Effects of Simultaneous Balance and Resistance Training in Older Adults
Condition: Muscle Weakness
MeSH terms: Muscle Weakness
Study type: Interventional

Summary: 
      Aging results in a gradual decline of physical abilities and consequently in functional
      impairments which increases the risk of falls in elderly people. It has been shown, that
      balance and resistance training can counteract the effects of aging. The aim of this study
      was to investigate effects of instability resistance training (IRT), combining balance and
      resistance training, on measures of muscle strength / power and balance for falls in healthy
      community-dwelling older adults. Therefore 75 elderly people, aged 65 - 80 years (Mage =
      70.4; SD = 4.3 years) were assigned into three intervention groups: machine-based (M-RT),
      machine-based instability (M-IRT), free weight instability resistance training (F-IRT). All
      three groups exercised over 10-weeks with two training sessions per week. Assessment of
      muscle strength (e.g. maximal isometric leg extension strength), power (e.g. chair rise test)
      and balance (e.g. gait, functional reach test) was conducted before and after training.

      Based on the principle of training specificity, it is assumed, that groups to improve better
      within their respective training modality. Thus, the investigators hypothesis that regarding
      measures of strength and power, M-RT performs better than M-IRT, performs better than F-IRT.
      As to measures of balance, we hypothesis that F-IRT performs better that M-IRT, performs
      better than M-RT.
    

Detailed description: 
      Background:

      In the course of aging, physical abilities gradually decline. Even though the cause of falls
      is assumed to be multifactorial, loss in muscle strength and balance control seems to be the
      most crucial intrinsic risk factors for falls.

      Several meta-analysis and reviews emphasise positive effects of resistance, balance and
      combined exercise interventions on measure of strength, power and balance performance and
      thus on intrinsic (i.e., person-related) risk factors for falls. Pure balance as well as pure
      resistance training have been effective in improving postural control (e.g., gait measures,
      leg extension strength) and reducing risk of falling in elderly people. Combined resistance
      and balance training describes in general a sequential or concurrent training program, where
      resistance and balance exercises are executed in a consecutive order within the same training
      session. These exercise interventions have shown positive effects as well. Merging resistance
      and balance training, executing both simultaneously has not been investigated in regard to
      fall prevention in elderly people yet.

      In the past 15 years, research of simultaneous resistance and balance training, so called
      'instability resistance training' (IRT), has been grown. IRT utilises unstable devices (Swiss
      balls, BOSU® balls, wobble boards, etc.) and an external load (e.g., weights). This training
      modality has shown to affect core and lower limb muscle activation positively, improving
      balance and further having comparable gains in measures of strength analogue to traditional
      resistance training. Kibele and Behm, for example, found superior improvements in the single
      leg hop following an IRT in healthy young adults. They concluded in line with the principle
      of training specificity, that IRT induced higher balance adaptions, which were prominent in
      the balance demanding singe leg hop. Further, Behm and Colado recommended IRT for elderly
      people and there are studies investigating effects of different kinds of IRT on older adults.
      Granacher and colleagues examined effects of core instability strength training (CIT) on
      measures of trunk muscle strength, spinal mobility, dynamic balance and functional mobility
      in older adults. They found meaningful improvements in measures of strength, balance and
      mobility in comparison to a control group. Another study, investigating effects of a swiss
      ball exercise program on older adults, found positive effects on measures of physical fitness
      and balance in comparison to a control group. Based on used exercises, these studies focused
      on strengthening the core and improving mainly balance abilities. In a slightly different
      approach to improve balance in older women, Chulvi-Medrano and colleagues utilized a
      lower-limb training program using a unstable T-Bow® device. The training group improved in
      measures of dynamic, static and overall balance, whereas the control group experienced a
      decline or no change in balance abilities. All three aforementioned studies utilised unstable
      devices but none incorporated additional loads within their training programs, hence the
      resistance component of IRT is limited to bodyweight. Hence, there is a lack of literature
      supporting evidence for feasibility and effectiveness of IRT incorporating additional load as
      resistance to improve measures of strength, power and balance in elderly people.

      To the investigators knowledge, no study has been conducted yet, investigating effects of IRT
      with additional load as resistance on risk factors for falls for elderly people.

