1. Background
High-intensity interval training (HIIT) has been used as an alternative to traditional aerobic training (1).
HIIT is practical for many individuals due to the minimum time required when compared to traditional continuous endurance training. In the last few years a new variation of HIIT that combines high-intensity endurance training with varied and multiple-joint movements has become popular. High-intensity power training (HIPT) differs from traditional HIIT in that it does not include rest periods but it focuses on sustained high power output and resistance (2).
Depending on the age and fitness level of the subjects as well as the duration and intensity of the intervention; improvements of muscle mass, strength and VO2 max have been reported (3-5). In literature there are different studies that evaluated the effects of high-intensity sports on different aspects of body composition and health. In particular, it was concluded that HIPT is an effective training strategy to improve cardiovascular health, physical performance (6), basal metabolic rate and body composition (1).
Previously, in literature the high intensity training was compared with low to medium-intensity, with good results. Currently, there are no studies that compare various forms of training at high intensity. The aim of this study is to compare the effects of two high intensity training methods on body composition markers, muscle strength and basal metabolic rate.
2. Methods
2.1. Study Participants
We evaluated both male and female subjects, with a history of moderate training activity, from May 2014 to June 2015, at metabolic and body composition lab of the University of Pavia.
Fourty participants were recruited. Twenty participants received the high intensity power CrossFit training group voluntarily, the other twenty performed high intensity intermittent swimming training (controls).
The inclusion criteria were that participants must be aged above 18 years and below 45 years, available to complete all exercise sessions and with a previous history of moderate training, such as fitness or gym activity. Subjects were included in this study if they were physically active and healthy. A preliminary visit was conducted to detect the lack of inclusion criteria. Participants were excluded if they participated in regular physical high intensity training previously, and if they had unstable medical conditions such as cardiovascular disorders, musculoskeletal injury, and cardiopulmonary disorders that might affect the performance. Each athlete had given informed consent to participate in this research.
2.2. Instruments
2.2.1. Body Composition Markers
Body composition was measured by dual-energy X-ray densitometry (DXA) using a Lunar Prodigy DEXA (GE Medical Systems, Waukesha, Wisconsin). The in vivo coefficients of variation were 0.89% and 0.48% for fat and muscle mass, respectively. Free fat mass (FFM; in grams), % free fat mass (%FFM), fat mass (FM; in grams), % fat mass (%FM), android fat %, gynoid fat % were evaluated on the basis of total body scan data. Absolute DXA data were compared to previously established age- and sex-matched reference values (7).
2.2.2. Maximal Handgrip Strength Test
The handgrip strength of the dominant hand was assessed using a Jamar dynamometer (Sammons Preston, Mississauga, ON, Canada). Standard assessment procedures were followed as described in a previous study (8). Briefly, participants squeezed the dynamometer as hard as possible three times, and the highest grip-strength value was used for analysis. The inter- and intra-rater reliabilities of this test have been reported to be good to excellent (ICC = 0.94 - 0.98) in adults.
Figure 1.
Participant Flow Diagram
2.3. Training Protocol
Subjects participated in a high intensity training program three non-consecutive days (Monday, Wednesday and Friday) per week throughout the entire eight-week training period. All training was performed under the supervision of the principal investigators and trained HPL research assistants.
The CrossFit group utilized training for 60-minute sessions. Nine movements (i.e. air squat, front squat, overhead squat, press, push press push jerk, deadlift, sumo deadlift high pull, and medicine ball clean) were introduced in sessions 1 - 2. Remaining sessions included warm-up and stretching (10 - 15 minutes), instruction and technique practice (10 - 20 minutes), workout (5 - 30 minutes), and cool-down and stretching (5 minutes). Swimmers group completed session lasted 60 minutes and consisted of 20 60 seconds all-out free-style swimming (front crawl) intervals interspersed by 2 min of passive recovery after training principles previously described.
2.4. Resting Energy Expenditure
Resting energy expenditure (REE) was measured using a ventilated hood and open-circuit calorimeter (QUARK RMR, Cosmed, Rome, Italy). Before each evaluation, the device was calibrated to 95% O2 and 5% CO2. All subjects underwent the test in the morning after a 12-hours overnight fast. The subjects were instructed to avoid any intense physical activity during the 24-hours period before REE measurement. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were continuously measured for 25 minutes. The first 5 minutes were discarded to ensure adequate acclimation. The subjects were instructed to avoid hyperventilation, fidgeting, or falling asleep during the test.
