loaded with 150 g lead plates prescribed as a percentage of their body weight. Participants were freely acquainted with dance aerobics (DA) in the first week without load. Subsequently, the load was systematically increased, as listed in Table 1.

To adjust the intensity of exercise promptly and to prevent potential accidents, subjects wore a heart rate monitor (Polar OH1) to monitor the real-time heart rate. Exercise intensity was formulated as 60–75% of the maximum heart rate (Pescatello, 1999), where age-predicted maximum heart rate = 220–age.

Measurements

Statistical analysis

Independent samples t-test was performed to determine the differences at baseline. The paired-sample t-test was used to determine the differences between the participants’ pre- and post-intervention muscle morphology, strength and functional fitness. Effect size, Cohen’s d, was calculated and categorized as small (0.2 ≤ Cohen’s d < 0.5), medium (0.5 ≤ Cohen’s d < 0.8), or large (Cohen’s d ≥ 0.8) effect sizes (Cohen, 1988).

With pre-test data as a covariate, ANCOVA was employed to compare inter-group differences. Effect size, partial η², defines small, medium, and large effect sizes as 0.01, 0.06, and 0.14 (Cohen, 1992). If the date violated the normal distribution (tested by the Shapiro-Wilk test), or had an interaction effect between the group and the baseline, the Mann-Whitney U test was used to analyze the effects of 12 weeks WBDA. The effect size (r) was calculated by dividing the Z-score by the square root of N, indicating a large effect size using Cohen’s d criteria of 0.10, 0.30, and 0.50 to define small, medium, and large effect sizes, respectively (Rosenthal, 1994).

All statistical analyses were conducted using SPSS (version 26.0), with significant differences at P < 0.05 and borderline significance at 0.05 < P < 0.1.

Basic information

Among 37 recruited participants, two participants from each intervention and control group withdrew due to poor transportation and inability to train consistently. Thirty-three participants were included in the statistical analysis, with 18 in the intervention and 15 in the control group. The experimental process is shown in Fig. 1. Apart from age, no significant differences were observed between the two groups regarding height, weight, BMI, duration of menopause, and age at menopause. There were also no significant group differences in ST, TPA, LPA, or MVPA (Table S1). An overall compliance rate of 89.19% was observed, with the intervention group having a 90% compliance rate. The attendance rate of the intervention group was 95.99%. The average heart rate in the intervention group was 112.5 beats per minute, representing approximately 72% of the maximum heart rate (Table 2).

The effects on muscle morphology

The morphological results of the knee extensor and flexor muscles are shown in Table 3. Compared to baseline values, after 12 weeks of intervention, the thickness of VI and quadriceps in the intervention group increased by 0.27 ± 0.44 cm (P = 0.02) and 0.40 ± 0.61 cm (P = 0.01), respectively. The RF had a trend of thickening (Cohen’s d = 0.41, P = 0.095), with a reducing trend in RF pennation angle (Cohen’s d = 0.42, P = 0.09). In contrast, the control group displayed a potential decline in the thickness of VI at the end of the 12-week duration (Cohen’s d = 0.48, P = 0.09).

Moreover, compared to the control group, the VI and quadriceps thickness in the intervention group increased (F = 17.85, P < 0.01, partial η² = 0.37 and F = 15.62, P < 0.01, partial η² = 0.34), with a marginally significant increase in the thickness of soleus (F = 3.59, P = 0.07, partial η² = 0.11).

However, no significant difference was observed between the groups regarding the thickness of RF, soleus, GL and GM, the length of all muscle fibers and the pennation angle.

The effects on muscle strength

The results of isokinetic muscle strength of the knee extensor and flexor muscles are shown in Table 4. The results indicated that after 12 weeks of intervention, the peak torque of knee flexors in the intervention group increased by 5.54 ± 4.81 Nm/kg compared with the pre-test, accompanied by a noteworthy increase in the peak torque/body weight ratio of 0.06 ± 0.10 Nm/kg. Furthermore, the knee peak torque flexors/extensors significantly increased by 7.21 ± 10.43%. Conversely, no significant changes were observed in the control group.

Upon accounting for baseline differences (P = 0.02) through ANCOVA, a significant increase was observed in the intervention group in terms of flexors peak torque/body weight ratio after the 12-week intervention, in comparison to the control group (F = 4.47, P = 0.04, partial η² = 0.13).

The effects on functional fitness

The results of functional fitness tests are shown in Table 4. The results showed that the SCST in the intervention group increased by 3.91 ± 5.35 s (P < 0.01) after 12 weeks of intervention, which was significantly higher than that in the control group (z = −2.16, P = 0.04).

Although the 30 s CST in the intervention group tended to increase (Cohen’s d = 0.46, P = 0.07), a similar significant increase was observed in the control group (P < 0.01); thus, there was no significant difference between the two groups.

