The Feasibility of Whole-Body Vibration Training as an Approach to Improve Health in Autistic Adults

Abstract

Background: Individuals with autism spectrum disorder (ASD) often lead sedentary lives, contributing to cardiovascular disease and muscular atrophy, requiring innovative therapeutic exercise approaches. Whole-body vibration (WBV) exercise training offers a unique option for those with limited motor control. This six-week pilot study aimed to assess the feasibility and effectiveness of WBV training in individuals with ASD. Methods: Six participants (age: 22.17 ± 2.14 years) underwent twice-weekly WBV sessions (10–24 min, 5–25 Hz). Cardiovascular biomarkers, including body composition, leg strength, blood pressure, waist/hip ratio, and body mass index (BMI), were measured. Qualitative outcomes on exercise tolerance, protocol completion, and perceived exertion were collected at each session. Data analyses, including measures of central tendencies and the Wilcoxon Signed Rank Test, evaluated the intervention’s effectiveness. Results: WBV training was safe and well-tolerated in adults with ASD. Despite no statistically significant improvements in cardiovascular and muscular strength indices, participants showed good adherence and tolerance to the protocol. Conclusion: Although WBV training had no significant impact on measured outcomes, it emerged as a feasible and well-tolerated exercise for individuals with ASD. It shows promise for addressing cardiovascular risk factors and reducing sedentary behaviors, suggesting the need for longer interventions to fully uncover its therapeutic potential.

1. Introduction

Autism spectrum disorders (ASD) are characterized as complex developmental disorders, with individuals exhibiting deficits in communication, behavior regulation, and social engagement. New cases exceed 2% of the population each year [1], and the Centers for Disease Control and Prevention (CDC) report that 1 in 36 are currently diagnosed with ASD, a staggering increase from the 1 in 150 data published in 2000 [1]. Cardiovascular disease is the primary cause of death in the United States with healthcare expenditures totaling 363 billion USD annually [2]. Individuals with ASD are at particular risk for cardiovascular disease (CVD), and research highlights that CVD is the leading cause of mortality in this population [3,4]. Additionally, it has been reported that sedentary behavior, defined as both low leisure time and general physical activity levels (<1–1.5 METs (metabolic equivalents), is linked to hypertension, diabetes, and obesity, each of which are contributing risk factors or morbidities associated with cardiovascular disease [5,6].

An estimated 5,437,988 (2.21%) adults in the United States have ASD [1], which illustrates a significant need for preventive health care strategies as this population ages. Individuals with ASD typically have higher overall body mass index (BMI) [7,8,9], rates of hypertension and diabetes [7], and arterial stiffness [9,10] than their neurotypical peers, implying a greater susceptibility to CVD. Furthermore, sedentary behavior is exacerbated within this population due to several barriers, including access to, and opportunities for, exercise, resulting from behaviors associated with ASD such as perseveration, hypersensitivity, aggression, and impaired motor skills [11]. More recently, increased stress and anxiety associated with the COVID 19 [12] pandemic may have exacerbated leisure time inactivity in certain populations, thus increasing the risk of premature death due to cardiovascular diseases such as atherosclerosis. Physical activity in the general population improves physical and mental health, yet research in the ASD population is lacking, but is necessary since autistic individuals are often not similarly engaged in exercise that is fun and approachable [13]. Indeed, adherence to any physical activity program will suffer if the participant finds no enjoyment in the experience. Additionally, evidence-based interventions (i.e., Step UP program or FitSkills) that require coaches, mentors, community partnerships, and wearable technology may also limit participation and serve as additional barriers to regular physical activity [14,15]. Therefore, implementing unique strategies to overcome barriers to exercise and improve physical health, such as cardiovascular profile, in the ASD population, apart from traditional dietary/exercise approaches, are essential.