      Measures:

      Data was acquired in our biomechanics laboratory. Questionnaires were completed in separated
      rooms. All tests were conducted and explained, using standardised verbal instructions
      regarding the test procedure to maintain equal treatment for all participants. A single
      assessment lasted 90 min per participant.

      Strength / power assessment:

      Well established clinical and biomechanical tests were administered to measure primary
      outcomes in muscle strength and power. In accordance with the recommendations of Granacher et
      al. strength assessments were performed after balance assessments to reduce interfering
      effects of muscle fatigue. Further, strength and balance tests were administered in a random
      order within their respective block. One practice trial was provided for every test. Test
      procedures were conducted according to the recommendations of Gschwind et al. if not stated
      otherwise. Two test trials were executed using the mean for further statistical analysis.
      Except for maximal isometric leg extension strength and hand grip strength. There, the better
      value of two consecutive trials was used for statistical analysis. In between the trials,
      sufficient recovery periods were provided to reduce fatigue.

      Maximal isometric leg extension strength (ILES) was examined with a cable pull device (Takei
      A5002, Fitness Monitors, Wrexham, England) with an upright body posture. Individual cable
      lengths were chosen to ensure a knee angle of approximately 135°. Participants were asked to
      start "pull[ing] initially with a moderate intensity and slowly increase the intensity to
      maximum exertion while keeping the upper body extended and upright" to prevent injuries. To
      ensure upright posture, participants were instructed to maintain contact between shoulder and
      wall and not lift their scapula while pulling. The test was repeated with at least one minute
      between measurements. The ILES showed excellent test-retest reliability (ICC = .98) for leg
      extension strength.

      To measure handgrip strength a Takei hand dynamometer (Takei A5401, Fitness Monitors,
      Wrexham, England) was used. Participants stood upright with their arm aligned to the body and
      squeeze the device as hard as they could, using the dominant hand. The handle's width was
      adjusted to the participant's hand size. The intermediate phalanges had to be placed on the
      inner handle. The Takei handy dynamometer showed excellent test-retest reliability (ICC =
      .95).

      In addition to isometric strength, power tests were conducted. Supplementary to the standard
      Chair Rise Test (CRT) on stable surface, test trials were recorded while standing on a foam
      pad (AIREX©) as well. Participants had to stand up and sit down five times as quickly as they
      could, without the aid of their arms. Therefore, arms had to be folded across the upper body.
      Time was measured by an ordinary stop watch to the nearest .01 second. After the countdown
      "ready-set-go", testing time was started and stopped when participants were sitting down for
      the fifth time. For the CRT high test-retest reliability has been shown (ICC = .89).

      In addition, a stair climb power test was administered. This test has shown meaningful
      associations with mobility performance and strength measures. Ascent and descent times were
      recorded separately and power was calculated with the following formula: P =((M x D) x g )/t,
      where P = Power (Watt), M = Body mass (kg), D = Vertical distance covered (meters), t = Time
      (seconds) and g = 9.8 (constant of gravity). Participants were instructed to walk quickly but
      safely up and down a 9-step flight of stairs (17 cm step height). Time was started after the
      cue to go and stopped when the second foot reached the top step and/or the floor,
      respectively. Use of the handrail was allowed for safety reasons. Time was measured with an
      ordinary stop watch to the nearest .01 second. Test-retest reliability has shown to be
      excellent (r = .99).

      Balance:

      Dynamic steady-state balance was tested while walking on a 10-m walkway, measuring
      temporal-spatial gait variables (stride length (cm), double support time (%), speed (m/s),
      step width (cm)) using a two-dimensional OptoGait© system (Microgait, Bozano, Italy). In
      addition the coefficient of variation was computed (CV = (SD/mean) x 100). The OptoGait©
      system showed high interclass correlation coefficients (ICC's = .93 - .99) and high
      concurrent validity between the OptoGait© system and a previously validated system.
      Participants were asked to walk for 10 m with their own footwear at a self-selected pace
      three times to calculate test-retest reliability. Because the OptoGait© system is able to
      record automatically, a starting signal was not necessary. A three-minute interval was given
      between individual trials to rest, save the data as well as to prepare for the next trial. At
      the start and the end of the walkway sufficient distance was provided to accelerate and
      decelerate safely. In addition, the first and last step was excluded from analysis to
      eliminate possible acceleration and deceleration bias. Each trial was recorded with 1000 Hz
      using the manufacture provided OptoGait© software running on a laptop computer (Lenovo
      ThinkPad T530).

