Sales of laptop computers passed desktops in the U.S. for the first time ever this fall, according to market-research firm IDC.

That's bad news for backs, necks and shoulders.

'Laptops are inherently unergonomic -- unless you're 2 feet tall,' says physician Norman J. Marcus, a muscle-pain specialist in New York City.

When you work at a computer, the keyboard should be at elbow height, so your upper and lower arms form an angle of 90 degrees or more and your forearms are supported by armrests. The monitor should be roughly at eye level so you can lean back in a chair with back support.

But most users simply set their laptops on a desk or table. The keyboard is too high, which makes your arms reach up, your shoulders hunch and your wrists bend down. The monitor is too low, which pulls your head and neck forward and down and puts a strain on your back.

That's OK if you use your laptop occasionally, for short periods. But if you use one for hours at a stretch -- as do millions of college students, business travelers, telecommuters, video-gamers and growing numbers of office workers -- you're setting yourself up for muscle problems that can make your entire upper body hurt.

Ergonomics experts have warned about laptop problems for years -- mostly in vain. People continue to abandon bulky desktops in favor of the ever-sleeker, lighter portables. And WiFi connections let us use laptops anywhere -- in bed, on the floor -- in all kinds of contorted positions.

'People think, 'How can a mouse or a keyboard hurt you?'' says Thomas Caffrey, founder of Myofactors LLC, which does ergonomic consultations for factories and offices (including The Wall Street Journal). 'But poor technique can significantly overload the anatomy over time.'

A wrong position can cause pain and stiffness in the neck, shoulders, back and arms, as well as headaches, pains in the temporomandibular joint (TMJ) and carpal tunnel syndrome, in which pressure on wrist nerves causes tingling and numbness in the hands.

There are simple ways to make a laptop more ergonomic. The key is to separate the keyboard and the monitor so each can be placed at the proper height:

-- Laptop stands. Getting the monitor higher is simple -- setting it on a pile of books will do. Or you can buy stands ($20 and up) that hold your laptop vertically; some let you adjust the height and angle. Either way, you'll need a separate keyboard so your hands aren't at an impossible angle.

External keyboards. These sell for as little as $20; wireless versions for $60 and up. Logitech makes a wireless-keyboard-and-laptop-stand set for $80. A keyboard that slopes away from you provides the best angle for your hands and wrists.

-- Keyboard tray. Unless you're really tall, setting the keyboard at elbow level means a few inches below desk height. Attachable keyboard drawers range from $30 to $200. If your desk isn't wide or deep enough, try setting the keyboard on your lap with a small cushion under the front edge. (Don't use a laptop on your unprotected lap for long; they can get hot .)

-- External mouse. If you find the built-in mouse awkward, get an external mouse or keypad ($14 to $75) and set it close to the keyboard. 'The farther your hand has to go from your body, the more burden there is on the upper extremities,' says Mr. Caffrey.

-- Docking stations. These allow you to attach a separate monitor, keyboard and mouse and use your laptop as a central processing unit (CPU). Prices start around $70. This is a good solution for workers who need a laptop for traveling as well as long periods of office work.

-- Portable solutions. Lapdesks and mini-stands ($4 to $50) make laptops more ergonomic on the go. They raise the monitor slightly by elevating the back edge of the computer. Tamara James, ergonomics director at Duke University, tells students who bring laptops to class that setting them on a two- or three-inch binder will have the same effect. Mr. Caffrey worries that mini-stands may be hard on wrists and hands and suggests reversing the angle to elevate the keyboard instead. Try alternating between the two positions if you're on the laptop a lot.

'Don't just put your laptop on your desk -- that's probably the worst place for it,' says Ms. James, who says people are usually amenable to such suggestions once muscle strain sets in. 'Pain is a pretty good motivator,' she says.