Whole-body vibration (WBV) is a novel exercise therapy that has shown promise in the literature as an alternative approach to structured exercise by imposing physiological stress and promoting beneficial health-related adaptations in various populations [16]. WBV technology is characterized by multidimensional oscillations emitted from a platform which are transmitted from the feet to the rest of the body [17]. Whole-body vibration is a therapeutic intervention that exposes the body to mechanical vibrations while the subject sits, stands, or lies on a vibrating platform. Physical improvements may be observed by standing on the platform or by simultaneously performing various exercises such as squats, lunges, planks, and tricep dips. The vibration machine transmits energy in the form of increased gravitational force to the body, which stimulates muscles to contract and relax multiple times each second. This approach was first used to treat gait disorders in neurological patients, and is currently widely implemented in rehabilitation settings to improve lower back pain, sarcopenia, muscle function, muscle soreness, joint stability, and reduce falling risk [18]. One mechanism of action for WBV is the tonic vibration reflex (TVR) [18], which enhances motor unit recruitment and the gradual development of muscle activity, as well as increases intramuscular temperature and peripheral blood flow. The vibrations of the WBV machine are set to a precise frequency (Hz) and amplitude (mm) in order to regulate the intensity of stimulation. For instance, if the frequency is set to 30 Hz, the targeted muscle(s) receives 30 cycles of vibration per second, which subsequently stimulates the muscle(s) to contract and relax 30 times each second. The higher the frequency, the greater the stimulus and the more work performed by the muscle. Improved muscular capacity can be achieved by performing as little as two to three training sessions per week, each lasting between 10 and 15 min duration [19]. After a period of initial exposure to WBV training, participants generally become well-accustomed to increasing exercise intensity (e.g., manipulation of frequency, amplitude, or both), with few if any notable difficulties [19,20,21].

The WBV device is particularly helpful in individuals who are immobilized due to chronic health issues or have prolonged injuries, as typically seen in special needs, aging [22], overweight, and obese populations, as it is considered to be passive training, involving minimal risk of injury [23]. Prior research using WBV interventions have shown improvements in cardiovascular health [17,24], arthritis [25], flexibility [26], muscle soreness/stiffness [26], muscle strength/power [27], motor function and balance [28], and bone density [29] within mixed populations. However, to date, there is no published literature on the feasibility of WBV exercise training on autistic individuals or cardiovascular disease risk factors in sedentary and/or overweight individuals with ASD. In particular, WBV exercise training may be beneficial in immobile individuals with chronic conditions, such as ASD, as a viable surrogate to traditional exercise programs that often assume participants have no physical and/or other limitations for prolonged participation [8].

The established literature on the positive effects of WBV training in various populations has focused on older adults [18,22,30], post-menopausal women [31,32], those with neurological conditions [33,34,35], and athletes [36]. However, the literature on WBV in unique populations similar to ASD with deficits in motor control and physical fitness (e.g., Down syndrome and cerebral palsy) is limited but continues to emerge. Whole body vibration training has been shown to be a partially effective approach to improve the strength and body composition of persons with Down syndrome (DS) [21,37,38] and for muscle strength, coordination, and spasticity in patients with cerebral palsy [23,39]. Studies on these populations are limited and require further larger scale investigations. Similar to individuals with ASD, adults with DS are three times more likely to be overweight or obese [40] and have overall poor physical fitness and body composition. Thus, increasing lean body mass in the ASD and DS populations may lead to greater independence and an improved quality of life [37]. Additionally, WBV training has elicited improvements in muscle strength, bone mineral density, body composition, and balance in adolescents with DS [21]. Cerebral Palsy (CP), a neurological disorder that affects muscle coordination, body movement, posture, and thus overall mobility, has also found benefit following WBV training where improvements in walking and mobility have been observed, specifically related to gait speed, stride length, cycle time, and ankle angle [39]. A review article by Ruhde and Hulla [23] outlined the benefits of WBV on CP and found several investigations that identified improvements in physical performance characteristics, such as balance/gait, bone density/mass, spasticity, and strength/power. In summary, these findings illustrate that WBV training has the potential to be a viable solution for improving health and physical impairments related to CVD and motor deficiencies in individuals living with special needs.

The purpose of this study was to assess the feasibility of a six-week WBV training program on individuals with autism. While WBV training is an effective exercise modality among several populations, there is at present no documented research on WBV training and its effect on cardiovascular and muscular strength indices in the ASD population. Thus, this research study investigated the feasibility of WBV training, regarding these primary qualitative objectives: completion of the protocol, adverse effects of WBV on this population, ease of instruction and implementation of the intervention, and tolerance and progression of an exercise protocol, as well as secondary objectives that included outcomes of leg strength, BMI, waist/hip ratio, body composition, and blood pressure in individuals with ASD.

