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背要直，只弯两膝。
Keep back straight and bend knees.
youdao
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因为双膝一直僵直，那么整个重量势必都将由下背部的肌肉负担。
Because both knees are always tetanic, lower back's muscle will burden all weight.
youdao
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因为双膝一直僵直，那么整个重量势必都将由下背部的肌肉负担。
Because both knees are always tetanic, lower back's muscle will burden all weight.
youdao