I have been running for almost 2 years now, after pretty much never running before in my life. I have had the usual injuries (shin splints, sprained ankle, etc.), but nothing serious. I've always thought I was doing everything right, until I saw this video about the day after the marathon:

<http://www.youtube.com/watch?v=m-hCuYjvw2I>

The thing is, my thighs have never - not once - hurt after a run! My calves have hurt, as well as my feet, hips, etc. So what am I doing wrong? Or am I doing anything wrong at all?

Some sites suggest this could be because I have weak thighs, and the rest of my legs are picking up the slack. But I can comfortably leg press about 3 times my body weight, so I don't think that's the problem. 

Is this something to be concerned about? Or is it just marathon specific: I mean, I've never run more than a 10K.
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The main differences between the two is the philosophies behind it, and how they are designed to work. First and foremost, it is important to realize that Paleo does allow carbs, just not grains and legumes (or anything that grows underground).

**Atkins**

* Is a ketogenic diet. It puts your body in a safe version of a fasting state so that your body turns fat into ketone bodies. Ketone bodies cannot be reassimilated to fat so unused ketone bodies are urinated out.
* Emphasis is on both protein and fats. Protein is there to help protect your muscle mass, and fat is used to provide some additional energy.
* Is designed as a temporary diet to help you lose weight, it is not intended for prolonged use.

**Paleo**

* Is based on what scientists believe the average paleolithic man ate. This includes berries and easily accessible fruit/vegetables as well as meat.
* Emphasis is on avoiding processed foods and foods that are likely to cause digestion problems. This includes grains (like wheat), tubers (like potatoes), and legumes (like beans).
* Is designed as a way of life diet, or in other words a sustainable diet you can use for the long term.

There are some commonalities between the two approaches, such as the emphasis on meat as a protein source. However, Paleo tends towards whole foods and grass/natural diet fed meat and Atkins makes no distinction. While Atkins does not allow carbs which would take someone out of ketosis, Paleo does allow carbs.

Anyone who exercises regularly will need the following for a healthy diet:

* About 1g protein / lb lean body mass. This is both for the better thermic effect of food (i.e. it burns more calories digesting it), and for restoring muscles that have been torn down by exercise.
* Carbs on workout day. This is a minimum, as it helps restore your glycogen levels to help you recover more quickly.
* A combination of saturated and mono-unsaturated fats. Fat is used for energy, but it also carries with it essential fat-born vitamins. NOTE: I did not include poly-unsaturated fats which are man-made and cause health issues over the long term.

How you proportion those depends on your daily caloric needs, but it is safe to split the remaining calories after you have your protein evenly between the carbs and fat. This is very possible on the Paleo diet, but due to the way Atkins is designed it is not possible on that diet. You will likely need to alter how you exercise on Atkins to ensure you do not burn muscle.
Berin Loritsch is mistaken in that Atkins would be meant only for weight loss. It is meant for prolonged use as well as any reasonable diet.

In Atkins you drop the carbohydrate intake to max of 20 grams per day for two weeks. After that you start gradually adding carbohydrates to your diet until you reach the point where you stop losing weight. Then you dial the carb intake back until you have reached desired weight. After that you can raise the carb intake a bit to a point where you don't lose or gain weight. The most probable mechanism for losing weight with Atkins is lessened hunger due to eating less carbs and more importantly more protein. This leads to less energy intake, leading to weight loss when the energy intake drops below energy expenditure. [More detailed description about different phases of Atkins](http://www.atkinsdietfreeplan.com/).

Paleo diet is basically based on some anthropology-based ideas on what some people ate during the paleolithic era. The basic idea is that this would be the diet we evolved to eat, so based on that it should be good. The problem is that people living in paleolithic era ate extremely varied diets based on where they lived. The diet itself is basically various meats and vegetables. Depending on whose paleo ideas you follow dairy and grains are allowed/disallowed. Generally on paleo diet you eat less carbs than is common these days. There are lot of sites about paleo around. Most prominent gurus are propably Dr. Cordain, Mark Sisson and Robb Wolf among others. 

Neither is really much evidence based (unsurprisingly little about any diet is). My advice would be that if you feel fine on one of these, then go ahead. You should take any health claims made on behalf of either approach with grain of salt. Though restricting bad carbs is good, there is lot of hype based on little evidence about either one.