2. Methods

2.1. Design

This research employed a participant fidelity physical activity intervention feasibility study design to determine if WBV was an appropriate and well-tolerated exercise intervention for the ASD population. Participant fidelity denotes the extent to which participants successfully adhere to the intervention protocol or prescribed physical exercises [41]. This type of design can help to advise further, larger, and longer research by evaluating the initial aspects of the intervention recruitment, delivery of the protocol, and participant adherence as measurable outcomes [41]. Feasibility studies are important to assess the research and intervention processes in the preliminary examination of a study’s objectives and guiding questions to help direct additional research [42]. Additionally, this study incorporated a pre-/post-test design on various health biomarkers indicative of cardiovascular health, including body composition (body fat percentage; % BF), leg strength, blood pressure (BP), waist/hip ratio (WHR), and body mass index (BMI) to determine participant tolerance of assessments and the short-term impact of WBV training.

2.2. Participants

Over a five-week period, researchers recruited a convenience sample of ASD adults (n = 6; age, 22.17 ± 2.14 years) through various social media sites, a local university, community housing cooperatives, a local special needs hockey team, and word of mouth. Inclusion criteria included individuals ≥18 years old diagnosed with ASD who were able to communicate verbally or with a communication device. Participants were also required to understand simple commands and be physically capable of performing exercises (ex: squats, calf raises) and have no health conditions contraindicated to WBV. Additionally, it was required that all participants have a caregiver attend each session. This was important for comfortability, facilitation of communication, and overall safety of the participants. Conversely, exclusion criteria included individuals with acute thrombosis, acute hernia, epilepsy, gallbladder or kidney stones, recent wounds from surgery, recent fractures, acute pain or inflammation, and those who were pregnant. Participants reported to a laboratory-controlled environment, and undertook two WBV sessions per week with a minimum of one day separating each session. Participants were provided with a monetary honorarium for their participation in this study.

2.3. Procedures

Following IRB approval, all participants, upon review of the informed consent by the investigators and/or guardians, provided consent and signed their own names. Researchers emailed participants (and parents/caregivers) the intervention calendar to schedule twice-weekly WBV training sessions. During the initial session baseline, (pre-) measurements were taken for WHR, % BF, height/weight (BMI), leg strength (wall-sit), and BP. Blood pressure was assessed prior to every session after participants had entered the lab and were seated calmly for approximately 5 min. After a brief demonstration, the wall-sit required minimal practice for participants to successfully complete the procedure. Midway through each exercise, session participants were asked their rating of perceived exertion (RPE) level. A unique and non-traditional approach to RPE was utilized where participants pointed to a number, color, or verbally indicated their RPE on a scale (see Figure 1). If the RPE was ≥8, participants were asked if they desired to have the intensity reduced, stop the exercise session, or continue with the exercise. Post-intervention outcomes were obtained in all participants, after a period of rest and following the final WBV session, for body mass, blood pressure, leg strength, waist/hip ratio, and body composition.

2.4. Measures

In addition to the pre-assessment (baseline) and demographic information, researchers evaluated participants for each of the following qualitative feasibility outcomes through a series of questions: (1) Did the participant complete the exercise trials? (2) Did the participant feel comfortable and tolerate the WBV machine? (3) Was the intensity of the machine reduced at any time? Why or why not? (4) Was the participant well-regulated and safe (able to move their body without distractions or loss of balance), and (5) Did the participants’ parent(s) or caregiver(s) have any questions or concerns? Participant success for each of the questions was determined through several hypotheses stated below. Weight and height were measured without shoes using a standard stadiometer, and subsequently body mass index (BMI) was calculated via kg/ht (m)². Systolic and diastolic blood pressure were measured using an automated blood pressure device (Omron Healthcare, Inc, Osaka, Japan) at the beginning of every WBV training session, as noted. The waist/hip ratio was calculated using the average of two circumference cloth tape measurements (inches) of the waist (smallest portion of torso) divided by the average hip measurement (widest part of hip/buttocks). Participants were standing for the waist/hip assessment, and measurements were taken over thin clothing to avoid sensory discomfort. Leg strength was measured with an endurance wall-sit. Participants stood with their feet facing outward in front of a blank wall and slid their back down until their hips were in-line with their knees. Their hands were made to hang by their side, and participants held the position for as long as they could and were timed using a stopwatch [44]. Poor body control affected their ability to hold the wall-sit, and, along with asking them to stop, were indications for terminating the test. Body composition (% BF) was evaluated using a hand-held non-invasive bioelectrical impedance analyzer (BIA) device (Omron Healthcare, Inc). To maintain reliability, all pre- and post-intervention assessments were taken by the same trained researcher. Using the CONSORT statement for feasibility studies as a guide [41,45,46] predetermined criteria for feasibility success in the present study were hypothesized as follows: (1) there would be minor changes in health outcomes from pre- to post-intervention as measured by the WSRT; (2) a total of 10 participants meeting the inclusion criteria would be recruited for the study; (3) each participant would complete at least 10 out of 12 total WBV training sessions, and there will be an overall WBV training protocol rate of progression of 90%; (4) participants will complete 95% of all health assessments; (5) consent from all participants meeting the inclusion criteria would be obtained; and (6) participants would have minimal to no adverse effects from the WBV machine that would limit or terminate participation.

