Background
Whole-body vibration (WBV) has been suggested as a form of physical training since the ‘60s, when NASA astronauts required a method of exercise to prevent muscle atrophy in a zero-gravity environment (Abercromby et al., 2007). It has been suggested that this training can elicit advantages for individuals who may have physical constraints or inability to exercise on a regular basis (Kilebrant et al., 2015). WBV is currently easily available, but the extent to which it imitates physical exercise is unclear. Well established universal benefits of exercise include improved insulin sensitivity, adipocyte or fat quantity, and muscle mass. A study by McGee-Lawrence et. al, 2017 compared exercise versus WBV, and found that WBV produced similar effects as treadmill exercise with respect to improved insulin sensitivity, better glycemic control, decreased muscle atrophying, and increased cortical bone mass from increased osteocalcin. It is interesting to note that some of these characteristics are intertwined, since adipocyte density is linked to insulin sensitivity (Guilherme et al., 2008) as well as skeletal health (Muruganandan et al., 2018). Excess adipose tissue can also cause lipid overload, leading to more insulin resistance and deposits on major organs - which may cause diseases like hepatic steatosis. In addition, excess adipose tissue puts a toll on bone growth, which limits the release of osteocalcin. Osteocalcin is essential for the body because it not only acts as a hormone to promote insulin production, it also triggers the release of adiponectin which improves insulin sensitivity.
How was the McGee-Lawrence et.al, 2017 study performed?
They compared 5-week-old male wild-type (WT) and 5-week-old male diabetic (db/db) mice that had been treated with either daily treadmill exercise (TE) or WBV. They also included a group of sedentary diabetic mice (SED). Either WT or db/db mice were assigned per condition (SED, WBV, or TE), with n = 14 to 16 per condition. Each genotype had 6 to 8 mice per condition (n = 6 to 8). WBV was performed for 20 min/day for 12 weeks at 32Hz and 0.5g acceleration with a motor (Mavilor BLT-055 through Automotion Inc.) mounted to a baseplate and a 500g accelerometer (model 352A10, PCB Peziotronics) , and TE (Columbus Instruments Animal Treadmill Exer 3/6) was performed for 45 min/day for 12 weeks.
Approach
Glucose Tolerance Testing
Glucose levels were tested with a glucometer and Freestyle Lite test strips after being injected with 1.0g/kg glucose in sterile saline. Insulin tolerance testing was performed by using a glucometer as well, after being injected with 0.5 IU/kg insulin.
Lipid Quantification
Serum chemistry was quantified with a robotic analyzer while cholesterol, triglycerides, and LDL were quantified with assay kits.
Tissue
Histology of adipose tissue was done with tissue from the subcutaneous region, and adipocyte size was quantified with ImageJ. Histology of lower leg muscles were quantified also with ImageJ. Hepatic lipid content was measured by weighing liver samples, homogenization and chloroform extraction of lipid, and subsequent quantification by comparing to liver weight.
Bone Analysis
Cortical bone was analyzed by scanning each femur with a microCT system, to quantify bone thickness and area.
Results
Muscle Tissue and Weight
Overall, WBV and TE reduced weight gain in diabetic (db/db) mice by 7 ± 4% for WBV and 16 ± 4% for TE treatments. MBV also reduced weight gain in WT mice by 11 ± 1% and TE by 15 ± 1% (P<0.01). WBV and TE also increased muscle fiber diameter in db/db mice; in db/db SED vs db/db WBV (P<0.01) by 20 ± 2% (P<0.01), and in the db/db SED vs. db/db TE by 28 ± 2% (P<0.01).
Adipocyte Hypertrophy
TE and WBV reduced size of only visceral white adipose tissue in db/db mice compared to db/db SED (P<0.01). White adipose tissue was decreased with TE by 17 ± 13% and decreased with WBV by 17 ± 6%.