      Proactive balance was tested using the Functional Reach Test (FRT) and the Timed up and Go
      Test (TUG). The FRT measures the maximal distance participants were able to reach forward
      while standing. For this purpose, participants were instructed lift their dominant arm and to
      reach forward as far as they could without taking a step forward. Maximal reach distance (cm)
      was assessed. The FRT showed excellent test-retest reliability with elderly people (ICC =
      .92). FRT trials were repeated when participants were not able to maintain both feet on the
      ground at a fixed position. In addition to the standard FRT on solid surface, test trials
      were recorded while standing on a foam pad (AIREX©) as well. For the TUG, participants were
      asked to rise from a chair and walk three meters in their normal walking speed around a cone,
      return and sit down. Time for the TUG was recorded with an ordinary stopwatch to the nearest
      .01 second on the command "ready-set-go" and stopped as soon as the participants sat down.
      The TUG showed excellent test-retest reliability (ICC = .99) in older adults.

      To test reactive balance, the Push and Release Test (PRT) was used. The PRT rates the
      postural response to a sudden perturbation. Participants were instructed to push backwards
      against the examiner's hands and to regain their balance after the examiner releases his
      hands. The number of steps required to regain balance was counted and the corresponding score
      was recorded (0 = 1 step, 1 = 2-3 small steps backwards with independent recovery, 2 = ≥4
      steps with independent recovery, 3 = steps with assistance for recovery, 4 = fall or unable
      to stand without assistance). For a detailed description of the PRT see Jacobs and
      colleagues. The PRT showed high test-retest reliability (ICC = .84) with a sensitivity of 89%
      and a specificity of 85%.

      Questionnaires:

      Psychosocial functions were assessed using several questionnaires. Global cognition was
      tested using the MMSE, which is a reliable test for assessing cognitive function showing high
      test-retest reliability (r = .89). The CDT and FAB-D were used to assess executive function.
      Inter-rater reliability of the CDT was shown to be high (IRR = .92) with sensitivity and
      specificity values of .50 and .84, respectively. Falls self-efficacy was measured using the
      German version of the FES-I. This test has shown excellent internal validity (Cronbach's
      alpha = .96) and test-retest reliability (r = .96) to assess the level of fear of falling. To
      assess health-related physical activity, exercise and the amount of energy expenditure, FQoPA
      was conducted. Frey and colleagues showed that FQoPA score correlates with maximum oxygen
      uptake, indicating high validity (r = .42).

      Design of the exercise intervention:

      Participants were stratified into three intervention groups based on equal distribution of
      age and equal gender ratio. The allocation of the training program occurred randomly.
      Intervention group one conducted a 'traditional' machine-based resistance training (M-RT).
      Intervention group two (machine-based instability resistance - M-IRT) followed a similar
      training program with exercise-machines, but with additional unstable devices placed between
      participant and exercise-machine or floor respectively. The third intervention group
      conducted free-weight resistance training on unstable devices (F-IRT) using dumbbells instead
      of exercise-machines. All intervention groups trained for 10 weeks, twice per week on
      non-consecutive days for 60 min. The 10-week intervention period consisted of one week
      introductory phase and three major training blocks lasting three weeks each. Training
      intensity was progressively and individually increased over the 10-week training program by
      modulating load and sets for all groups and level of instability for group M-IRT and F-IRT.
      After week one, four and seven the training load (weight) was increased following 1RM (one
      repetition maximum - maximum amount of force that can be generated within one repetition)
      testing for each exercise. Since the load of 1RM is too heavy for untrained elderly, training
      load was calculated using the prediction equation provided by Epley, showing .03% deviation
      of actual achieved 1RM in squats with a correlation of .97. Instructors made sure that
      repetitions did not exceed 15-20, because 1RM predication accuracy is higher with fewer
      repetitions. Training under unstable conditions, especially with additional weight, implies a
      certain degree of accident risk. Therefore all instability exercises were secured by
      instructors and additional aids like boxes. Training has been supervised by skilled
      instructors. For the first two weeks the participant to instructor ratio was 5:1, afterwards
      10:1.

