Is a monk allowed to exercise the body in order to keep it fit and healthy? I reckon both 'healthy' and 'fit' as attachments, but is there an overall rule/teaching that explains this?
Healthy and fit body does not need to be seen as an attachment. If a monk took the Bodhisattva Vow, all his activities will be done with the wish to benefit others. A healthy body is actually a very useful tool if one wants to help other beings. During a long life free from illnesses one can do much more than during a short life with numerous visits to doctors and hospitals (which are usually costly). Precious human body is also a topic of various teachings (see this or that) which invite us to realise how rare it is to obtain a well-functioning human body and how easy it is to lose it. With that in mind, maintaining a healthy body is a very wise thing to do.
In Tibetan Buddhism one of the main meditation practices involves doing physical prostrations. In Vajrayana traditions all practitioners - monks and lay ones - need to complete at least 100.000 prostrations as a part of preliminary practices. Some practitioners continue to do prostrations on daily basis and even Dalai Lama admitted that he indeed does them every day.
The Dalai Lama takes daily exercise, including walking on a treadmill if it's too wet to walk outside -- http://www.dalailama.com/biography/a-routine-day. It makes sense to me since given that this human life is very precious in that it gives us an opportunity for moving towards enlightenment, it follows that it's a good thing to keep the body alive for as long is reasonably possible.
Yuttadhammo gives an interesting view on the whole exercise thing here: https://www.youtube.com/watch?v=qJifR6EGTb8. He says that physical exercise "doesn't play any part", certainly for an enlightened being although I think he was also referring to people who want to become enlightened. But I think his overall point is one of adequacy. He doesn't deny that it's useful to, for example, eat enough so as to be able to meditate, but his position appears to be that there is no point beyond that.
In his wonderful book "A path with heart", by Jack Kornfield, the author, himself a Buddhist monk under Ajahn Chan for several years talks about exercise and several other normal things monks ignore in order to pursue enlightenment single mindedly. He advises against this extreme behaviour, and urges monks and spiritual seekers to not ignore normal healthy living.
He recounts interviewing several monks who suffered from diabetes and other lifestyle diseases that came from not eating healthy food, from not exercising, from developing an aversion to their body and consequently not caring enough.
That said, Zen monks and nuns in the tradition of Thich Nhat Hanh perform the ten mindful movements as a group daily. It is a slow exercise set to be performed with mindfulness. In itself it is a meditation, when performed so beautifully by the monastics. His order breaks with tradition in several ways, including allowing monks to cook their own healthy food instead of depending on donated food. A logical thing to do in this age. Someone at plum village told me that they used to get catered food but it made everyone sick often, so Thay changed the rules to allow monks to take turns to cook their own healthy vegan food and eat thrice a day. The monks also modified their uniforms from traditional Vietnamese dresses to suit the French climate.
Perhaps in times when monks only walked around from place to place, that was more than enough exercise. In modern times, especially in countries like Thailand where monks often live in cities, and can ride for free on buses, trains where usually someone pays their fare, or offers a ride, walking is minimal. Plus, devout people often offer rich or special food into the monk's bowls because they think it gets them extra merit. So food for survival gets turned into abundance. Eating a single meal a day means the body goes into glycemic shock after the meal, which can affect the insulin secretion adversely in some.
Bodhidharma according to some accounts allowed his legs to rot away by sitting in the cross legged posture for nine years. The cross legged position can cut off blood flow, which isn't a problem for a few hours, but if a monk sits in this position regularly for hours, bad side effects maybe expected. Such attitudes and role models don't help.
Health is the greatest gift, contentment is the greatest wealth, a trusted friend is the best relative, Nibbana is the greatest bliss. - Dhammapada 204
For a lay person, moderate exercise, moderate diet and good hygiene can be considered as part of the middle way that the Buddha taught in the Dhammacakkappavattana Sutta, as it contributes towards the maintenance of one's health, which is beneficial to practice.
"There are these two extremes that are not to be indulged in by one who has gone forth. Which two? That which is devoted to sensual pleasure with reference to sensual objects: base, vulgar, common, ignoble, unprofitable; and that which is devoted to self-affliction: painful, ignoble, unprofitable. Avoiding both of these extremes, the middle way realized by the Tathagata — producing vision, producing knowledge — leads to calm, to direct knowledge, to self-awakening, to Unbinding.
In the case of monks, the Buddha explains in the Sukhamala Sutta:
"Drunk with the intoxication of youth, a monk leaves the training and returns to the lower life. Drunk with the intoxication of health, a monk leaves the training and returns to the lower life. Drunk with the intoxication of life, a monk leaves the training and returns to the lower life."
Despite this, I can still find some example of a monk trying to get light exercise, in the Meghiya Sutta (below). This leads me to think that light exercise without "intoxication of health" might still be considered acceptable to monks.
Then in the early morning, Ven. Meghiya adjusted his under robe and — carrying his bowl & robes — went into Jantu Village for alms. Having gone for alms in Jantu Village, after the meal, returning from his alms round, he went to the bank of the Kimikālā River. As he was walking up & down along the bank of the river to exercise his legs, he saw a pleasing, charming mango grove. ...
