5 Not-So-Common Tips on Finding and Cultivating a Mentorship
When pursuing excellence in a particular discipline - athletics, business, academics, music, “life” in general, you name it - finding and procuring a mentor to guide and sharpen you is not a nice-to-have. It’s a must-have.
I’m not going to delve into the why of the matter, however, as I believe you already know the why.
Besides, if the one and only Gandalf had mentors during his time on Middle-earth, then you and I both need them during our time on Regular-earth. The equation is simple.
Now, while the why may be simple, the how is a different matter entirely.
Many individuals recognize the supreme value of mentorship, but often feel stymied in their attempts to actually make it happen. This could be due to a variety of factors: lack of direction (“where do I even begin?”), fear of being turned down, or, quite frankly, laziness.
In my own life, while walking down the path of attempting to identify suitable mentors and enter into fruitful relationships with them, I’ve made no small number of mistakes. Fortunately, these mistakes have birthed many valuable lessons and insights which have enabled me to, eventually, experience some pretty amazing and invaluable mentorships that I am forever grateful for.
Here are a few fundamental principles and essential ground rules that I’ve picked up during my own personal journey.
1. It’s not necessary to find the highest-level expert in the field
Say what?
This statement may catch you by surprise. After all, why wouldn’t you want an unrivaled expert in your field of interest to be the very one who personally teaches you, nurtures you, guides you, challenges you during the process of honing a specific skill set or discipline?
There are many answers to that question, but one of the most important is this: they may not be the best teacher.
[As an aside: while mentor and teacher are not synonymous, all mentors are teachers to some degree, which is why I raise this point.]
The interesting thing about true masters of a specific domain, is that they’ve been so deeply intertwined with the subject for so long that the fundamentals, the critical information that a beginner must learn during the early stages of skill acquisition, have become so deeply internalized that these basic principles are now seamlessly integrated into their actions without even having to think about them.
As Josh Waitzkin aptly put it, the foundational steps are no longer consciously considered, but lived.
“Very strong chess players will rarely speak of the fundamentals, but these beacons are the building blocks of their mastery. Similarly, a great pianist or violinist does not think about individual notes, but hits them all perfectly in a virtuoso performance. In fact, thinking about a “C” while playing Beethoven’s 5th Symphony could be a real hitch because the flow might be lost.”
~Josh Waitzkin (8-time national chess champion and Brazilian Jiu-Jitsu black belt)
What’s the point to all that? Well, this can make it very difficult for a well-seasoned maven to dig back down into the depths of their mind, in order to extricate, section out, and then teach the basal yet essential principles they learned long ago but now employ unconsciously.
It’s not that they can’t teach or mentor a student in the ways of their craft, but they may not be able to do so as well as others in the field. There’s a large difference knowing and teaching. For example, I’m sure many of you can recall a prior physics or math teacher, or sport instructor, who may have been brilliant within their craft but yet you had a difficult time learning while under their tutelage.
This concept even carries over to reading books. As I’ve sought to improve my chess game, I’ve actually found it quite helpful to not exclusively buy books written by Grandmasters (the highest achievable title in chess). You would think that a Grandmaster would be the best person to learn chess from, but, for reasons mentioned above, this isn’t always the case. For example, I have found treasure troves of insight within the works of Jeremy Silman, an International Master (one step below Grandmaster) who has built a strong reputation for his ability to teach beginners, despite the very fact that he is not a Grandmaster. It’s his knowledge of the game, in concert with his gift of teaching, that makes him shine, not the standalone fact that he’s a highly ranked chess player.
Ergo, when you seek mentorship from someone: they don’t have to be the absolute best; in fact, it may very well be optimal if they are not. You don’t need to head straight to the tip-top of the skill pyramid. Often you can find someone who is still extremely proficient (way more so than you), who will be able to instruct you and augment your learning process in a manner much more effective than even the “best” within that discipline.
Find a great teacher. Not necessarily the unparalleled expert.
2. Mentorship doesn’t have to be a formal, official arrangement
Probably one of the worst things you could do upon discovering a prospective mentor is to call them up and ask, “Hey, do you want to mentor me?” This is tantamount to you calling and saying, “Hey, do you want to take on an unpaid, part-time job?”
While I’d be remiss to assert that no successful mentorship has ever been started this way, this doesn’t change the fact that it’s still an odd way of asking. Even if they do say yes, it puts them in the awkward position of feeling like they need to plan out regimented meetings and send out a syllabus or something.
Here’s one of the most important things to know about mentors: a mentor is anyone you can learn from, who can impart wisdom upon you, who can directly or indirectly help to guide the decisions you make and actions you take. He or she can be a family member, a coworker, someone you already interact with quite regularly, or perhaps someone you only speak to on a quarterly basis. It also helps to ensure this individual is not a fool.
Some of my best and most fruitful experiences with mentors have risen out of informal relationships. From time to time, usually without it being planned in advance, they’ll provide me with a gem of seminal insight, or a particularly profound nugget of wisdom, which permanently alters my course for the better.