2.5. Statistical Analysis
For each outcome, one-way ANOVA was performed for assessment differences between intervention groups at baseline. Analysis of covariance (ANCOVA) was performed using of covariate sex, percentage of fat mass, percentage of gynoid fat and fat mass in grams were used to compare crossfitter and swimmer over the time (i.e. mean differences between treatments over the time). The statistical package SPSS version 20 was used for statistical analysis (9). A value of P < 0.05 was considered statistically significant.
3. Results
Participant flow diagram is shown in Figure 1. Fifteen athletes received CrossFit training, and another fifteen athletes received swimming training. In either groups there were drop outs. The reasons were injuries, 5 among crossfitters and 2 among swimmers. Recruitment was performed from May 2014 to June 2015. The follow-up was 8 weeks.
Table 1 shows the baseline outcomes in both groups. There were no significant difference between-groups.
Nevertheless, as showed in Table 2, the between-treatment comparisons (over the time) by analysis of covariance (ANCOVA) demonstrated a significant effect of CrossFit. Between groups, data comparisons (pre-post intervention training) demonstrated a significant effect of CrossFit on gynoid fat (β = -1.42%; CI 95% -2.81; -0.03; P = 0.047), and suggestive but not significant variations in decreasing for total fat mass (β= -1427 g, CI 95%: -2861, 7,31; P = 0.051) and android fat (β=-2.64%, CI 95%: -5.36, 0.08; P = 0.056).
Table 1.Sample Characteristics at Baselinea
| Variable | Crossfitters (N = 10) | Swimmers (N = 13) | P Value | Total (N = 23) |
|---|---|---|---|---|
| Age, y | 33.10 ±9.826 | 30.69 ± 5.186 | 0.778 | 31.74 ± 7.460 |
| Weight, kg | 71.66 ± 19.134 | 68.88 ± 8.483 | 0.975 | 70.09 ± 13.821 |
| BMI, kg/m2 | 24.71 ± 4.291 | 22.86 ± 1.007 | 0.315 | 23.67 ± 2.994 |
| Arms free fat mass, g | 6.99 ± 3.043 | 6.67 ± 1.610 | 0.704 | 6.81 ± 2.287 |
| Legs free fat mass, g | 19.81 ± 6.673 | 20.11 ± 3.859 | 0.480 | 19.98 ± 5.135 |
| Free fat mass, g | 53.18 ± 16.557 | 54.0 ± 9.404 | 0.416 | 53.64 ± 12.681 |
| Fat mass, g | 15.80 ± 7.203 | 12.03 ± 4.412 | 0.167 | 13.67 ± 5.958 |
| Gynoid fat, % | 31.26 ± 11.183 | 24.91 ± 10.011 | 0.174 | 27.67 ± 10.779 |
| Android fat, % | 27.69 ± 11.090 | 25.67 ± 8.952 | 0.286 | 26.55 ± 9.750 |
| A/G ratio | 0.89 ± 0.239 | 1.08 ± 0.290 | 0.099 | 1.00 ± 0.281 |
| Tissue, g | 68.97 ± 17.962 | 66.02 ± 7.995 | 0.938 | 67.31 ± 13.004 |
| Free fat mass, % | 76.54 ± 9.052 | 81.47 ± 7.356 | 0.179 | 79.33 ± 8.323 |
| Fat mass, % | 23.46 ± 9.052 | 18.53 ± 7.356 | 0.179 | 20.67 ± 8.323 |
| Handgrip strenght (right), kg | 47.80 ± 13.935 | 48.92 ± 13.543 | 0.854 | 48.35 ± 13.739 |
| Resting energy exp., kcal | 1401.50 ± 440.66 | 1475.08 ± 264.72 | 0.343 | 1438.29 ± 352.69 |
aIn bold: P < 0.05.