2.5. WBV Intervention

The Hypervibe™ WBV machine (model G14) was used for the six-week intervention training sessions in a temperature-controlled laboratory environment. The machine utilizes manual and pre-programmed exercise sessions that vary the type of exercises, total exercise time, and hertz (Hz) level. The exercise protocol involved having participants complete the first week of WBV training by standing on the activated WBV machine and then progressing in subsequent weeks by performing various exercises on the vibration platform. All participants during week one were initially assimilated to the WBV device by using the manual setting controlled by researchers for 10 min at 5 Hz in session one and 5–7 Hz for 10 min in session two. Participants stood on the machine in a normal stance about shoulder width apart, with socks on, for the entire 10 min, and used the handlebars for support. The manual program setting facilitated an introduction to the WBV machine and for researchers to monitor for any adverse events, since WBV represented a novel mode of exercise stimulus for all study participants.

Table 1. WBV intervention training schedule for ASD participants.

	Week 1	Week 2	Week 3	Week 4	Week 5	Week 6	Make up Week e
Hertz (Hz)	S1: 5–7 S2: 6–7	S1: 8–15 S2: 8–15	S1: 6–18 S2: 6–18	S1: 6–24 c S2: 6–24 c	S1: 12–24 S2: 12–24	S1: 12–25 d S2: 12–25 d	S1: 12–25
Number of exercises	S1: 1 S2: 1	S1: 12 S2: 12	S1: 15 S2: 15	S1: 15 S2: 15	S1: 14–15 S2: 14–15	S1: 10–14 d S2: 10–14 d	S1: 14
Total time (minutes)	S1: 10 S2: 10	S1: 21 S2: 21	S1: 23 S2: 23	S1: 23–26 c S2: 23–26 c	S1: 23–26 S2. 23–26	S1: 19–24 S2: 19–24	S1:24
Rating of Perceived exertion (RPE: 1–10)	S1: 1–3.5 S2: 0–8 a	S1: 1–6 b S2: 1–7	S1: 2–6 S2: 1–9	S1: 2–7 S2: 2–7	S1: 2–7 S2: 2–7	S1: 1–7 S2: 1–8 f	S1: 7

Notes: All values are ranges (aggregated) for all participants; S1 = first session of the week; S2 = second session of the week. ^a One participant was moved to 5 Hz after a high RPE. ^b One participant did not finish S1 and did not report RPE. ^c One participant advanced, while five others stayed at the same level. ^d One participant went down a level due to issues performing exercises. ^e One participant extended a week for make-up sessions. ^f Participant remained at the same intensity despite an RPE ≥ 8.

outlines the intensity, duration, and number of exercises completed each week by the participants. The intensity (Hz), number of exercises, and total exercise time were increased each week. During week two, participants engaged in a pre-programmed WBV exercise session called the “active aging strong and stable” category designed by Hybervibe™. This category was selected due to its simplicity of WBV exercises (e.g., standing at various widths, alternating knee lifts (see Figure 2), single leg standing, step ups, step up with knee, and standing lumbar massage), shorter duration, and slightly higher Hz levels (8–15 Hz). Week three had participants moving to the “active aging fitness beginner” category (6–18 Hz), with exercises on the WBV consisting of those from the previous session and new routines that included mini squats, modified push-ups (with hands on the machine and knees on the ground), bicep curls, calf raise, standing hamstring curl, planks (with hands on the machine and feet on outstretched behind them; see Figure 3), hip abductions (see Figure 4), and hamstring stretches. Weeks four and five were termed “active aging fitness intermediate” (12–24 Hz; see Figure 5), with new additional exercises consisting of deep squats, triceps dips, pelvic tilts, and hip bridges (laying on a mat with feet on the machine). Finally, week six had participants perform the “active aging fitness advanced” (12–25 Hz) program consisting of exercises from week five with a lateral side alternating step up. Two participants continued with the “active fitness intermediate” for an additional week due to the complexity of the exercises (e.g., self-perceived difficulty to perform) and complaints of “minor” muscle soreness. During week 5, one participant moved to a “bone building” program (15–24 Hz) involving fewer exercises due to the participant lacking the necessary motor control skills needed to perform the more advanced exercises. The “bone building” program was selected, since it utilized similar Hz values to the other participant’s training programs.