據(jù)市場研究公司國際數(shù)據(jù)公司(IDC)的數(shù)據(jù)，今年秋季美國筆記本電腦銷量有史以來首次超過臺式電腦銷量。

但對人的頸、肩、背來說，這是個壞消息。

紐約市肌肉疼痛科醫(yī)生諾爾曼•馬庫斯(Norman J. Marcus)說，筆記本電腦本質(zhì)上是不符合人體工程學的，除非你身高只有兩英尺。

當你在電腦前工作時，鍵盤應該和肘部齊高，這樣你的大臂與小臂成90度角或更大的角度，小臂可以放在椅子扶手上。顯示器應該大概和眼睛處于同一水平線，這樣你就能往后靠在椅背上。

但是，大部分使用者都只是把筆記本電腦放在書桌或是普通桌子上。鍵盤放得太高，你必須把胳膊伸得老高，聳起肩膀彎著手腕。顯示器太低，你的腦袋和脖子都必須往前下方伸，使你的背部緊張。

如果你只是偶爾、短時間地用一下筆記本電腦，這樣做不會有太大問題。但是，如果你一坐就是幾個鐘頭（就像好幾百萬大學生、商務旅客、網(wǎng)絡上班族、游戲玩家，以及越來越多的辦公室白領一樣），那你就是在和自己的肌肉過不去，這可能會讓你的整個上身疼痛。

人體工學專家多年來一直在提醒筆記本電腦的問題，但是往往是徒勞無功。人們繼續(xù)丟掉笨重的臺式電腦，轉(zhuǎn)向更加輕薄的筆記本電腦。而且無線上網(wǎng)技術還讓我們可以在任何地方使用筆記本電腦──床上、地板上──姿勢也可以千奇百怪。

Myofactors LLC的創(chuàng)始人托馬斯•凱弗雷(Thomas Caffrey)說，人們會想，一個鼠標或鍵盤怎么會使你受到傷害呢？但是隨著時間的推移，糟糕的姿勢可能會對人體帶來明顯的重負。該公司為工廠和辦公室（包括《華爾街日報》）提供人體工學咨詢服務。

錯誤的姿勢不但可以造成頸、肩、背和手臂的疼痛和僵硬，而且還會導致頭痛、顳下頜關節(jié)疼痛和腕管綜合癥。腕管綜合癥患者的腕部神經(jīng)受到壓迫，導致手上產(chǎn)生刺痛或是麻木的感覺。

有幾種簡單的方法可以讓使用筆記本電腦更符合人體工學。關鍵是要將鍵盤和顯示器分開，這樣兩者可以分別放在合適的高度。

－筆記本電腦支架。把顯示器放高很容易──把它放在一摞書上就可以了。你也可以買個支架（最低20美元），把你的筆記本電腦垂直放置，有些支架還可以調(diào)整高度和角度。無論哪種方法，你都需要一個單獨的鍵盤，這樣你的手才不必彎成一個高難度的角度。

－外接鍵盤。最低只要20美元，無線鍵盤至少60美元。Logitech生產(chǎn)的一種無線鍵盤加筆記本支架的套裝價格是80美元。如果鍵盤能朝遠離你的方向傾斜一個角度，你的手、腕就可以處于最佳角度。

－鍵盤托架。除非你是個小巨人，否則把鍵盤放在肘部的高度也就是只比書桌低幾英寸�？筛芥I盤托架價格從30美元到200美元不等。如果你的書桌不夠長也不夠?qū)�，那么試著把鍵盤放在你的腿上，在前緣下面放一個小墊子。（不要把筆記本電腦單放在腿上太長時間，電腦會很燙的。）

－外接鼠標。如果你覺得內(nèi)置的鼠標不舒服，那么就配一個外接鼠標或是袖珍鍵盤（14-75美元），把它放在鍵盤旁邊。凱弗雷說，你的手伸的越遠，承受的負擔越重。

－擴展塢。它讓你可以外接顯示器、鍵盤和鼠標，把你的筆記本電腦當成一個中央處理器。起價約為70美元。對于那些需要在辦公室中長時間使用筆記本電腦，同時也需要在旅途中使用的人來說，這是個很好的解決方案。

－便攜解決方案。電腦桌和迷你支架（4-50美元）讓筆記本電腦在使用中更加符合人體工學。它們抬高了電腦的后緣，進而略微升高了顯示器。杜克大學人體工學主任塔馬拉•詹姆斯(Tamara James)告訴那些把筆記本電腦帶到課堂上的學生們說，把電腦放在一個兩、三英寸高的活頁夾上也會達到同樣的效果。凱弗雷擔心迷你支架可能會使得腕和手緊張，他建議反過來把鍵盤抬高。如果你經(jīng)常使用筆記本電腦，那么就試著輪換使用這兩種姿勢。

詹姆斯說，不要只是把筆記本電腦放在書桌上，書桌或許是放筆記本電腦最糟糕的地方。她說，人們一旦出現(xiàn)肌肉緊張的癥狀，就會非常愿意接受她的建議。她說，疼痛是種不錯的動力。