EFFECT OF WEIGHT SUPPORT ON TIBIAL ACCELERATIONS DURING A LOWER-BODY POSITIVE PRESSURE TREADMILL CADENCE CONTROLLED RUN Brendan J. Rickert, Matthew F. Moran, Beau K. Greer Department of Physical Therapy and Human Movement Science, Sacred Heart University, Fairfield, CT Contact Information: rickertb@sacredheart.edu ABSTRACT CONCLUSIONS PARTICIPANTS The accelerometer was placed on the non-dominant leg (Figure 2). A second testing period (n=2) was completed three weeks after the first testing period to examine the reliability of the testing protocol. Running in a lower-body positive pressure treadmill (LBPP-TM) is utilized for athletes to maintain fitness while recovering from tibial stress fracture. Previous investigations report that step rate is linearly related to level of body weight (BW) support and tibial accelerations (TA) is not significantly reduced until <70% BW as compared to normal values. PURPOSE: The purpose of this study was to investigate the relationship between BW support level on a LBPP-TM and TA during a cadence-controlled run. METHODS: Nine competitive male runners (24.0±6.9 yo; 61.4±6.6 kg) volunteered and completed the study. Following a 10-minute familiarization run on a LBPP-TM each subject started at 100% BW and ran at a consistent velocity for three minutes during each of nine stages which progressively decreased at 5% intervals until 60% BW. A metronome was set to match the natural cadence of the individual attained during the familiarization run in order to control cadence. Two participants were excluded from the results as they were unable to match cadence within ±1% as determined through data processing. During the last 30 seconds of each stage, TA was measured via a skin-mounted uniaxial accelerometer (PCB Piezotronics; Depew, NY) attached to the lower third of the anterior tibia; data were recorded via Qualisys Track Manager Software (Qualisys; Gothenburg, SWE) and processed with custom-written MATLAB code (MathWorks; Natick, MA). Wilcoxon Signed Ranks tests were utilized to compare TA differences between BW levels. Statistics were processed with PASW software (IBM; Armonk, NY). RESULTS:. TA was significantly reduced (p<0.05) for every 10% reduction (100% vs. 90%, 90% vs. 80%, 80% vs. 70%, 70% vs. 60%) in BW (11.8±3.1g, 10.6±2.1g, 9.7±1.8g, 8.6±1.2g, 7.2±0.4g, respectively). There were no significant differences in step rate (p = 0.995; 177.0 ± 0.1 steps/minute) between any BW level. CONCLUSION: When controlling for cadence, tibial accelerations were significantly reduced as BW support was increased on a LBPP-TM. These results reflect the importance of maintaining normal temperospatial mechanics when running at BW levels < 100% which were not controlled for in previous studies. Clinicians should consider the use of a metronome to control cadence while running in a LBPP-TM for runners recovering from tibial stress fracture. Nine collegiate cross-country team runners volunteered for this study. All subjects were free of lower-extremity injuries for at least six months prior to the study and had a minimum of four years of running experience. All subjects were weighed measured for height, and self-reported their leg dominance and current training history (Table 1). Leg dominance was determined by asking each subject their preferred kicking leg. All experimental procedures were approved by the Sacred Heart University Institutional Review Board . Subjects were informed of the experimental procedures and all granted their informed consent. When controlling for cadence, tibial accelerations were significantly reduced as BW support was increased on a LBPP-TM. These results reflect the importance of maintaining normal temperospatial mechanics when running at BW levels < 100% which were not controlled for in a previous investigation in this lab11. Table 2: Testing Protocol   Warm up Stage 1 2 3 4 5 6 7 8 9 BW % 100% 95% 90% 85% 80% 75% 70% 65% 60% Duration (Min) 10 PRACTICAL APPLICATION The AG TM is a new tool in performance enhancement and rehabilitation. Clinicians should consider the use of a metronome to control cadence while running in a LBPP-TM for runners recovering from tibial stress fracture. When prescribing BW levels to start at, the patient should experience no pain while running. As pain decreases outside of the AG TM, BW support should also decrease until the patient is able to run at 100% BW asymptomatically. It is important to note from a training perspective that HR decreases with BW and adjustments in speed and/or incline may need to be made in order to receive similar benefits of training outside of the AGTM. Table 1: Subject data RESULTS Height (m) 1.76 ± 0.2 Mass (kg) 61.4 ± 6.6 Age (years) 24.0 ± 6.9 Running Experience (years) 