Glycemic Control and Insulin Resistance
TE and WBV reduced insulin concentration 120 minutes after intraperitoneal administration of 1.0 g/kg glucose, resulting with a 50% decrease in ng/mL of insulin. It also restored insulin sensitivity, with a 38± 10% decrease in glucose concentration (mg/dL) with WBV treatment, and a 50 ± 2% decrease in glucose concentration with TE treatment (P<0.05). TE and WBV exerted similar effects on glucose metabolism overall.
Skeletal Response
WBV or TE increased serum osteocalcin in db/db mice compared to SED db/db (P<0.01), with a 90 ± 2% increase in serum osteocalcin with WBV and a 100 ± 2% increase with TE. WBV did not normalize bone mineral density in db/db mice, but TE did (P<0.01). TE increased bone mineral density (BMD) by 1.5%, while WBV treated mice showed a 1.5% decrease in BMD.
Concerns
The number of mice assigned for each specific condition is only 6-8 db/db mice and all the mice used in the study were only 5 weeks old. Age could potentially be a relative factor in influencing muscle tissue, insulin sensitivity, and skeletal health.
The current study only conducts WBV at 20-minute intervals which is likely to be too short to suggest correlations between leptin deficiency on bone mass and can only suggest an indirect relation based on osteocalcin production. The TE experiments were done for 45 minutes so the improved effects of the TE may be due to the longer duration of the exercise. Similar times for WBV and TE should have been investigated.
Conclusion
Whole-body vibration seems to produce positive effects comparable to those observed in regular exercise, but the extent of this relationship is still unclear. Insulin sensitivity is shown to increase, muscle mass is shown to increase as well as osteocalcin levels, but the effectiveness of this application to humans is still being investigated. For now, traditional exercise is likely our best bet, but a new well investigated and established method of WBV for those with physical limitations and stringent schedules is likely to be widely used soon.
Written by Roger Hsieh and edited by Aldrin Gomes.
References
Abercromby, Andrew & Amonette, William & Layne, Chuck & K McFarlin, Brian & Hinman, Martha & Paloski, William. (2007). Vibration Exposure and Biodynamic Responses during Whole-Body Vibration Training. Medicine and science in sports and exercise. 39. 1794-800. 10.1249/mss.0b013e3181238a0f
Da Jing, Erping Luo, Jing Cai, Shichao Tong, Mingming Zhai, Guanghao Shen, Xin Wang, Zhuojing Luo Mechanical Vibration Mitigates the Decrease of Bone Quantity and Bone Quality of Leptin Receptor-Deficient Db/Db Mice by Promoting Bone Formation and Inhibiting Bone Resorption Journal of Bone and Mineral Research 2016;31(9):1713-1724. doi:10.1002/jbmr.2837
Guilherme A, Virbasius JV, Puri V, Czech MP. Adipocyte dysfunctions linking obesity to insulin resistance and type 2 diabetes. Nat Rev Mol Cell Biol. 2008;9(5):367–377. doi:10.1038/nrm2391
Kilebrant, Sophie & Braathen, Gunnar & Emilsson, Roger & Glansén, Ulla & Söderpalm, Ann-Charlott & Zetterlund, Bo & Westerberg, Barbro & Magnusson, Per & Swolin-Eide, Diana. (2015). Whole-Body Vibration Therapy in Children with Severe Motor Disabilities. Journal of rehabilitation medicine. 47. 10.2340/16501977-1921
McGee-Lawrence ME, Wenger KH, Misra S, et al. Whole-Body Vibration Mimics the Metabolic Effects of Exercise in Male Leptin Receptor-Deficient Mice. Endocrinology. 2017;158(5):1160–1171. doi:10.1210/en.2016-1250
Shanmugam, Muruganandan & Govindarajan, Rajgopal & J. Sinal, Christopher. (2018). Bone Marrow Adipose Tissue and Skeletal Health. Current Osteoporosis Reports. 16. 10.1007/s11914-018-0451-y