A mini-workout may help memory as much as a nap after sleep loss

Going without sleep makes it harder to concentrate and learn new information. And for people who work overnight or face an occasional period of severe sleep loss, getting enough rest may not always be possible in the moment.

Can anything help us focus besides sleep? A recent study published in the scientific journal Proceedings of the National Academy of Sciences compared two strategies for protecting memory after sleep deprivation: aerobic exercise and a nap. Researchers wanted to know whether a short bout of exercise really provides some of the same cognitive benefit as a nap. As it turns out, the answer may be yes.

So, what does this finding mean for everyday sleep and exercise habits?

To help understand how people can apply these results, I spoke with CNN wellness expert Dr. Leana Wen. Wen is an emergency physician and clinical associate professor at George Washington University. She previously was Baltimore’s health commissioner.

CNN: How did researchers go about identifying the effect of exercise versus napping?

Dr. Leana Wen: The study enrolled a small number of healthy adults ages 18 to 35 and kept them awake for 30 hours. The 54 participants were then randomly assigned to one of three groups. One performed 20 minutes of moderate-to-vigorous cycling, at 80% of their maximum heart rate. Another had a 90-minute opportunity to nap. The control group sat on a stationary bicycle for 20 minutes without exercising.

Afterward, participants viewed 150 images while researchers recorded their brain activity using electroencephalography, or EEG. They did not know there would subsequently be a memory test. Three days later, after having time to recover from the sleep deprivation, they were shown the original images mixed with new ones and asked which they remembered.

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Participants who exercised correctly recognized 56% of the images, compared with 57% among those who napped and 46% in the control group. Both the exercise and nap groups performed significantly better than the control group, with memory performance about 21% higher after exercise and 23% higher after a nap. There was no significant difference in benefit between exercise and napping.

Interestingly, participants who napped reported feeling significantly less fatigued afterward, while those who exercised reported similar levels of fatigue as the control group. Despite feeling just as tired, the exercise group performed significantly better on the memory test than the control group.

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CNN: How could 20 minutes of exercise help memory after someone has been awake for so long?

Wen: Sleep deprivation interferes with the brain’s ability to encode new information. After prolonged wakefulness, sleep pressure builds and the neural processes needed to form memories become less efficient.

The EEG recordings suggest that exercise helped counteract some of these effects. It reduced a marker of neural fatigue in brain regions involved in the memory task. One possible hypothesis is that exercise helps the sleep-deprived brain use its available cognitive resources more efficiently.

The 20-minute workout also fits into a broader concept known as exercise “snacking,” though it was longer than most exercise snacks. These are short bursts of physical activity typically lasting anywhere from about 30 seconds to five or 10 minutes. Activities can include climbing stairs, brisk walking, doing squats or other activities that raise the heart rate. Studies have suggested that these small doses of movements have health benefits, such as improving cardiorespiratory fitness and even reducing the risks of cancer and dementia.

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CNN: Did exercise and napping help the brain in the same way?

Wen: Not exactly, and in my view, this was one of the most interesting findings. Exercise and napping produced similar memory performance benefits, but through different neural processes.

The nap changed the underlying state of the sleep-deprived brain. People in the nap group had less fatigue and lower EEG markers of sleep pressure, which is the biological drive for sleep that builds the longer someone stays awake. Measures related to this improved brain state were strongly associated with how well participants formed new memories.

Exercise did not relieve sleep pressure in the same way. Instead, it appeared to make memory processing more efficient. We can think of the distinction in this way: The nap gave the brain some of the sleep it was demanding, while exercise helped the brain function more effectively despite still being sleep-deprived.

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CNN: Can someone who is sleep-deprived exercise instead of taking a nap?

Wen: No. Exercise cannot replace sleep. Sleep serves essential functions throughout the body, including regulating immune and metabolic processes and supporting many aspects of brain function. A 20-minute workout cannot provide those functions, although regular exercise does help sleep and vice versa.

The study asked a much narrower question: If someone has already experienced severe sleep loss, can an intervention protect one particular cognitive ability, the formation of new memories? For that outcome, in the specific circumstances of this study, 20 minutes of exercise and a 90-minute nap produced comparable results.