Participants were asked to indicate their rating of perceived exertion (RPE) using a novel color and facial expression 0–10 scale at the midpoint of each WBV training session. This particular RPE scale (see Figure 1) was used to ensure that if a participant was unable to understand or relate to a number equivalent value for the traditional Borg RPE Scale, they could then use surrogate indices including pictures and/or colors to identify their level of perceived exertion. For example, one end of the scale is represented by the color red and a frown face (0 numerical value equivalent), whereas the other end of the scale is indicated by green and a happy face (10 numerical value equivalent). If, during WBV training, a participant selected an RPE rating that was at a level of eight or higher, they were asked if they desired to have the intensity of the WBV machine reduced. To promote participant safety, a CPR/First Aid certified researcher was present during all training sessions, and an automated external defibrillator (AED) was available at all times. Researchers were positioned adjacent to each participant during WBV training to provide tactile cues (e.g., touching the knee or leg) when necessary to ensure that proper form for each exercise was followed. Additionally, a parent(s) and/or caregiver(s) was present during all WBV sessions to assist researchers in communicating with participants (e.g., one participant utilized an augmented alternative communication device) and that individual’s sensory and motor needs were being addressed. Researchers were prepared for possible adverse events through constant monitoring of participants and by documenting feedback during and after each exercise session, respectively. If adverse or unusual sensitivities were reported, these were documented on the participant’s data sheet and were monitored during subsequent WBV training sessions.

2.6. Statistical Analyses

Qualitative data analyses (e.g., feasibility of WBV training in the ASD population) consisted in the rate of progression and tolerance to WBV training, as described above, and any complications in participants that arose during the training sessions. As part of the feasibility design of this study, we evaluated recruitment rate, consent rate, and study retention rate, with the indicators of success specified above [41]. Additionally, further qualitative/quantitative analyses were designed to assess the feasibility of a short-term exercise (WBV training) intervention on health outcomes (tolerance of assessments and pre-/post-intervention alterations) to further assist in developing appropriate WBV interventions (intensity and duration). As such, descriptive statistics for pre- to post-intervention data for all outcomes are presented as means and standard deviations (±SD; see

Table 2. Pre-/post-mean (SD) and -median values for cardiovascular and muscular strength outcomes.

	Baseline (Pre)	Post-Intervention	Pre-Percentiles (50th) Median	Post-Percentiles (50th) Median
Body mass (kg)	73.41 ± (15.71)	73.13 ± (13.93)	71.37	72.96
BMI (kg/m2)	25.16 ± (4.30)	25.07 ± (3.70)	21.59	21.93
Body Composition (% BF)	26.46 ± (7.97)	27.24 ± (8.32)	29.80	30.00
WHR a	0.848 ± (0.080)	0.826 ± (0.086)	0.846	0.795
Leg Strength (s) b	20.55 ± (15.06)	28.46 ± (12.16)	13.35	29.89
Systolic BP (mmHg)	119.83 ± (13.72)	123.33 ± (8.52)	117.0	118.5
Diastolic BP (mmHg)	76.83 ± (8.86)	76.67 ± (6.74)	76.0	78.0

Notes: All values are expressed as Means ± (SD). ^a WHR = ratio of waist to hip measurements in inches. ^b Leg strength = wall sit duration in second.

). In addition, median differences between pre- and post-WBV training assessments (BMI, WHR, % BF, leg strength, systolic/diastolic BP (mmHg)) were analyzed by utilizing a Wilcoxon Signed Rank Test (WSRT). The WSRT is a non-parametric participant ranking statistical tool for hypothesis testing used for smaller samples when there are a range of data without normal distribution [47]. The WSRT may be used as an alternative to the t-test when determining if a population’s matched samples are different or if the median is nonzero. Analyses for the cardiovascular biomarkers pre- to post-intervention were performed using the Statistical Package for Social Sciences (SPSS) version 29 software. Statistical significance between pre- and post-intervention measures was determined at p ≤ 0.05.

