October 05, 2020


The XOTrainer™ wearable arm exerciser is a resistance training exoskeleton that strengthens arm muscles, tones your arms, and helps you lose unwanted arm fat — all without traditional exercising, without a long-term commitment to a fitness center, and without expensive equipment. Order The Works Kit today and try it for 90 days Risk Free!  XOTrainer™

OU study completed!  Shows definite gains! 

Here is the final study results done by the School of Exercise Science, University of Oklahoma:

Executive Summary and Final Report


  • Testing in the current investigation represented a repeated measures design where participants were compared prior to and 8 weeks following the use of the XOTrainer. The device was worn on the dominant arm, and was then compared to itself and the non-dominant arm was used as a control.  The variables of interest were as follows:  relaxed and flexed arm circumference, biceps and triceps thickness (measured via Ultrasound in duplicate), waist circumference, hip circumference, body composition (measured via bioelectrical impedance), along with isokinetic testing for changes in peak force, average force, average power, and total work across 3 contractions.  Isokinetic testing was chosen to decrease error variability due to range of motion utilized and movement technique.  Participants were asked to wear the device for 4 hours per day but were allowed to wear it any additional amount of time they saw fit.  Participants were asked to keep physical activity similar over the 8-week period, as well as, their nutritional and supplement/vitamin/mineral intake.  Participants were all pre-screened for any risk factors that may preclude them from participating fully in the investigation. 
  • 18 participants completed the study.
  • Key Findings of the Study


  • Isokinetic muscular testing
    • Peak Torque: Following 8 weeks of use with the XOTrainer, there were increases in low-speed/high-force, as well as, high-speed/low-force peak extension torque for both arms, but no changes in flexion peak torque in either arm.  Additionally, the increase in both arms was similar.
      • This finding demonstrates the ability of the trainer to promote changes to both the ipsilateral (same) arm as well as the contralateral (opposite) arm.
      • It appears the triceps are stimulated by the XOTrainer to a greater degree compared to the biceps. This could be due, in part, to a biasing of “pulling” movements used in activities of daily living, thus providing a greater opportunity for positive changes in the “pushing” movements related to the triceps musculature.
    • Average Work: Following 8 weeks of use with the XOTrainer there were no improvements in low speed/high force work output in either flexion (biceps) or extension (triceps) at the elbow, however there was a trend towards improvement during high speed/low force extension work for both arms, but not with high speed/low force flexion.
    • Average Power: Following 8 weeks of use with the XOTrainer there were improvements in low speed/high force and high speed/low force power in both arms during the extension phase of movement with the arm wearing the device demonstrating a significantly larger increase.  However, neither arm saw an increase during the flexion phase of the range of motion. 
      • This finding, taken with those previously mentioned, further demonstrates both the cross-education effect mentioned earlier (training one side of the body results in improvement in both sides), as well as, a biasing in both muscular anatomy and muscular performance for the extension phase of elbow movement with the XOTrainer. This may be a valuable finding demonstrating the XOTrainer’s ability to improve a health/fitness-related parameter that may increase the ability to perform activities of daily living.
    • Muscle hypertrophy changes to biceps/triceps thickness
      • Biceps: Following 8 weeks of use with the XOTrainer, both arms experienced an increase in biceps thickness, with the dominant arm (the arm the device was worn on) showing a larger increase in size. 
      • Triceps: Following 8 weeks of use with the XOTrainer, both arms experienced an increase in triceps thickness, with the dominant arm (the arm the device was worn on) and non-dominant arm showing similar increases in size. 
    • Flexed and relaxed arm circumference
      • There were no statistical changes to either relaxed or flexed arm circumference before and after use of the XOTrainer
    • Body composition
      • Body composition (proportion of lean mass, such as bone and skeletal muscle vs. fat mass) remained unchanged from before and after use of the XOTrainer
    • Waist/Hip circumference
      • Waist circumference remained unchanged from before and after use of the XOTrainer
      • Hip circumference remained unchanged from before and after use of the XOTrainer
    • Blood pressure
      • Blood pressure remained unchanged from before and after use of the XOTrainer