There are situations where this could have practical applications. Healthcare workers, transportation workers and others in safety-sensitive occupations can experience unavoidable sleep loss, and there may not always be time or an appropriate place for a 90-minute nap. A short bout of exercise could offer another strategy for preserving memory. But someone should not interpret these results to mean that exercise makes it safe to drive or perform other dangerous tasks while severely sleep-deprived.

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CNN: Can we apply these findings to people tired from a bad night of sleep or who routinely do not get enough sleep?

Wen: We should be specific about clarifying what was tested. This was a small laboratory study of young, healthy adults who had been continuously awake in laboratory conditions for 30 hours. The researchers tested one particular exercise regimen and one aspect of cognition.

We don’t know whether the same benefit occurs after chronic sleep restriction, in older adults with medical conditions, or with other types or intensities of exercise. Nor did the study show that exercise restores attention, reaction time, judgment or the many other functions impaired by sleep deprivation. Those are questions for larger studies in real-world settings, particularly among shift workers and others who regularly experience sleep loss.

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CNN: What should people do if they are sleep-deprived but need to function well that day?

Wen: The first priority is to try and get sleep. Adults should aim to get at least seven hours of sleep on a regular basis. A nap can be useful when adequate nighttime sleep has not been possible. If a nap is not possible, a short bout of aerobic exercise could be useful before a period that requires learning and memory. Someone could take a brisk walk , climb stairs or use a stationary bike.

Caffeine can temporarily increase alertness and concentration and maybe even reduce dementia risk long term, though it does not reverse the effects of sleep deprivation. People should also eat regular, balanced meals and stay hydrated. Large, heavy meals can increase sleepiness, and alcohol should be avoided because it can further impair alertness and judgment.

People also need to recognize the limits of these strategies and recognize that they do not make it safe to drive or perform other potentially dangerous tasks when severely sleep-deprived.

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睡眠不足会降低注意力集中度和学习新知识的能力。对于上夜班或偶尔会严重睡眠不足的人来说，有时可能无法立即获得充足的休息。

除了睡眠之外，还有什么方法能帮助我们集中注意力吗？最近发表在《美国国家科学院院刊》（PNAS）上的一项研究比较了两种在睡眠不足后保护记忆力的方法：有氧运动和午睡。研究人员想知道，短暂的运动是否真的能像午睡一样带来认知益处。结果表明，答案可能是肯定的。

那么，这一发现对日常睡眠和运动习惯意味着什么呢？

为了帮助人们了解如何应用这些研究结果，我采访了CNN健康专家莉娜·温博士。温博士是乔治·华盛顿大学的急诊医生和临床副教授，此前曾担任巴尔的摩市卫生局局长。

CNN：研究人员是如何确定运动与午睡的效果的？

莉娜·温博士：这项研究招募了少量年龄在18至35岁之间的健康成年人，并让他们保持清醒30小时。随后，54名参与者被随机分配到三个组。一组进行了20分钟的中高强度自行车骑行，心率达到最大心率的80%。另一组有90分钟的午睡时间。对照组则在固定自行车上静坐20分钟，不进行任何运动。

随后，参与者观看了150张图片，研究人员使用脑电图（EEG）记录了他们的脑部活动。他们并不知道之后会进行记忆测试。三天后，在睡眠不足的情况下，他们恢复过来，研究人员向他们展示了最初的图片和一些新图片，并询问他们记得哪些图片。

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锻炼组的参与者正确识别了56%的图片，而午睡组的正确率为57%，对照组为46%。锻炼组和午睡组的表现均显著优于对照组，锻炼后记忆力提高约21%，午睡后提高约23%。锻炼和午睡在提升记忆力方面并无显著差异。

有趣的是，午睡的参与者表示午睡后疲劳感明显减轻，而运动的参与者则表示疲劳程度与对照组相似。尽管感觉同样疲惫，运动组在记忆力测试中的表现却明显优于对照组。

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如果忧虑让你难以入睡，专家知道该如何应对。

CNN：一个人长时间清醒后，20分钟的运动怎么能帮助提高记忆力呢？

温：睡眠不足会干扰大脑编码新信息的能力。长时间清醒后，睡眠压力会积聚，形成记忆所需的神经过程效率会降低。

脑电图记录表明，运动有助于抵消部分睡眠不足的影响。它降低了大脑中与记忆任务相关的区域的神经疲劳指标。一种可能的假设是，运动有助于睡眠不足的大脑更有效地利用其可用的认知资源。

