496


EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2017


TABLE 2: Mean and standard deviation (s.d.) for cross-sectional area (CSA) of m. multifidus muscle at four spinal levels at Days 0, 30 and 60 of whole body vibration treatment


Day 0 CSA (n = 9)


Spinal region T15–16


T16–17 T18–L1 L1–2


Day 30 CSA (n = 9)


Day 60 CSA (n = 8)


Mean s.d. Mean s.d. Mean s.d. 8.431* 0.678 8.782* 0.471 9.243* 0.713


9.111† 8.539‡ 8.162§


0.673 9.387† 0.771 8.953‡ 1.289 8.456§


0.527 9.956† 0.717 9.471‡ 1.167 8.812§


0.693 0.829 1.511


T, thoracic vertebra; L, lumbar vertebra; CSA, cross-sectional area in cm2. *,†,‡,§All values are statistically significantly different (P<0.01).


CSA of the m. multifidus increased and this is biologically relevant (Table 2).


M. multifidus CSA symmetry with WBV For all analyses of m. multifidus CSA symmetry, data were grouped by participant. The grouping provided four values (T15–T16, T16–T17, T18–L1 and L1–L2) for each participant (n = 9); thus 36 paired values for analysis (n = 36). The n is provided for each analysis and those that are different than 36 are the result of missing data. The data are three repeated measures (Days 0, 30 and


60) and not normally distributed; thus a Freidman test with listwise exclusion was performed to determine if there were differences in mean ranks (means) of the symmetry score of the m. multifidus CSA at Days 0, 30 and 60 of WBV. A


statistical difference was found (X2 (2, n = 24) = 6.083, P = 0.05). This indicates that there was a difference among the three mean ranks (means) for Days 0, 30 and 60. The three orthogonal contrasts were performed using a Wilcoxon signed rank test with listwise exclusion. To hold the experiment-wise type 1 error to less than 0.05, Bonferroni correction (comparison-wise alpha = 0.013) was used. The


contrast between Days 0 and 60 (n = 24, z = 2.657, (P<0.01, r = 0.54)) s found to be statistically significant, whereas contrast between Days 0 and 30 and Days 30 and 60 was


not statistically significant. The r effect size is greater than the absolute value of 0.54 and this is considered larger than typical in many other fields (Cohen 1988; Nakagawa and Cuthill 2007); thus the authors feel this is a clinically relevant improvement in left to right symmetry of the m. multifidus CSA. The statistically significant contrast indicates that as the duration of WBV increased the symmetry score in the CSA of


TABLE 3: Mean, minimum, maximum and standard deviation (s.d.) of symmetry score for cross-sectional area (CSA) of m. multifidus muscle at Days 0, 30 and 60 of whole body vibration treatment


Symmetry score (n = 9)


Days of treatment Day 0


Day 30 Day 60


Minimum Maximum Mean s.d. 0.41


0.28 0.15


26.29 19.79 22.36


6.39* 5.26


4.25* *All values are statistically significantly different (P<0.01). © 2016 EVJ Ltd


7.81 6.21 6.39


the m. multifidus decreases, meaning that the CSA of the m. multifidus from left and right became more symmetrical and this is biologically relevant (Table 3).


Discussion


This study shows that WBV is capable of increasing the total (left and right) CSA at each spinal level in the horse (Table 2, Figs 3 and 4), an indicator of m. multifidus hypertrophy. Furthermore, an improvement in m. multifidus symmetry takes place over the 60 days of WBV, seen by the CSA symmetry ratio moving towards zero (Table 3). The ability of WBV to increase CSA of the paraspinal musculature (Gilsanz et al. 2006), as well as minimise m. multifidus


deconditioning (Belav


described in man, but to the best of the authors’ knowledge, has never been investigated in the horse. No significant change in m. multifidus CSA was seen over time without WBV treatment, indicating that the horse’s current environment, diet and exercise programme had no significant impact on the m. multifidus size over time. In contrast, addition of WBV to each horse individual exercise programme was able to induce hypertrophy of the m. multifidus in as early as 30 days and m. multifidus hypertrophy continued during the second 30 days of WBV. The muscle response to training will depend on the


primary function of the muscle and whether or not the training stimulus is appropriate for that particular muscle function and composition. In horses, the m. multifidus is comprised of approximately equal muscle fibre type (MFT–I) (slow twitch) and MFT-II (fast twitch) fibres indicating a dual postural and locomotor role (Hyyti€


ainen et al. 2014). The


functional anatomy of the m. multifidus is comparable to that in man comprising a series of overlapping fascicles running caudo-laterally, spanning one to five intervertebral joints. There are superficial and deep fascicles with the superficial fascicles being longer (Stubbs et al. 2006). In man, it appears that dynamic static resistance training


(an exercise combining movement with a static holding pattern) is most effective in increasing CSA of the multifidus muscle (Danneels et al. 2001). This can be explained by the recruitment of a larger number of motor units, including both the low threshold motor units (MFT-I) and high threshold motor units (MFT-II) (Goldspink and Harridge 2002). In horses, the same principle regarding motor unit recruitment is true. It is, a larger number of motor units will be recruited as intensity, duration and speed of exercise increases (Rivero and Piercy 2008).


Horses standing quietly on a WBV platform perform, strictly


speaking, a static rather than a dynamic static exercise such as dynamic mobilisation exercises described by Stubbs et al. (2011). However, WBV on itself appears to be similar to a dynamic static exercise. This seems to be confirmed by at least one research paper, showing that WBV training was superior to a low intensity resistance training in improving static and dynamic muscle strength in man (Verschueren et al. 2004). This idea is further supported by research findings in mice and rats using similar type WBV platforms as used in this study that show that WBV is able to induce both changes in MFT-I and MFT-II fibres (Xie et al. 2008; Lochy


nski et al.


2013), indicative for high muscle activation as seen with dynamic static exercises and resistance training. This high


atrophy during bed rest induced y et al. 2008) has previously been


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