  • Isokinetic muscular testing
    • 61% of participants increased peak torque during extension in the dominant arm at 600/s while 72% increased at 1800/s.
    • 78% of participants increased peak torque during extension in the dominant arm at 600/s and 67% participants increased at1800/s.
    • 56% of participants increased peak torque during flexion in the dominant arm at 600/s and 1800/s, respectively while 67% and 61% increased the same measures in the non-dominant arm
    • 56% and 67% of participants increased total work performed during flexion at 600/s and 1800/s, respectively, in the dominant arm; 67% of participants and 50% of participants improved these same measures in the non-dominant arm.
    • Average power during extension at 600/s and 1800/s was increased by 83% at both speeds in the dominant arm and at 72% and 78% in the non-dominant arm for the same variables. The changes in average power for flexion were only experienced by a few individuals.
  • Muscle hypertrophy changes to biceps/triceps thickness
    • Biceps: Following 8 weeks of use with the XOTrainer, 78% of individuals experienced an increase in biceps thickness, in the dominant arm (the arm the device was worn on) while 56% experienced an improvement in the non-dominant arm (no device) 
    • Triceps: Following 8 weeks of use with the XOTrainer, 72% experienced an increase in triceps thickness, with the dominant arm  and but a more modest 44% experienced a positive change in the non-dominant arm. 


Complete Text


Obesity is a disease characterized by a high degree of adiposity and is associated with a wide variety of adverse health effects. For an individual to maintain a stable bodyweight, their calorie (energy intake) must match their energy output. Finding and developing sustainable ways to increase calorie expenditure and/or decrease calorie consumption can be of great benefit to the health of the population. Some individuals either cannot, or have no desire to perform regimented exercise sessions. An alternative is to find ways in which individuals can achieve positive health benefits whilst performing their normal daily routine. The purpose of the proposed investigation is to test the efficacy of a non-invasive, exoskeletal device to enhance health-related fitness (muscle strength/endurance and body composition) of University employees who spend a significant amount of time in a sedentary (inactive) state for most of the day. The current investigation utilized a repeated measures design, where the dominant upper limb was used as the experimental limb (wears the device), while the non-dominant limb did not wear the device. Only one treatment was utilized (the exoskeletal resistance training device, similar to a brace worn after surgery).  


Obesity is a disease characterized by a high degree of adiposity and is associated with a wide variety of adverse health effects including hypertension, type II diabetes and cancer (Kopelman, 2007). Within the US between 2015-2016, obesity prevalence was found to be 39.8% in adults and 18.5% in youths (Hales et al., 2017). Weight management from a thermodynamics standpoint is a relatively simple case of matching calories consumed vs calories expended. However, simples does not mean easy and the biological and psychological factors that underpin the regulation of these factors are complex (Friedman, 2009). Finding and developing sustainable ways to increase calorie expenditure and/or decrease calorie consumption can be of great benefit to the health of the population.

Performing a regimented exercise bout (i.e. going for a run, lifting weights etc) can be one such way to increase an individual’s daily calorie expenditure. Another is to increase the difficulty of movements that an individual is already performing over the course of their day or during their work day. Some individuals may either be unable (i.e. injury, chronic pain etc) or unwilling (i.e. time barrier) to perform a regimented bout of exercise. However, it is important for these individuals to maintain energy balance and body composition within a healthy range.

Wearing a variable resistance exoskeletal device has been marketed to improve muscle strength and size and reduce body fat mass. The principal is that by wearing this device under clothing throughout the day, every activity involving elbow flexion or extensions will become more difficult. This increased difficulty will then translate to a strengthening of the muscles involved, as well as an increased calorie expenditure (leading to body fat loss). However, it has not yet been determined whether these claims are true and whether a device of this nature is able to provide a high enough intensity to elicit these changes.

Therefore, performing a controlled trial to evaluate these claims is warranted. If this device can achieve these outcomes, then it may have application for improving health and/or fitness in some populations.


  • Subjects

Participants were included in the current investigation if they were between 30-64 years of age.  They also had to be sedentary (not currently participating in any exercise outside of activities of daily living), non-hypertensive (unless controlled by medication), and free of any orthopedic issues/injuries.  Participants were excluded if they have uncontrolled hypertension, unregulated diabetes, or any musculoskeletal injuries or orthopedic complications, or are below 30 years of age or above 64 years of age.  Participants were contacted in two ways: via a University-wide email from the OU Wellness program or from posted study fliers to be hung in various buildings around campus.  The flier contained the contact info for the PI (Dr. Jay Campbell) and the sub-investigator (Joel Prowting) in the form of cell phone number and OU email.