3. Results

Five participants completed the entire six-week intervention (twelve sessions), and one participant completed ten sessions and opted out of the final week due to parental concern regarding obsessive compulsive behaviors. This resulted in a high retention rate, which met our goal of participation in at least ten sessions (100%). Nine participants first responded to requests to participate, and of those, six met the inclusion criteria. The research team planned for at least ten participants; however, of the nine interested, only six followed through with consent and in scheduling sessions, resulting in a recruitment rate of 66%, four fewer participants than originally intended. Participants demographics included: age: 22.17 ± 2.14 years with equal distribution for sex (three = males, three = females). One participant was non-speaking and communicated with a communication board, while the remaining five participants were verbal and mostly independent. Four of the six participants met the criteria for engaging in recommended regular levels of physical activity per week (self-reported, or as reviewed with parent/caregiver, participating in ≥150 min of moderate activity/week) while two participants were currently sedentary ([48], p. 7). Table 1, as noted, illustrates the week-by-week WBV training intervention schedule for each participant, which was individualized based on participant feedback and observations made by researchers. One participant struggled with performing the exercises, and thus was moved to a more basic program with similar Hz levels to mirror, as best as possible, the other participants. Figure 6 below outlines the main outcomes for stated hypotheses regarding the feasibility of WBV training and health-related assessments in an ASD population. The WSRT indicated no statistically significant alterations in any of the measured cardiovascular or strength variables from pre- to post-intervention (see Table 2).

Qualitative Feedback from Study Participants

Communication proved to be limited among participants during WBV training sessions, thereby preventing any formal analysis or generation of common themes, and thus researchers relied primarily on observational data. Despite minimal negative feedback from participants, one individual in the current study complained of “itchy legs” during each training session, likely from the repeated up/down movements of the WBV platform, but it was not enough to deter participation or completion of the sessions. This particular participant (who was sedentary prior to the intervention) also commented that the exercises “hurt” but felt “good”. As mentioned, two participants felt confused by the RPE scale and did not find it to be a true representation of physical exertion, and alternative means of establishing perceived exertion in the ASD population should be explored. Only one exercise proved challenging for all participants to complete, the pelvic tilt, which had participants standing on the moving WBV platform while contracting their abdominal muscles and tilting their hips forward. They were advised and/or coached to continue to attempt the exercise or, as needed, participate in an alternate exercise, such as the lumbar massage. Other feedback from one caregiver indicated that their dependent “enjoyed” the laboratory environment, and another parent mentioned that they were considering the purchase of an WBV machine for their home due to “ease of use”. Also, many times, parents/caregivers commented that the supervised training sessions provided positive social opportunities and interactions for their dependents.

4. Discussion

4.1. Feasibility of WBV Training in an ASD Population

The researchers in the present study successfully implemented a six-week WBV training intervention in ASD individuals to include pre- to post-intervention cardiovascular disease biomarkers and muscular strength measurements. Despite allowing for a five-week recruitment period, initial recruitment of participants proved challenging, with an overall rate of 66% (six out of nine individuals) committing to study participation. The mandatory attendance of caregivers at all sessions may have served as a deterrent, impeding broader participation. In those ultimately participating, WBV training demonstrated to be a safe and well-tolerated intervention, causing no serious adverse side effects (0% adverse reactions) similar to other WBV interventions in special populations [19,20,21]. One participant failed to complete the entire 6-week training protocol, as noted; however, this still resulted in a 100% retention rate based on our hypothesis. Furthermore, all of the participants (100%) completed all of the exercises on the WBV machine with minimal effects that limited or ceased participation. However, one participant spent the last week at a lower intensity program due to motor-skill struggles when performing exercises which lowered the protocol rate of progression to 97% (35 actual sessions/36 potential sessions) This population was willing and excited to participate in research, and welcomed the social engagement of the weekly sessions. Participants needed minimal familiarization to learn the assessments, and cooperated fully while on the WBV machine. Scheduled rest periods of 1 min between exercises allowed the participants to recover as needed, although only two participants utilized this option. Sensory differences are very common among individuals with ASD, and can manifest as tactile, visual, auditory, and movement sensitivity, as well as sensation-seeking behaviors [49]. Such differences were evident throughout the WBV intervention; however, they varied among participants. For example, one participant needed a “sensory break” to move around and draw pictures on a white board, while another participant felt “itchy” from the muscle activation/vibration and needed time (<1 min) before starting a new exercise. One participant brought their beloved stuffed penguin to train on the WBV machine and another recited various episodes of Garfield to maintain comfort during the sessions. All of these sensory phenotypes were welcomed, and helped participants partake in and/or complete each exercise training session. Interestingly, a single article that sought to evaluate the effects of WBV on the frequency of stereotypical behavior in young children with ASD found that WBV training did not decrease the rates of stereotypical behaviors, but that all the participants enjoyed the WBV sessions [50], results that were similarly observed in the current research investigation. However, the Bressel et al. [50] study, while the first of its kind to report on WBV in autistic individuals, was limited in exposure to the WBV machine and did not track stereotypical behaviors over a training intervention protocol.