| Variables | Pre - Training (Swimmers) | Post - Training (Swimmers)** | Pre - Training (CrossFit) | Post - Training (CrossFit)** | Mean Difference and CI 95% (Crossfitters Minus Swimmersc) | F | P Value |
|---|---|---|---|---|---|---|---|
| Weight, kg | 71.66 ± 19.13 | 69.70 ± 0.47 | 68.88 ± 8.48 | 68.10 ± 0.54 | -0.70 (-2.33; 0.92) | 0.84 | 0.372 |
| BMI, kg/m2 | 24.710 ± 4.291 | 23.29 ± 0.20 | 22.862 ± 1.01 | 23.54 ± 0.24 | 0.25 (-0.50; 0.98) | 0.49 | 0.493 |
| Arms free fat mass, g | 6995 ± 3043 | 6804 ± 131 | 6668 ± 1610 | 6757 ± 155 | -46.50 (-536.53; 443.54) | 0.04 | 0.843 |
| Legs free fat mass, g | 19810 ± 6673 | 20029 ± 247 | 20112 ± 3859 | 20248 ± 286 | 219.10 (-631.93; 1070,13) | 0.30 | 0.593 |
| Free fat mass, g | 53176 ± 16557 | 53548 ± 508 | 53999 ± 9404 | 54410 ± 590 | 861.19 (-909.08; 2631.46) | 1.06 | 0.318 |
| Fat mass, g | 15797 ± 7203 | 13229 ± 426 | 12025 ± 4412 | 11801 ± 492 | -1427.24 (-2861.79; 7.31) | 4.41 | 0.051 |
| Gynoid Fat, % | 31.26 ± 11.183 | 27.30 ± 0.41 | 24.91 ± 10.011 | 25.88 ± 0.48 | -1.42 (-2.81; -0.03) | 4.63 | 0.047 |
| Android fat, % | 27.69 ± 11.090 | 26.33 ± 0.74 | 25.67 ± 8.952 | 23.69 ± 0.88 | -2.64 (-5.36; 0.08) | 4.24 | 0.056 |
| Free fat mass, % | 76.542 ± 9.052 | 79.33 ± 0.16 | 81.469 ± 7.356 | 79.36 ± 0.19 | 0.03 (-0.52; 0.57) | 0.01 | 0.922 |
| Fat mass, % | 23.458 ± 9.052 | 20.32 ± 0.50 | 18.531 ± 7.356 | 18.66 ± 0.58 | -1.66 (-3.35; 0.03) | 4.30 | 0.054 |
| Handgrip strength (right), kg | 47.80 ± 13.935 | 48.94 ± 0.80 | 48.92 ± 13.543 | 47.49 ± 0.93 | -1.45 (-4.17; 1.27) | 1.28 | 0.274 |
| Resting energy exp., kcal | 1401.50 ± 440.661 | 1616.38 ± 79.46 | 1475.08 ± 264.723 | 1483.31 ± 92.0 | -133.07 (-405.22; 139.08) | 1.07 | 0.315 |
aβ = mean difference between treatments over the time, adjusting the covariate: sex and % body fat, % free fat mass, % gynoid fat and fat mass in grams.
bPost analysis data were estimated for covariate (sex and % body fat, % free fat mass, % gynoid fat and fat mass in grams.)
cIn bold: P < 0.05.
4. Discussion
This study shows that 8-weeks of high power training CrossFit program, based on progressive resistance, power strength and functional training, improved resting energy expenditure, and all body composition parameters. It’s particularly more effective in total fat mass losses compared to high intermittent swimming training.
No differences were found in changes on arms and legs free fat mass between the two groups, but in a medium long time, CrossFit seems to have important effects on legs free fat mass. This potential of CrossFit, specifically in legs improvement, has been described previously in a study performed by Glassman in 2006 (10). Our data showed that CrossFit also increased muscle strength. But no significant differences between trainings were found. Thus, regarding the REE data, the CrossFit was no more effective than swimming in increasing this parameter. This last data might explain the association with the decrease in total fat mass and the increasing in free fat mass. This relationship has been reported in several studies on the general population (11, 12).
Limitations included the small size of the sample and a previous history of moderate training for all participants. Finally, because of the small sample size, these results may not generalize outside of these participants. This study included a control condition but no randomization were made.
Study strengths included adherence: drop-out rates of 13 % (2/15) for swimmer and 33% (5/15) for crossfitter participants. Only one crossfitter subject experienced a serious injury (these episodes are typical in CrossFit as described in literature (13).
The CrossFit training was safely conducted among participants of our study. Another point of strength was the assessment of body composition using DXA, which is the gold standard for body composition evaluation.
Future research could include a larger sample with extended follow-up to determine the effects of CrossFit high intensity power during a medium long time period.
4.1. Conclusions
Overall, both forms of training appear to have caused the same improvements in the body composition of all athletes, but between thegroups, the crossfitter group have seen more effects on fat mass decrease, specifically in the reduction of gynoid and android fat. Future approaches of CrossFit training: it could also be administered in conjunction with nutrition intervention in the hope of eliciting changes to body composition in a large samples of overweight or obese participants.