  • Measures and Procedures

During the investigation, following the consent process and study inclusion, all participants were asked to complete a 8-week trial involving the performance of everyday activities while wearing a novel, exoskeletal resistance training device on the upper and lower areas of their dominant arm. The non-dominant arm served as the control for each participant. Initial performance and health related fitness testing (pre-test) occurred prior to the start of the 8-week trial period.  Following 8 weeks, all performance and health related fitness measurements were replicated (post-test).  All study tasks are outlined for each visit, as well as, the study metrics (dependent variables) that were assessed. They are as follows:

Visit 1 (Familiarization, risk assessment, medical history, informed consent, pre-testing for all health-related fitness metrics).  Approximate time will be 2.5 hours at the Department of Health and Exercise Science (face to face meeting).  The tasks to be completed are as follows:

  1. Informed consent – each participant had the study purpose, study protocol, risks, benefits, protections for privacy and confidentiality, and explanation of the volunteer nature of participation explained to them, along with any questions they may have had regarding the consent form. Once the potential participant was fully clear about their desire to participate, they signed the informed consent form prior to any collection of data.
  2. Risk and physical activity assessments – participants completed the Physical Activity Readiness Questionnaire (PAR-Q), the International Physical Activity Questionnaire (IPAQ), and the AHA/AMA Medical History Questionnaire in order to ascertain the sedentary status of the potential participant, the relative risk related low to moderate physical activity, as well as, the need for physician’s clearance prior to participation in the study.
  3. Height, weight, age, occupational status, resting blood pressure, and resting heart rate were obtained/measured
  4. Body composition assessment – body composition (fat-free vs. fat mass) was assessed using the bioelectrical impedance which required only that the participant lie still for 20 while a low voltage current was passed from the upper to lower extremity. Participants were asked to be well hydrated to improve accuracy of the test
  5. Waist, hip, and upper arm circumference determination – these measurements were measured to assess regional changes in body composition
  6. Muscle thickness changes at the biceps and triceps – ultrasound (non-invasive) sensors were used to determine initial muscle thickness of the biceps and triceps musculature for determination of muscle hypertrophy (growth) as a result of using the exoskeletal device over the duration of the study
  7. Muscle strength assessment of the upper arm – following 2 familiarization attempts, participants performed 3 repetitions on a maximal isokinetic (speed is regulated by machine) utilizing an elbow flexion and elbow extension movement at 60 degrees/sec (low speed) and 180 degrees per sec (high speed) for determining initial muscular strength
  8. Device fitting and adjustment – Participants were fitted for the exoskeletal device and shown how to properly align the device to the arm. All resistances to be used were determined from the isokinetic strength assessment and marked for the participants to help ensure proper intensity of activity.

Visit 2 – (45 minutes, mid-test) Measurements for weight, resting blood pressure, resting heart rate, body composition, waist/hip/upper arm circumference, muscle thickness, muscle strength were repeated following 8 weeks of treatment administration (wearing the exoskeletal device)

  • Statistical Methods and Data Analysis

The current investigation was a randomized (random selection), controlled trial.  It incorporated a repeated-measures, between (exercise arm vs. control arm) and within (across time) group design.  Statistical power was set at a 1-ß = 0.8, effect size of 0.5, and a priori significance was set at 0.05.  This assessment was performed using G*Power 3 (see reference) software.  A total of 54 individuals responded to the research advertisement, with 31 participants scheduling an initial testing session.  A total of 13 participants dropped out of the study (11 because of time conflicts, 1 for a family situation, and 1 who did not want to continue), resulting in 18 participants who completed the full 8-week study.  All group statistics were performed on percent change from baseline to account for high level of variability expected amongst participants.  All data are presented accordingly as mean ± 1 standard error.  Where individual differences/responses to wearing the device were of interest, data is presented based on proportions.


Subject physical characteristics are presented in Table 1.  No statistically significant differences were observed for relaxed arm circumference, flexed arm circumference, total work during extension or flexion at either speed (600/s, 1800/s) from pre to post device use in either the dominant or non-dominant arm.  However, a statistically significant interaction effect (p=0.038) for time by condition was observed for biceps thickness.  This finding indicates that although, no group mean difference existed at the beginning of the study between the dominant and non-dominant arm among participants, post testing demonstrated a significantly greater increase in the dominant arm (the arm the device was worn upon) following the 8-week use period compared to the non-dominant arm (the arm no device was worn upon).  Main effects for time were also observed in triceps thickness (increased; p=0.045), peak extension torque (increased; 600/s p=0.044, 1800/s p=0.022), and average power output during extension (increased; 600/s p=0.004, 1800/s p=0.001).  There were no statistically significant interaction or main effect for time in total work during extension or flexion at any speed nor average power during flexion at any speed.  Lastly, no main effect for group was observed at any point for any of the experimental variables.  Mean values plus the standard error of the estimate (SEE) for all isokinetic dynamometer muscle performance measures and ultrasound measures of tissue thickness are presented in Table 2. 