To keep the body in good health is a duty, otherwise we shall not be able to keep our mind strong and clear. ~ Buddha, 563 BC to 483 BC
"Monk" is a broad term and I will interpret it as "layman", not as a monastic.
Traditionally though as said other places, walking exercise is the main form of exercise for monastics. Let's also not forget that monastics also begged for food, roving all over the villages, another form of exercise.
Back to the present moment: we are a sitting generation. Both of my jobs are completely sedentary and involve the computer. Most sought-after jobs nowadays involve staying in one spot be it in manufacturing or entertainment.
Studies show those who stay still for more than 6 hours per day do not get the blood flow they need and lose decades off their lifespan--probably in addition to adopting other bad lifestyle factors.
This is a major reason why I am watchful of my physical activity levels and overall state and have many emotional and physical management techniques.
I am certainly not as realized nor have I devoted enough retreat time to be worth anything in the Buddhist level of experience but... I strongly encourage all my fellow Buddhists to adopt non-Buddhist energy balancing practices including exercise but also mental visualization and nature cleansing.
Also, "healthy" and "fit" are not attachments in this case. They are prerequisites for cultivating the Way.
The Buddha proclaims the importance of doing ANYTHING that will encourage healthiness as well as longevity. (See my answer to someone's question about drinking for an excerpt.)
This is why the Buddha encourages things like the brahmavihara practices (metta, karuna, upekkha) and dhyana (jhana, samadhi) practice even though they have nothing at all to do with Enlightenment, the Ultimate, finding your True Self/Nirvana/Emptiness and cutting off the root of suffering.
On several accounts the Buddha commanded certain people to stay in the world (avoiding death) until Maitreya's arrival. Mahakashyapa is one of them, lying in Chicken Foot Mountain. Is this a form of attachment?
No, it is not, because they have been commanded to do so. Just so, your truest desire is to Awaken is it not? This is a command from the Buddha within, a command which encourages everything necessary to continue cultivating and making more time for cultivation by becoming healthier physically, emotionally, financially, mentally, and socially.
Care for the physical form is absolutely crucial to the great Eastern endeavor for Awakening and Immortality: tai chi, chi gong, kung fu, chakras, kundalini, chi mai, gong-fu (super powers), acupressure, tcm... these were all originally created by people with high dhyana attainments or as gifts from aliens (heavens).
If the body isn't your friend on the path, then it will be your obstacle!
The way I integrate physical practices is not completely coverable in a text-based Q&A but go to my Youtube page Bodhisattva Lifestyle where I have posted and will continue to post videos, with many exercise instructional videos planned.
The following are exercises (some energy-based) I integrate into my exercise session: grounding, nature cleansing, martial arts, tai chi postures, up-side down pushups, running, tricking, and some rare participation in athletic activities.
During my exercise session I will take breaks when getting breathless, oftentimes mantraing, mudraing or doing short sessions of samatha or vipassana.
These practices reset my energy levels, moderate my mood and prepare me for meditation. It also makes me more courageous. These fundamental energies are important factors in meditation. See: The Five Faculties. I emphasize this because these energies are crucial to balance at the beginner to advanced levels.
I will put here one exception to my encouragement for exercise: those who have mastered a high stage in meditation (stable dhyana levels) do not need to exercise because they do not generate the negative poisons that most people are constantly generating (which needs purification) anyway. Such people can also control their heart rate and their cardiovascular system, among other chi effects not worth discussing but all of which may help the person to be able to sit even longer periods of time.
Householder Jordy van Ekelen, interested,
it's not proper for a monk to exercise the body in ways householder do, especially today. Also many "wanna be" traditions may do it. There are also cases where Monks teach lay people such. Both is not proper.
In the case of teaching such to householder, it's also easy to assume that there are grave wrongdoings till corrupting families involved. Monks and communities making a living on such, are not regarded by good monks and good communities and as it points a total wrong light on the way out of suffering.
Usually by walking, sitting, standing, lying, mindful on the body, by the usual required bodily tasks, the body of a monks stays naturally health as it is proper for the practice.
Moving the body and parts of it in wrong ways under householder would be a transgression for monks. In regard of the practice such as kammic not so good effects even not counting as wrong doings in regard of Vinaya.
Once one follows a livelihood in tune, once following right livelihood, such compensations of wrong are not required anymore. How wrong livelihood of modern people actually is, is best shown in the increasing of seek after wellness-compensations.
Although there are many today who follow ways of householder, do favors for householder, follow their trends to gain and maintain a market, one is wise not to regard such as the way of the good following disciples.
(Note that this gift of Dhamma is not dedicated for trade, exchange, stacks or entertainment but as a means to make merits toward release from this wheel)
If your spiritual life suffers from your weak body, wouldn't you do physical exercises? Yoga is the best practice to have a strong and healthy body. Strong physical body is a key element for achieving top results in any field of activity. Senna, the legendary F1 driver, did strenuous physical exercise to keep his body fit and perform at the top level as a racing driver.