An additional benefit of certain WBV machines, unlike other more typical exercise modalities, aside from preprogrammed exercise protocols and rest periods, was the ability to demonstrate an upcoming exercise as displayed on the video screen (see Figure 5). Such visual representation of the exercise directed the attention of participants to the correct exercise form for which they were about to undertake. Furthermore, this also facilitated independence among participants, who continued the exercises at their own self-directed pace without rest. The participants were subsequently able to complete the following exercises at various Hz levels (5–25): normal, wide, and wider stance on the WBV platform (see markings along bottom edge of platform in Figure 3), a stance with head turns, tricep dips, squats (mini and deep), lumbar massages, modified push-ups, bicep curls, hip bridges, planks (see Figure 2), alternating abductions (see Figure 3), hamstring stretches, calf raises, side steps left/right, and alternating step ups with knee lifts (see Figure 4). All participants successfully completed each session, except one participant, whose obsessive compulsive behaviors (OCD) became too disruptive, resulting in the need to end the last session after ten minutes. The participants’ parent felt that the behavior was not related to the intervention, but was rather a result of their existing OCD behaviors associated with their autism. Otherwise, the participants were very compliant, and all but one could tolerate increasing the intensity (Hz), duration (minutes), and number of exercises over the 6-week intervention period. This was further evidenced by a consistent RPE observed throughout the duration of the training sessions and from one training session to the next, despite an increase in overall exercise volume.

4.2. Cardiovascular Biomarker and Muscular Strength Outcomes

Five of the six participants successfully completed the pre-assessments, despite certain sensory complaints like the ‘tearing’ sound of Velcro and the tightness of the blood pressure cuff. As previously noted, one participant was unable to hold the handheld BIA device for an appropriate reading. Additionally, since one participant missed the last two sessions, they also missed two blood pressure readings. Therefore, the total participation in pre- and post-assessment measurements was 97%, which exceeded our hypothesized criteria of 95% (122 actual out of a maximum of 126). Other devices for measuring body composition, such as a BIA leg-to-leg scale, should be considered if handheld devices prove challenging in this population. Participants needed minimal prompting and instruction and were very cooperative, which should prove helpful for future research.

Despite there being no statistically significant change in CV disease biomarkers and muscular strength in the current investigation, a review article by Matute-Llorente et al. [19] on the effects of WBV on physical fitness in children and adolescents with disabilities explained that WBV can elicit beneficial improvements in bone mineral density, muscle strength/power, gait speed, balance, lean body mass, and body fat. However, prospective studies in this article ranged from 8 to 52 weeks, and it was suggested that interventions three times a week ranging from 10 to 20 min at higher frequencies (15–35 Hz) may be the most appropriate protocol to elicit improvements in body composition and strength [19,21]. Saquetto et al. reviewed WBV training on children and adolescents with DS, and indicated that significant increases in strength were observed [21]. However, as above, these studies incorporated longer intervention periods of 12–24 weeks at higher frequencies (25–30 Hz) utilized over three sessions per week. Furthermore, the studies included in this review focused on simple standing and squatting exercises, and did not investigate the feasibility of a variety of full-body exercises as used in the current research investigation. Whether WBV training at higher overall volumes (e.g., duration, intensity, frequency) in an ASD population proves feasible in modifying CV disease biomarkers remains to be determined.