Table 1.  Mean (SD) subject physical characteristics (n=18).
Age(yrs)           Ht (cm)             Wt (kg)             BMI (kg/m2)
42.4                 169.8               78.9                 27.5
(4.9)                 (9.56)               (15.33)             (5.8)


BMI = Body Mass Index

Table 2.  Summary of statistically significant differences pre to post for the Dominant (device) Arm and Non-Dominant (no device) Arm

(* Indicates statistically significant differences at p ≤ .05 level for time;
** Indicates group differences ; 
# indicates a significant interaction;
All data expressed as mean ± SEE). 

                                  Dominant Arm                       Non-Dominant Arm



                             Pre                     Post                   Pre                  Post               

Relax Arm Circ   33.14±1.09          32.98±0.97        33.03±1.02       32.81±0.98   

Flex Arm Circ      33.60±1.04          33.88±0.96       33.44±1.02       33.68±0.93   

*#BicepsThickness  2.1±0.13          2.28±0.12      2.13±0.14        2.12±0.11   

*Triceps Thickness  2.9±0.20          3.14±0.16      2.84±0.19        2.88±0.19   

*PT Ext 600/s      37.6±3.10            40.95±4.03     38.50±3.31      41.09±3.79   

PT Flex 600/s      39.4±3.54            40.37±3.64      37.14±3.29     37.89±3.14

*PT Ext 1800/s     29.1±2.17            32.58±2.99     29.85±2.37     32.43±2.48

PT Flex 1800/s     32.3±2.94            33.05±3.04     30.89±2.84     30.72±2.78

TW Ext 600/s       131.7±11.91       138.42±11.45   143.08±12.26  145.64±13.30  

TW Ext 1800/s     95.2±9.60           105.99±10.53   101.97±8.83   107.00±10.05

*Avg. Pow Ext 600/s 26.76±2.55    31.41±3.33        28.69±2.54     30.76±3.12   

Avg. Pow Flex 600/s 30.06±3.07    30.73±2.94       28.17±2.57      29.32±2.72

*Avg. Pow Ext 1800/s 47.40±5.08   57.21±6.47       49.76±5.08      55.77±5.85

Avg. Pow Flex 1800/s 52.29±6.51   53.87±6.97      49.19±5.65      50.95±6.70


Circ = Circumference, Ext = Extension, Flex = Flexion, 0/s = degrees/second, PT = Peak Torque in Newton-meters, TW = Total Work in Joules, Avg. Pow = Average Power in Watts

In Figures 1-5, the percent change is presented as a comparison of the relative change between the arm utilizing the device (dominant) and the other arm that did not (non-dominant arm) for arm circumference, muscle thickness, peak extension/flexion torque, total work during extension, and average extension/flexion power output.

Figure 1.  Percent Change from Pre to Post Testing for Relaxed and Flexed Arm Circumference

Figure 2.  Percent Change from Pre to Post Testing for Biceps and Triceps Muscle Thickness

Figure 3.  Percent Change from Pre to Post Testing for Extension & Flexion Peak Torque

Figure 4.  Percent Change from Pre to Post Testing for Extension Total Work

Figure 5.  Percent Change from Pre to Post Testing for Extension & Flexion Average Power 


