The fatty organ is the single largest buoyancy providing structure in the coelacanth body and in the studied specimen constitutes 0.74% of the total volume of the specimen at surface pressure and room temperature. Mapping lipid fraction using Dixon MRI revealed an uneven distribution of lipids in the fatty organ which can be observed by visualizing a medium sagittal section of the organ (Fig. 5a, notice higher lipid fraction in posterior portion of the fatty organ), and by plotting net buoyancy over the length of the organ (Fig. 5b). This observation was supported by magnetic resonance spectroscopy that revealed a more pronounced methylene group signal in the posterior portion of the fatty organ, and reversely a more pronounced water signal in the anterior portion (Fig. 5c).
Predictions of buoyancy and hydrostatic balance rely on precise measurements of the distribution of lipid, lean tissue, and mineralized tissue. Overall, our non-invasive observations on the distribution of lipid-rich tissues in the coelacanth are in agreement with previous destructive measurements [33,34,35]. However, because it constitutes a large quantity of the body mass and thus is of importance in the overall measurement of absolute buoyancy, it should be noted that we observed a smaller lipid fraction of ventral but not dorsal muscle than has previously been reported (ventral muscle 12.77% (present study) vs. 34.1% , dorsal muscle 10.15% (present) vs. 7.7% . All percentages in wet weight). In addition, our chemical extraction of lipids in a ventral muscle sample also yielded a lipid fraction more similar to our non-invasive measurements than literature values (4.34% of wet weight) and magnetic resonance spectroscopy supported a low level of lipids in muscular tissue (Additional file 4). This discrepancy between present and literature data on the fattiness of muscle tissue may be ascribed to large muscle samples containing lipid-rich intermuscular fat (68.13% lipid, see Table 1) being analyzed in previous destructive examinations. Although muscle sample size was not reported by Nevenzel and colleagues , they described that a similar protocol was used as they previously applied on Ruvettus pretiosus using a 276-g portion of flesh . Such a large muscle sample most likely contained intermuscular fat, and the discrepancy in lipid fraction of ventral and dorsal musculature found by Nevenzel and colleagues  but not in the present study, could be caused by a difference in distribution of intermuscular lipid rather than an actual difference in true muscular lipid fraction (see Additional file 8). In this way, three-dimensional imaging provides an increased spatial resolution of the distribution of different tissue components. To refine the buoyancy modeling method presented in this study even further, it would be of interest to separate tissue components into more than the three dominant density classes used here: lipid, lean tissue, and bone mineral. In elasmobranchs, the balancing osmolytes urea and trimethylamine oxide also provide buoyancy . Since these components are also found in high concentration in coelacanth fluids especially in the large notochordal canal [56, 57], the ability to map these chemicals using, e.g., more sensitive magnetic resonance spectroscopy or other non-invasive techniques would provide an additional refinement of buoyancy modeling. We did not observe solidification of the dominant wax ester oleyl oleate at the relevant temperatures used in this study; however, it would also be of interest to investigate this for the mix of wax esters found in coelacanth lipid deposits , since phase shift can cause rapid density shifts and thus alter overall buoyancy as suggested in cetaceans [38, 39].
Acquired CT and MRI data in 16-bit color depth was initially reformatted into 32 bit for precision of subsequent calculations. Thereafter, CT data outputted in Hounsfield units was converted into bone mineral density using the calibration phantom and lipid- and water-specific images of the MRI data were converted into lipid and water fraction images. Quantitative CT data was then adjusted for the effect of ethanol preservation on measurements of bone mineral content, and MRI data was adjusted for the effect of ethanol preservation on measurements of lipid content. Both datasets were cropped in each dimension to only include specimen voxels and background pixels were removed using the ImageJ Threshold plugin. Both the CT and the MRI datasets were segmented into 35 segments: main body, fatty organ, left/right pectoral fins, left/right pelvic fins, 1st and 2nd dorsal fins, anal fin, and 26 sequential caudal segments. For each segment, average proportions of bone mineral, lipid, and water (lean tissue) was measured in every slice in the transversal, sagittal, and coronal plane, respectively, using the ImageJ multi-measure function. While both CT and MRI datasets where isotropic and covered the entire coelacanth specimen, image resolution was 357.9 times higher in the CT dataset (0.2 mm vs. 1.42 mm in each spatial dimension), thus resulting in 7.1 times the number of slices spanning the specimen in each spatial dimension. To allow for the combination of bone mineral content measurement from CT with lipid and water content from MRI, each slice measurement of bone mineral content was scaled by the number of slices in the same spatial dimension of the MRI dataset and then binned by the number of slices in the CT dataset, thus resulting in slice measurements in equal numbers.
Symmetry during lifting is considered critical for allowing balanced power production and avoidance of injury. This investigation assessed the influence of elevating the heels on bilateral lower limb symmetry during loaded (50% of body weight) high-bar back squats.
This novel investigation adds to the body of knowledge in this field by using contemporary analytical procedures to assess the influence of elevating the heels on lower limb symmetry during the high bar squat. The key findings highlight that although a degree of bilateral lower limb asymmetry is common in individuals performing back squats, the degree of this symmetry is largely unaffected by raising the heels. Our results also show that when using traditional discrete measures of bilateral symmetry, the regular weight training group presented with more asymmetry than the novices, while analyses of time-series data indicated asymmetries in the novice group only. This project also emphasizes the limitations of traditional measures of bilateral symmetry and highlights advantages of quantifying symmetry in time-series data using SPM1D. 2b1af7f3a8