8.6 ± 3.1 Self-Reported Running Miles Per Week 49 ± 16 Leg Dominance (Right Leg) N= 9 Wilcoxon Signed Ranks tests were utilized to compare TA differences between BW levels. TA (Figure 3) was significantly reduced (p<0.05) for every 10% reduction (100% vs. 90%, 90% vs. 80%, 80% vs. 70%, 70% vs. 60%) in BW (11.8±3.1g, 10.6±2.1g, 9.7±1.8g, 8.6±1.2g, 7.2±0.4g, respectively). Similarly, Peak to Peak (PP) (Figure 4) was also significantly reduced (p<0.05) for every 10% reduction in BW. Heart rate (HR) had significant differences between all conditions (p<0.05) as BW decreased as did HR. There were no significant differences in step rate (Figure 6) (p = 0.995; 177.0 ± 0.1 steps/minute) between any BW level. REFERENCES EXPERIMENTAL METHODS 1. Alter-G. Alter-G Anti-Gravity Treadmill. Freemont, CA. 2012. Available at: http://www.alter-g.com/ 2. Mizrahi J, Verbitsky O, Isakove E. Fatigue-related loading imbalance on the shank in running: a possible factor in stress fractures. Annals of Biomedical Engineering. 2000 28.463-469. 3. Derrick TR, Hamill J, Caldwell GE. Energy absorption of impacts during running at various stride lenghs. Medicine & Science in Sports & Exercise. January 1998. 30(1) 128-135. 4. Hamill J, Derrick TR, Holt KG. Shock attenuation and stride frequency during running. Human Movement Science. 1995. 14. 45-60. 5. Milner C, Ferber R, Pollard C, Hamill J, Davis I. Biomechanical Factors Associated with Tibial Stress Fracture in Female Runners. Medicine & Science In Sports & Exercise. February 2006;38(2):323-328. 6. ACSM’s Guidelines for Exercise Testing and Prescription: Eight Edition. 2010. China. 7. Moran, MF, Rickert BJ: Effect of Body Weight Support on Spatiotemporal Running Mechanics. Presented at ACSM Annual Meeting, San Francisco, May 2012. 8. Kim B. Ground Reaction Forces and Bone Parameters in Females with Tibial Stress Fracture. Medicine & Science In Sports & Exercise. March 2004;36(3):397-404. 9. Cavanagh PR and Lafortune MA. Ground reaction forces in distance running. Journal of Biomechanics. 1980. Vol. 13, 397-406. 10. Figueroa MA, Manning J, Escamilla P. Physiological Responses to the AlterG Anti-Gavity Treadmill. International Journal of Applied Science and Technology.2011. Vol 1; 6. 11. Rickert BJ, Moran MF, Greer BK. Tibial Acceleration in Distance Runners in reduced Body Weight Conditions. Presented at the NSCA National Conference, Las Vegas, July 2013 All subjects wore their own training shoes and did not run on their respective testing day. Each data collection session started with a 10-minute warm-up on the AG TM at 0% incline and 100% BW. This 10-minute run was intended to acclimatize the participant to the AG TM as well as to determine a speed that was associated with 75% of their estimated maximum heart rate [ (206.9-(0.67x age) x 0.75)6 ] as well as determine normal BW cadence. After the warm-up, the subject ran at the same speed and cadence throughout each of the nine testing stages (Table 2). Runners had to match their cadence through an audible metronome. Each stage lasted 3-min and BW percentage was decreased 5% at the end of each stage. BW was not randomized due to a previous finding that subjects who went from reduced BW to 100% BW had higher rate of perceived exertion (RPE) and HR at the same BW conditions when compared to the group of subjects that decreased unloading.7 INTRODUCTION Twenty-four to 65% of all runners report a running-related injury (RRI) every year.2 Runners experience ~2.5 times their body weight (BW) upon impact during the stance phase of running.4 Fifty percent of all stress fractures occur in the distal end of the tibia.5 Typically, a tibial stress fracture requires 4-6 weeks of recovery time before training can resume.8 The AlterG treadmill (AG TM) artificially reduces BW through differential air pressure (DAP).1 For rehabilitation, DAP TM may have beneficial outcomes because they reduce ground reaction forces, muscular activity, and metabolic cost.9,10 A previously investigated study found no relationship between the level of BW unloading and tibial acceleration (TA).11 It is important to note that cadence decreased with decreasing BW in that study which may alter TA. The purpose of this study was to investigate the relationship between the level of BW in an AG TM and TA while controlling for cadence. Figure 2: Accelerometer in its housing chamber fixed to the tibia Figure 3: Mean Tibial Acceleration Figure 4: Mean Peak to Peak Tibial Acceleration Figure 1: AlterG Treadmill (AG TM) ACKNOWLEDGMENTS Thank you to Dr. Anna Price for statistical analysis assistance. Figure 5: Mean Heart Rate Figure 6: Mean Stride Rate Presented at the 61st Annual Meeting of the American College of Sports Medicine (Orlando, FL)