長時間の立ち仕事は健康に大きな被害をもたらす

●1日5時間立っていると慢性的で強い下肢筋肉の疲労につながり、運動制御・（特に腰部-股関節の）姿勢制御を変容させることで長期的な腰痛・筋骨格障害のリスクが高まる可能性があるという。

●2時間以上の立位での作業は腰痛のリスクを増やす（Waters and Dick, 2014）が、ヨーロッパ労働条件調査によると、労働者の47%は1日の時間の75%以上を立って過ごしている。

●製造工場のシフトを再現し、対象者全員に軽作業をシミュレートしてもらった。作業台で5時間立ち、複数回の5分間の休憩と30分の昼食休憩を設けた。

●姿勢の重心動揺と脚筋の応力をモニターし、 対象者に不快感を報告してもらったところ、年齢・性別にかかわらず、作業日の終了時に著しい疲労を感じていた。

●5時間の立ち作業終了後30分以上にわたり、筋疲労の明らかな徴候がみられた。またこの疲労に自覚がない可能性も示唆された。

●研究者は「定期的なストレッチ運動や決まった休憩、仕事のローテーション、より動的な動作を取り入れることで、慢性疲労の影響は軽減される可能性がある」と示唆している。

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Long-Term Muscle Fatigue After Standing Work

Hum Factors. 2015 Jun 5[Epub ahead of print] doi:**********

Abstract

Objective The aims of this study were to determine long-term fatigue effects in the lower limbs associated with standing work and to estimate possible age and gender influences. Background The progressive accumulation of muscle fatigue effects is assumed to lead to musculoskeletal disorders, as fatigue generated by sustained low-level exertions exhibits long-lasting effects. However, these effects have received little attention in the lower limbs. Method Fourteen men and 12 women from two different age groups simulated standing work for 5 hr including 5-min seated rest breaks and a 30-min lunch. The younger group was also tested in a control day. Muscle fatigue was quantified by electrically induced muscle twitches (muscle twitch force [MTF]), postural stability, and subjective evaluation of discomfort. Results MTF showed a significant fatigue effect after standing work that persisted beyond 30 min after the end of the workday. MTF was not affected on the control day. The center of pressure displacement speed increased significantly over time after standing work but was also affected on the control day. Subjective evaluations of discomfort indicated a significant increase in perception of fatigue immediately after the end of standing work; however, this perception did not persist 30 min after. Age and gender did not influence fatigue. Conclusions Objective measures show the long-term effects of muscle fatigue after 5 hr of standing work; however, this fatigue is no longer perceived after 30 min of rest postwork. Application The present results suggest that occupational activities requiring prolonged standing are likely to contribute to lower-extremity and/or back disorders.

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