Based on the findings of this study a few key points emerged.  The XOTrainer appears to provide a reasonable stimulus for increases in muscle thickness, peak torque during extension at both high speed and low force, as well as low speed and high force, as well as average power outputs during both conditions of speed and force.  Of note, is the bias of the device toward improving the extension phases of upper arm movement.  This may, in part, be explained by the bias towards “pulling” in most activities of daily living versus “pushing”.  This is finding may be of key interest to populations at risk for falling since any improvement in extension capacity may allow an individual to “catch” themselves and better decelerate the body following a loss of balance or fall forward.  Additionally, if there is in fact a tendency for sedentary individuals to have a diminished capacity to extension, the use of the device may provide an increase ease for activities of daily living or find a key market in the physical therapy sector, immediate post-op following elbow surgery.  The capacity of the device to increase muscle thickness (an indicator of some level of muscle hypertrophy) is also of interest since sarcopenia with aging and atrophy from disuse have both been shown to be negative risk factors related to overall health and the capacity for physical activity.  As with any modality, we must temper inferences made from group mean statistics related to its universal ability to be effective at eliciting positive results in all individuals.  The participants in the current study were motivated to wear the device, despite subjective reports in some cases of discomfort or difficulty with donning the device.  All participants were active participants in the University’s wellness program and received health behavior points as a result of participation.  Participants were asked to wear the device 4 hours or more during the typical work week, and this time commitment may not be indicative of typical wear patterns among the typical customer who purchases this device.  Additionally, in the current investigation, individuals wore the device on their dominant arm and the non-dominant arm was used as the control, despite the awareness by the investigators that the potential for a “cross-education” effect to be present at the completion of the study.  Cross-education is a phenomenon in which exercise on one (ipsilateral) side of the body elicits a concomitant increase in capacity on the opposite (contralateral) side of the body.  Since increases in the non-device arm were observed, a higher level of control would be used in any follow-up studies.  This was not a possibility in the current investigation due to budgetary restrictions.  With a true control group who did not wear the device, continued normal activities over the 8-week period, and was then measured pre and post, the investigators could more effectively draw inferences from both the group and individual changes observed.  Lastly, of additional interest to the device’s manufacturer, are the subjective observations shared by the study participants from the post-study survey.  In general, the participants rated the “comfort” of the device as “good” and the “ease of use” of the device as good-very good.  Of the 18 participants who completed the study, 12 indicated that using the device promoted other healthy behaviors such as improved nutrition, improved sleep/rest/recovery, increased physical activity throughout the day, and/or enhanced mood and positive outlook.  Eleven of the participants indicated that they would continue to use the device after completion of the study.  The investigators used great caution to not positively or negatively influence the participants in their responses to the questionnaire.   It was explained to the participants that the investigators held no business or personal interest in the device ratings, that all honest feedback would be used to improve the overall effectiveness and usability of the device.  The investigators left the area while the participants completed the questionnaire. 


It appears the XOTrainer has the capacity to improve the musculature favorably, both anatomically and functionally through its daily use.  With many people in general stating “time” as one of their most fervent barriers to starting/adhering to an exercise program, the XOTrainer may provide a reasonably cost-effective and easily transportable solution for increasing upper arm muscle quality and fitness capacity.  The major limitation is that the device targets only the upper arm (biceps/triceps).  The true value of the device would be most realizable in either a sedentary population (similar to the one used in the current investigation) and/or during the immediate (first few weeks) in the post-surgical patient.  It would be our advice to develop a lower body (knee/hip) companion device that would specifically be targeted toward the post-ACL repair therapy patient.  Due to the concentric only nature of the XOTrainer, this would allow for tension to be placed through the newly healing ligament without the excessive stress of the eccentric portion of a muscle contraction.  Mild tension has been shown in recent literature to help promote improved tissue healing/growth in the early post-operative period versus non-tension with rest only.


  • Hales, C. M., Carroll, M. D., Fryar, C. D., & Ogden, C. L. (2017). Prevalence of obesity among adults and youth: United States, 2015-2016. US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics.
  • Kopelman, P. (2007). Health risks associated with overweight and obesity. Obesity reviews, 8(s1), 13-17.
  • Faul, F., Erdfelder, E., Lang, A.-G., & Buchner, A. (2007). G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behavior Research Methods39, 175-191

Appendix – Results from Post-Study Questionnaire

Subject ID


Ease of Use

Usage Time in Hours

Other + Actions (see Key below)*

Likelihood of Continuing Use

Respondent 1 95 92 2-3 3 90
Respondent 2 78 72 2-3 3 70
Respondent 3 60 75 4+ 3 90
Respondent 4 60 70 1-2 3,4 50
Respondent 5 85 90 4+ 0 75
Respondent 6 85 90 4+ 0 75
Respondent 7 40 90 3-4 3,5 50
Respondent 8 70 90 2-3 3 30
Respondent 9 60 40 3-4 0 30
Respondent 10 70 80 2-3 3 90
Respondent 11 85 85 3-4 3,4 70
Respondent 12 70 90 4+ 1,2,3 1
Respondent 13 65 82 3-4 0 1
Respondent 14 60 46 4+ 0 1
Respondent 15 10 30 3-4 0 1
Respondent 16 60 90 1-2 3 60
Respondent 17 40 50 4+ 3,4 20
Respondent 18 70 80 3-4 1 65
Mean 64.6 74.6 48.3
StDev 18.5 19.2
  1. 31.2


      0. = no health related behaviors were improved

  1. = improved nutrition
  2. = improved sleep/rest/recovery
  3. = increased physical activity throughout the day
  4. = enhanced mood and positive outlook
  5. = improved self-image

Note, the interesting results are that the un-XOTrained arm benefited.  This is an affect of sympathetic body learning.  The body will improve and  strengthen surrounding and balancing muscles to compensate for the strengthening of another body part.  Also, as the training arm gets tired, we tend to use our other arm more.