An analysis of individual data of ASD participants in the present study indicated that baseline values for CV disease biomarkers, including WHR, BMI, and BP (two participants) and % BF (three participants), would be considered unhealthy for the general population ([48], p. 7). Thus, improvement in any of these variables, would reduce health risks related to cardiovascular disease and obesity. In fact, the ACSM (American College of Sports Medicine) ([48], p. 65) indicates that a WHR in adults above 0.95 for males and 0.86 for females increases obesity-related health risk resulting from central obesity, and may for this reason be a superior measure to BMI. Despite having similar BMIs to the participants in the current research, work by Gonzalez-Aguero et al. [37] showed improvements in body composition in adolescents with DS after a 20 week, three times per week intervention. Collectively, this confirms the need for longer and more frequent exercise training sessions to elicit changes in body composition. Whereas most of the literature has focused on adolescents or children with special needs, adults with special needs remains an underrepresented population within the literature, and future studies are justified to elucidate the implications of WBV training in this population. Furthermore, WHR, BMI, and BP were not routinely measured in the aforementioned investigations, as bone mineral density, gait, and balance were prioritized in younger populations where mobility, strength, and spasticity are critical outcomes, as opposed to cardiovascular disease risk outcomes, which may be more relevant in an adult and/or aging population.

4.3. Strengths and Limitations

Apart from the pioneering yet now dated work by Bressel et al. [50] that focused on the impact of five-minute WBV sessions on stereotypical behaviors in children with ASD, this is the first study of its kind to investigate prolonged WBV training as a non-traditional exercise modality in the adult ASD population. Strengths of this study include a high compliance rate (83%) and an equal distribution of male (n = 3) and female (n = 3) participants who demonstrated minimal acute adverse side effects or indicated few complaints during the entire six-week WBV intervention. Visual aids of each exercise, as well as familiarization via practice and demonstration on the WBV machine, were seemingly important advantages in maintaining compliance and focus in this population. Limitations include a small sample size, despite offering financial incentive; however, of those who participated, parents/caregivers and participants alike were intrinsically motivated to be involved in the study. Outside of the goal to obtain ten participants for the study, we were able to meet all of the other proposed success criteria for feasibility of WBV training for this population. Due to this, WBV should be considered to be an emerging exercise modality for the ASD population. One contradiction to WBV training is epilepsy, where reportedly 20% of individuals with autism are also diagnosed with concurrent epilepsy [51], which in turn may have limited participation (as an exclusion criteria). The presence of a caregiver(s), guardian(s), and/or a parent(s) was required for all but one participant during all WBV training sessions, which may have influenced recruitment. Due to sensory complications oftentimes associated with autism, waist/hip measurements were taken over light clothing, which may have impacted results. Also, one participant could not hold the handheld BIA device correctly, and this data were not included in statistical analysis. Two participants mentioned that, despite efforts to simplify the RPE scale, it was confusing, and thus their perceptions may not have been the best representation of true exertion. Lastly, as the current study was of a rather acute feasibility design, there was a lack of more complicated research methodology, such as randomization, cross-over design, or control group.

4.4. Implications for Future Research

Since recruitment proved to be challenging, future research may consider utilizing portable WBV machines and bringing the device to living facilities or recreational centers to enhance supervision, social interaction, and provide longer duration interventions. The preliminary findings of this investigation indicate an encouraging role for WBV exercise in the autistic population, since WBV training and associated assessments were well tolerated by the participants. More vigorous WBV interventions as participants progress in their tolerance (e.g., higher Hz or additional exercises) are warranted over greater durations (e.g., 9–12 weeks), which may help sedentary individuals achieve the recommended levels of weekly physical activity and possibly elicit improvements in both cardiovascular health outcomes and muscular strength. Other cardiovascular disease biomarker outcomes, which are often negatively impacted by a sedentary lifestyle, such as metabolic panels (e.g., lipids, cholesterol, glucose, etc.), may also show improvements following WBV training, although blood draws or finger pricks may pose a problem in this population and should be an important consideration during research design.

5. Conclusions

Whole body vibration training appears to be a feasible and well-tolerated alternative to traditional exercise programming in individuals with ASD who exhibit few comorbidities, particularly those with epilepsy. The feasibility of WBV training in the adult ASD population appears to be enhanced with frequent rest periods or stimuli breaks, as well as demonstrations and/or visual aids of specific exercises that were to be performed by participants on the WBV platform. Future investigations should consider longer duration interventions to elicit improvements in health indices, including cardiovascular disease markers and measures of muscular strength, as these assessments were well tolerated by participants in the present study.