这段20分钟的锻炼也符合“运动零食”这一更广泛的概念，尽管它比大多数运动零食的持续时间要长。运动零食指的是短时间的、爆发式的体育活动，通常持续30秒到5到10分钟不等。这些活动包括爬楼梯、快走、做深蹲或其他能提高心率的活动。研究表明，这些小幅度的运动对健康有益，例如可以改善心肺功能，甚至降低患癌症和痴呆症的风险。

获得优质睡眠的新秘诀：睡前进行运动休息

CNN：运动和午睡对大脑的帮助方式相同吗？

温：不完全是这样，在我看来，这是最有趣的发现之一。运动和午睡都能提升记忆力，但它们是通过不同的神经过程实现的。

午睡改变了睡眠不足的大脑的潜在状态。午睡组的人疲劳感更轻，脑电图上睡眠压力（一种随着清醒时间延长而增强的睡眠驱动力）的指标也更低。与这种大脑状态改善相关的指标与参与者形成新记忆的能力密切相关。

运动并不能以同样的方式缓解睡眠压力。相反，它似乎能提高记忆处理的效率。我们可以这样理解二者的区别：小睡为大脑补充了一些它所需要的睡眠，而运动则帮助大脑在睡眠不足的情况下更有效地运作。

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研究表明，白天小睡可能对大脑有益

CNN：睡眠不足的人可以用运动代替午睡吗？

温：不。运动不能代替睡眠。睡眠对身体至关重要，包括调节免疫和代谢过程，以及支持大脑的许多功能。20分钟的锻炼无法提供这些功能，尽管规律的运动确实有助于睡眠，反之亦然。

这项研究提出了一个更为具体的问题：如果某人已经严重睡眠不足，干预措施能否保护其一项特定的认知能力——新记忆的形成？就这项结果而言，在本研究的特定条件下，20分钟的运动和90分钟的午睡产生了类似的效果。

在某些情况下，这种方法可能具有实际应用价值。医护人员、交通运输工人以及其他从事安全敏感职业的人员可能会面临不可避免的睡眠不足，而且他们可能并非总有时间或合适的地方进行90分钟的午睡。短时间的运动或许是另一种保持记忆力的策略。但人们不应将这些结果解读为运动可以确保在严重睡眠不足的情况下驾驶或从事其他危险工作。

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睡眠银行可以帮助你提前休息。

CNN：这些发现能否应用于睡眠不足或经常睡眠不足的人？

温：我们应该具体说明一下测试内容。这是一项小型实验室研究，受试者是年轻健康的成年人，他们在实验室条件下连续保持清醒30小时。研究人员测试了一种特定的运动方案和认知能力的一个方面。

我们尚不清楚长期睡眠不足、老年人患有疾病或其他类型或强度的运动是否也能带来同样的益处。这项研究也没有表明运动能够恢复注意力、反应时间、判断力或睡眠不足造成的其他诸多功能障碍。这些问题需要在更大规模的真实世界环境中进行研究，尤其是在轮班工作者和其他经常睡眠不足的人群中。

萨默·卡特赖特/CNN Underscored

我每天走一万步。以下是我保持动力和避免疼痛的装备（图片由 CNN Underscored 提供）。

CNN：如果睡眠不足但当天又需要正常工作生活，人们应该怎么办？

温：首要任务是保证睡眠。成年人应该尽量保证每天至少7小时的睡眠。如果晚上睡眠不足，午睡会有帮助。如果午睡不成问题，在需要学习和记忆的时间段之前进行短暂的有氧运动会很有帮助。可以快走、爬楼梯或骑固定式自行车。

咖啡因可以暂时提高警觉性和注意力，甚至可能长期降低患痴呆症的风险，但它并不能逆转睡眠不足的影响。人们还应该规律饮食，保持均衡的膳食，并摄入充足的水分。大量油腻的食物会加重困倦感，而且应该避免饮酒，因为它会进一步损害警觉性和判断力。

人们也需要认识到这些策略的局限性，并认识到严重睡眠不足时，这些策略并不能保证驾驶或执行其他潜在危险的任务是安全的。

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