      Since effectiveness of resistance training to prevent falls has been reported frequently,
      intervention group one (M-RT) acted as an active control group. In a study by Orr and
      colleagues, participants with comparable baseline characteristics showed significant higher
      treatment effects in comparison to a passive control group (p < .001). Since the aim of the
      study was to compare an untested intervention (IRT) and an effective treatment (RT), the
      investigators decided to implement an active instead of a passive control group design.

      Intervention program:

      All three intervention groups conducted a resistance training program consisting of three
      main exercises, a warm-up and cool-down phase. Participants performed 10 min low-intensity
      stepping on a stair-walker as a brief warm-up in the beginning of each training session. The
      core part of the intervention exercises focused on strengthening leg extension muscles.
      Therefore squat-movements were chosen, as recommended by Flanagan and colleagues. M-RT and
      M-IRT groups performed squats on a Smith machine, fixing the barbell at hip level. Pilot
      testing revealed that shoulder and lower back mobility of elderly were too limited for fixing
      the barbell on the shoulders. In addition, the M-IRT group used instability devices (e.g.
      BOSU balls, wobble boards, inflatable discs) placed under the feet. Instability devices were
      used in the F-IRT group as well, but they performed the squat with dumbbells instead of a
      barbell. As a secondary leg extension exercise, leg-press for the M-RT and M-IRT (using
      instability devices put between feet and foot plate) were chosen. The front lunge (with
      dumbbells) was used as a secondary exercise by the F-IRT group. To strengthen the core, the
      bridge exercise was incorporated into the training program. Again, group M-IRT and F-IRT used
      instability devices placed under the shoulder and the feet in addition.

      Statistics:

      An a priori power analysis using G*Power 3.1 with an assumed type I error of .05 and a type
      II error of .10 (90% statistical power) was computed to determine an appropriate sample size
      to achieve statistically significant interaction effects. The calculations were based on a
      study assessing the effects core instability strength training in older adults. The analysis
      revealed the necessity of 54 participants (18 per group) to obtain medium (.24 ≤ f ≤ .39)
      "time x group" interaction effects. Considering the likelihood of dropouts we decided to
      recruit more than 66 participants to compensate a possible dropout rate of 20%.

      Prior to main analysis normal distribution was tested with the Kolmogorov-Smirnov tests for
      each dependent variable. In addition, Levene's test for equality of variance was conducted.
      We tested baseline differences between groups with a one-way ANOVA or a Kruskal-Wallis test
      depending on distribution and homogeneity. In order to test the hypothesis, a 3 (group: M-RT,
      M-IRT & F-IRT) x 2 (time: pre- and post-test) ANOVA, with repeated measures on time was
      calculated. In case of distribution or homogeneity violations non-parametric Friedman and
      Kruskal-Wallis tests were computed to control results of parametrical tests and for
      non-parametrical variables. If differences were detected, non-parametrical results were
      expressed. Because Bonferroni-correction for multiple comparisons has been found too
      conservative, Ryan-Holm-Bonferroni adjusted post-hoc tests were used to analyse significant
      "time x group" interactions or tendencies (.051 ≤ p < .10). Independent t-tests or Mann
      Whitney-U were used to identify differences between groups. Ryan-Holm-Bonferroni corrected
      p-values were reported. In addition, differences in absolute training intensity within the
      last training block were analysed. Thus, the training load of the squat movements, which was
      common to all groups, was used. Differences were computed using a one-way ANOVA. Dependent on
      distribution and homogeneity, Ryan-Holm-Bonferroni adjusted post-hoc tests (independent
      t-test or Mann Whitney-U) were computed to detect differences between groups. Changes for all
      variables within groups were calculated by the formula ∆% = ((Meanpre / Meanpost) - 1) x 100.
      The effect size for ANOVAs' was determined by calculating Cohen's f. Following Cohen,
      f-values ≤ .24 indicate small effects, .25 ≤ f ≤ .39 indicate medium effects and f ≥ .40
      indicate large effects. For post-hoc tests Cohen's d was calculated. Following Cohen,
      d-values ≤ .49 indicate small effects, .50 ≤ d ≤ .79 indicate medium effects and d ≥ .80
      indicate large effects. Significance level was set at α = 5%. All analyses were performed
      using SPSS version 21.0 (SPSS Inc., Chicago, IL, USA).
    

Intervention name(s): Resistance training; Instability resistance training
Intervention type(s): Other; Other
Intervention description(s): traditional resistance training; training under unstable conditions
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Instability resistance training; unstable surface; elderly people