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The utility of accelerometers to predict stroke rate in captive fur seals and sea lions

机译:加速度计在圈养海狗和海狮中预测冲程率的实用程序

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The energy expenditure of free-living fur seals and sea lions is difficult to measure directly, but may be indirectly derived from flipper stroke rate. We filmed 10 captive otariids swimming with accelerometers either attached to a harness (Daily Diary: sampling frequency 32?Hz,?N=4) or taped to the fur (G6a+: 25?Hz,?N=6). We used down sampling to derive four recording rates from each accelerometer (Daily Diary: 32, 16, 8, 4?Hz; G6a+: 25, 20, 10, 5?Hz). For each of these sampling frequencies, we derived 20 combinations of two parameters (RMW, the window size used to calculate the running mean; and?m, the minimum number of points smaller than a local maxima used to detect a peak) from the dynamic acceleration of x, z and x+z, to estimate stroke rate from the accelerometers. These estimates differed by up to ~20% in comparison to the actual number of foreflipper strokes counted from videos. RMW and the choice of axis used to make the calculations (x, z or x+z) had little effect on the overall differences, though the variability was reduced when using x+z. The best?m?varied depending on the axis used and the sampling frequency; a larger?m?was needed for higher sampling frequencies. This study demonstrates that when parameters are appropriately tuned, accelerometers are a simple yet valid tool for estimating the stroke rates of swimming otariids.
机译:自由活动的海狗和海狮的能量消耗很难直接测量,但是可能间接地从鳍状肢的冲程率中得出。我们拍摄了10只圈养的otariids,它们的加速度计要么系在安全带上(每日日记:采样频率32?Hz,?N = 4),要么贴在皮毛上(G6a +:25?Hz,?N = 6)。我们使用下采样从每个加速度计得出四个记录速率(每日日记:32、16、8、4?Hz; G6a +:25、20、10、5?Hz)。对于这些采样频率中的每一个,我们从动态推导两个参数的20种组合(RMW,用于计算运行平均值的窗口大小;μm,小于用于检测峰值的局部最大值的最小点数) x,z和x + z的加速度,以从加速度计估算冲程速率。与从视频中算出的前肢笔触的实际数量相比,这些估计值相差高达〜20%。 RMW和用于进行计算的轴的选择(x,z或x + z)对总体差异的影响很小,尽管使用x + z可以降低可变性。最佳值取决于所使用的轴和采样频率。更高的采样频率需要更大的μm。这项研究表明,对参数进行适当调整后,加速度计是一种简单但有效的工具,可用于评估游泳otariids的冲程率。

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