1. SKELETAL ADAPTATIONS AFTER 16-WEEKS OF HIGH-INTENSITY FUNCTIONAL TRAINING.
W. Hoffstetter, A. Box, H. Mimms, P. Serafini, M. Smith, B. M. Kliszczewicz, Ph.D, G. Mangine, Ph.D, Y. Feito Ph.D, FACSM,
Department of Exercise Science and Sport Management, Kennesaw State University
ABSTRACT
Introduction: High-Intensity Functional Training (HIFT) has recently gained popularity due to its limited time commitment and purported positive physiological effects. PURPOSE: We sought to examine if gender played a role in skeletal mass adaptations in active adults after 16-weeks of HIFT. METHODS: Nine men (34.2 ± 9.12 years, 1.78 ± 0.05 m, 91.5 ± 17.7 kg) and 17 women (36.3 ± 7.84 years, 1.63 ± 0.07 m, 68.5 ± 12.8 kg) with CrossFit® training experience completed 16-weeks (2 – 5 sessions ∙ wk-1) of HIFT. Within two weeks prior to training, pre-testing (PRE) measures of bone mineral density (BMD) and bone mineral content (BMC) were measured using Dual-Energy X-Ray Absorptiometry (DXA). Post-testing (POST) was completed following 16-weeks of training. RESULTS: Repeated measures analysis of variance did not reveal any significant interactions between the measures. Paired-samples t-tests showed a significant decrease in BMD (PRE: 1.24 ± 0.16 g/cm2, POST: 1.09 ± 0.27 g/cm2; p < 0.001), and an increase in BMC (PRE: 2,855.7 ± g, POST: 2,869.2 ± g; p = 0.039) for the entire group. CONCLUSION: It appears that a 16-week HIFT program is a suitable exercise modality to increase BMC. However, we believe the length of our study may not be suitable to positively influence BMD. Future studies should consider longer interventions and controlling for total work volume.
PURPOSE
The purpose of this study was to examine if gender plays a role in skeletal adaptation within a group of relatively active adults.
RESULTS, Cont’d
Figure 1. Changes in Bone Mineral Density Following 16-Weeks of HIFT
METHODS
A total of 26 participants completed the study and performed pre and post measurements.
Prior to each laboratory visit participants were asked to avoid eating or consuming any beverage other than water four hours before testing, 12-hours for caffeine before and 24-hours for alcohol.
Additionally, Participants refrained from any exercise at least 12-hours prior to testing.
Training included participation in HIFT workouts with a focus on general physical preparedness (GPP) a minimum of twice a week for 16-weeks.
Testing sessions entailed both pre and post data collection of variables of interest.
Testing Procedures
Bone mineral density (BMD; g/cm2), and mineral content (BMC; g), were obtained via Dual-Energy X-Ray Absorptiometry (DXA) (iLunar; General Electric, CT).
Statistical Analysis
Repeated measures analysis of variance (ANOVA) was used to examine gender × time interaction for each measure of BMD and BMC.
Paired-sample t-test was used to examine changes in BMD and BMC across the 16-week intervention.
P < 0.001
Figure 2. Changes in Bone Mineral Content Following 16-Weeks of HIFT
Table 1: Participant Characteristics (Mean ± SD)
Males
Females
Weight (kg)
91.53 ± 17.66⁺
68.48 ± 12.84
Age (yrs)
34.2 ± 9.12
36.3 ± 7.84
Height (m)
1.78 ± .05⁺
1.62 ± .07
BMD (g/cm2)
1.358 ± .128⁺
1.19 ± 0.08
BMC (g) ± ±
INTRODUCTION
The American College of Sports Medicine (ACSM) suggests that adults who participate in weightlifting (and other load-bearing exercises) have higher bone mineral density (BMD) and bone mineral content (BMC) than adults who engaged in other physical pursuits, such as running, or cycling (3).
Resistance training, leads to improvements in BMD/BMC as long as the exercise is performed at an adequate intensity to stimulate hypertrophy (2). Resistance-training programs of higher loads and intensities have demonstrated significant improvements in bone metabolism compared to traditional resistance training (4,5).
In recent years, a new modality of exercise known as high-intensity functional training (HIFT) has emerged. HIFT is a dynamic method of exercise combining aerobic and musculoskeletal conditioning with a focus on functional (multi-joint) movements (1).
CONCLUSIONS
HIFT appears to be a suitable modality to improve BMC.
Although decreases in BMD were seen, the duration of the study may have been a limitation. Therefore, future studies of longer duration may be needed in order to assess HIFT’s effect on BMD.
⁺ = P < 0.05
RESULTS
Participant characteristics are shown in Table 1.
Repeated measures ANOVA did not reveal any significant group × time interactions for either BMD or BMC.
Paired-sample t-tests revealed a statistically significant decrease in BMD (PRE: 1.24 ± 0.13 g/cm2, POST: 1.09 ± 0.27 g/cm2; P < 0.001) (Figure 1), and a statistically significant increase in BMC (PRE: 2,855.7 ± g, POST: 2,869.2 ± g; P = 0.039) for the entire group (Figure 2).
References
Heinrich et al. High-intensity compared to moderate intensity training for exercise initiation, enjoyment, adherence, and intentions: an intervention study. BMC Public Health :789.
João et al. Effect of 16 weeks of periodized resistance training on strength gains of powerlifting athletes. Journal of Exercise Physiology, 2014; 17(3):  
Kohrt, W. (n.d.). American College of Sports Medicine Position Stand: Physical activity and bone health. Medicine & Science in Sports & Exercise, 2004; 36(11):
Stengel, S. Power training is more effective than strength training for maintaining bone mineral density in postmenopausal women. Journal of Applied Physiology 2005;  
Walters et al. Case Study: Bone Mineral Density of Two Elite Senior Female Powerlifters. Journal of Strength and Conditioning Research, 2014; 1-1.
The authors have no conflict of interest. This project was not funded by any external sources. The use of trade names and commercial sources in this document is for identification purposes only and does not imply endorsement by the authors. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
Disclaimer
Presented at the 63rd Annual meeting of the American College of Sports Medicine
June 2016 – Boston, Massachusetts.