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This is an open access article under the terms of the Creat ive Commo ns Attri bution-NonCo mmercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Aging of the population has increased due to the decline in fertility rate and increase in life expectancy in Japan. In 2006, the labor force participation rate of older workers aged 60 and older was reached to 30.2% 1) . Memory functions such as storing and retrieving recent information from memory correctly are very important in our daily lives and work. They allow or guide us to make a decisions or form responses in a proper way in ever-changing environments. A decline in visual memory, especially in the manufacturing industry, would be very critical to workers, as the workplace requires them to process lots of visual information with considerable speed. Additionally, it is suggested that the memory performance in older people is lower compared with that of young people when faced with new and/or complex information 2) . One of the methods of evaluating the memory performance is the recognition memory test 3) . In this test, a participant is asked to remember a set of items for a certain period of time; this is referred to as the encoding phase. Later, the same items as those presented in the encoding phase (old items) and a new set of items are shown to the participant in a random order. The participants are asked to indicate if each item is an old (yes) or a new (no) item by retrieving the information from their stored memories (test phase). The researcher then calculates the hit rate (yes response to the old item) and false alarm rate (yes response to the new item) and also estimates the individual's discrimination ability (ability to discriminate between old and new items) and response bias scores (a decision criterion to apply when responding to the items) 3) . Researchers have used this method to evaluate the memory performance of different groups of participants under various conditions.As we age, our visual memory declines; it is The conditions consisted of combinations of encoding times of two and four seconds (E2 and E4) and first and second retrieval practice test trials (T1 and T2): E2T1, E2T2, E4T1 and E4T2. Performance was evaluated by measuring hit rates, false alarm rates, discrimination ability and response bias. Results: Older adults showed better improvement of hit rate and discrimination ability under the E4T2 conditions whereas young adults showed better memory performance under the E2T2 conditions. Conclusions: A longer encoding time and repetition of the test was effective in improving the visual memory performance in terms of the hit rates and discrimination ability of older adults. The results suggest that this strategy should be useful in providing a suitable work environment for older workers. (J Occup Health 2014; 56: 453-460)

In the workplace, localized muscle fatigue can be a limiting factor for prolonged static work. It is important to study the etiology of fatigue in the muscle to prevent discomfort and potential muscle injury. The purpose of this study was to investigate the effect of sustained trunk flexion and loading on the erector spinae muscles (ESM) fatigue using electromyography (EMG) and muscle oxygenation (Mox) changes. Twelve healthy male volunteers, aged between 19 and 28 years (mean age 23 +/- 2.6), participated in this study. The subjects held a load (5, 10 and 15 kg) and no load in their hands whilst sustaining trunk flexion at 60 degrees and also in an upright standing posture for 30 seconds. Five minutes rest was given between the conditions, and each condition was randomly repeated three times. Surface EMG and near-infrared spectroscopy were recorded. Root mean square and median frequency (MF) of EMG, and Mox were calculated. The results showed a greater decrease in Mox with an increase in loads over time (P = 0.015). Using unloaded trunk flexion as a control to ascertain load effect resulted in a significant difference in Mox in the unloaded condition and in the 15 kg condition (P = 0.027). EMG results showed a significant decrease in the MF over time in trunk flexion while holding a load (P < 0.001). These results show objectively that trunk flexion while holding loads causes ESM fatigue.