Muscle morphology

Muscle strength

Previous studies have demonstrated that physical activity can increase muscle strength and balance, while significantly reducing the risk of falls and fractures (Stevens & Olson, 2000). Moreover, consistent participation in low-impact aerobic walking exercises can significantly improve knee extension torque among active individuals compared with their sedentary counterparts (Wen et al., 2017; Yang et al., 2022). After the 12-week intervention, no significant change in the knee extension torque was observed in the intervention group. However, the peak torque/weight ratio of knee flexors in the intervention group was significantly improved compared to the control group, consistent with previous studies, indicating that a combination of aerobic and resistance exercises enhances knee muscle strength.

After 12 weeks of intervention, the flexors peak torque/extensors peak torque (H: Q) in the intervention group increased from 0.57 to 0.64. The typical H: Q ratio is approximately 0.6 for individuals without musculoskeletal issues, which tends to decline with age. A lower H: Q ratio may indicate an imbalance in lower limb muscle strength and the occurrence of leg injury (Evangelidis et al., 2016). The increased H: Q observed in this study might be associated with increased knee flexion torque. It could be due to the great involvement of the quadriceps in WBDA. To maintain dynamic balance, aid ligaments in preserving joint stability, and ensure even distribution of pressure across the knee joint, the engagement of the quadriceps activates the hamstrings, thus increasing hamstring torque (Baratta et al., 1988).

Functional fitness

Functional fitness is the ability of the human body to perform daily activities independently and safely without fatigue (Rikli & Jones, 1999). Enhanced functional fitness is associated with lower abdominal fat (Chen et al., 2020) and health-related quality of life in older adults (Chung et al., 2017).

One-leg standing is a standard balance indicator, with eyes open or closed in two states. Previous studies have shown that patients unable to sustain one-legged balance for 5 s with their eyes closed are 2.1 times more likely to fall than those who can maintain balance for more than 5 s (Vellas et al., 1997). Additionally, the time spent on SCST was negatively correlated with somatic symptoms and anxiety/insomnia (Hayashi et al., 2002). The SCST can enhance the arterial resilience of the supporting leg (Zhou et al., 2022), thereby fostering cardiovascular well-being and preventing cardiovascular diseases in older women. These dual benefits represent the significance of SCST as an indicator of balance ability and a predictive measure of fall susceptibility, thus reflecting the overall health status. Significant improvements were observed in SCST following the 12-week intervention, consistent with previous findings (FilipoviĆ et al., 2021; Vogler et al., 2009). Notably, before the intervention, the majority (56%) of participants in the intervention group exhibited SCST durations of less than 5 s, which substantially decreased to 28% after the intervention. Conversely, the control group witnessed an increase in individuals with sub-5-s SCST from 47 to 53%. It highlights that 12-week WBDA can improve static balance in older women and potentially reduce the risk of falls and fractures.

The improvements of 30 s CST were observed in both the intervention and control groups, consistent with previous findings published in the literature (Marques et al., 2011). It may be related to sleep quality, mental state and other factors during testing. Nutrition, like dietary protein (Mareschal et al., 2020), was also proven to benefit function fitness.

In contrast to previous studies, this study did not yield evidence of WBDA leading to improvement in the 2-min step test and TUG, which could be attributed to prior studies involving frail subjects or older adults suffering from knee osteoarthritis. Notably, the older women in this study who were in better physical condition had greater physical function. Achieving more significant improvement in physical performance could necessitate an extended intervention period (>16 weeks) and more exercise.

Compliance and attendance rate

Compliance is closely related to the effect of intervention (Ariza et al., 2019). This study combined weight-bearing exercise and dance aerobics, yielding an impressive overall compliance rate of 89.19%. Notably, the intervention group exhibited an even higher compliance rate of 90%, surpassing the compliance rates of previous weight-bearing exercise studies (80.4% (Kim et al., 2018) and 84% (Winters-Stone et al., 2014), respectively). Compared with the attendance rates of 79.7% and 83% in other combined exercise studies using weight-bearing vests, a higher attendance rate of 95.99% was observed in this study. These compliance and attendance outcomes underscore that WBDA was more readily accepted by older women, thereby amplifying the feasibility of the study. The compliance and attendance rates in exercise interventions are pivotal in ensuring the precision and credibility of experimental outcomes. Therefore, future studies should attach importance to their potential implications on results.

Limitations

This study had certain limitations that should be acknowledged. Firstly, as the research was carried out during the COVID-19 pandemic, recruiting participants was challenging, resulting in a small sample size. In the future, we will expand the sample size to enhance the reliability and accuracy of our results. Secondly, participants may not prefer to stay with groups during the COVID -19 pandemic. Therefore, they were divided into groups according to their preferences, potentially introducing a significant risk of bias. Finally, the participants were all older women, which restricts the generalizability of the findings to other age groups or sexes. For further studies, broadening the study population to include men aged 60–75 years could provide insights into the impact of WBDA on the lower limb muscles of older adults.