Nike is facing one of its most challenging periods in decades

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• Nike shares slumped after the company said sales would fall. The stock is down 30% this year.
• The sportswear brand has started implementing a turnaround plan, but the results are yet to be seen.
• Nike's reliance on its lifestyle business seems to be hurting it, one analyst said.

Nike's lost its stride — and is finding it hard to get its pace back up.

In December, the company announced...