Should some mentorships be formal? Absolutely. But more often than not - at least during the beginning stages - it’s best to just let mentorship “happen.”
Don’t be the weirdo who comes right out and asks for it. That would be like my clumsy, ill-fated attempts to date a few women I fancied back in high school and college; rather than allowing our relationship to nurture and grow for a bit, and giving them subtle yet clear context clues of my interest, I just came straight out and asked, “Hey, would you like to be my girlfriend?”
Yeah, that rarely ended well.
3. Take a break and do something else together
Talk about things and do random crap that don’t at all pertain to your usual subject of study. Enjoy sarcastic banter and making fun of one another; grab a beer together; play a video game or chess; go on a bike ride; travel or go cliff jumping; play a sport; go see a movie or simply take a walk around town.
This accomplishes a couple things. First, it will help you connect to one another as human beings. It’s not rocket science: the more you get to know them, laugh together, and share a broad spectrum of experiences, the more you’ll be able to dismantle any personal barriers that you - often unintentionally - assemble and put up between you and other people. Within the context of mentorship, these personal barriers serve nothing other than to ultimately impede the learning process that could otherwise flourish unhindered between the two of you.
Second, and I can’t overstate this enough: it will nurture your creative processes in a profound way. Oddly enough, remaining singularly fixated on only the subject of study is not the optimal approach, even if your only goal is to learn that specific subject!
Steve Jobs knew this very fact, and summed it up well in an interview with Wired back in 1996:
“A lot of people in our industry haven’t had very diverse experiences. They don’t have enough dots to connect, and they end up with very linear solutions, without a broad perspective on the problem. The broader one’s understanding of the human experience, the better designs we will have.”
~Steve Jobs
Broaden your experiences, not just as an individual but also with your mentor. It may seem like a waste of time, especially if you’re someone who becomes intensely obsessive with that one thing you’re trying to master or accomplish, but it will be more than worth it.
4. Remember they are not infallible beings
When you highly esteem someone, heavily admire their work, and love receiving advice from them, it can be easy to arrive at the subconscious conclusion that this person is without error or character flaws, to elevate them to something of a deity and hang on every word they speak or write as if it were inerrent ideology.
Then, when they inevitably crack (or shatter) the standard of perfection you’ve set for them - say, by making a mistake, or by slighting you in some way - it’s as if the ground crumbles beneath your very feet as the world comes crashing down around you. You either become pissed off at them and write off anything they ever said as fraudulent and worthless, or stew in despair and disbelief because the person who you believed would never mess up or upset you, just did.
Like anything in this world, when you make a good thing into an ultimate thing, it becomes an idol that will eventually enslave you, let you down, or both.
Nobody is perfect, and the privilege of being mentored by someone you highly respect is always an extremely delicate balance of trusting their wisdom and yet continually remembering they are nothing more than human; at the end of the day, they are prone to the very same pitfalls and character flaws as you. If they screw up, or irritate you in some way, just relax. Take a few deep breaths, forgive them, get over it, and get back on course.
5. Your personal network: don’t ignore the power of it, and don’t neglect to broaden it
While the maxim “it’s not what you know, but who you know” may be a cliche, that doesn’t make it untrue.
Everything from crucial internships, to the job I currently hold and love, to incredible opportunities I’ve experienced, to being connected with some crazy awesome and widely-respected mentors, have all been fruit I was able to pluck and enjoy as a result of seeds planted long ago in the form of interpersonal relationships.
This is one of the many reasons it’s imperative not only to refrain from burning bridges, but also to form as many as possible. You just never know how a friend, a prior coworker, or even an acquaintance, may be able to help connect you with a reputable individual who would otherwise be all but inaccessible. You can never have a network that is broad enough.
In fact - and I’m sure I speak for my fellow introverts when I say this - keeping in mind the above sentence is one of the primary tonics that keeps me going during formal social gatherings and conventions. You know, those dreaded events which require one to endure that insufferable affliction otherwise known as small talk. I would rather swallow a live hand grenade than spend a few hours small talking with strangers who I’ll probably never see again. But again, you really never know what may come as a result of it - they may be able to help you, or you may be able to assist them, in remarkable ways.
While by no means exhaustive, I hope the above points provide a small window of clarity into the often cloudy and undefined realm of mentorships.
Agree? Disagree? I’d be curious to hear anything you’ve found helpful, be it with the actual finding of mentors, or nurturing the relationship once it’s already formed.
Percolation of Lies: Why I Hate Nutritionally "Sensational" Headlines
This is why America has no idea what to eat. This is why our collective relationship with food is so darn complicated. The following is akin to the constant stream of media articles that claim a food is horrible one week and a wonder food the next. (We all know how frustrating and confusing that is!)
Time ran an article about an Iowan science teacher, John Cisna, who ate nothing but McDonald's for three meals a day for 90 days and lost weight. It's also HERE entitled: "Man Loses Nearly 40lbs Eating Only McDonald's."
That's an extremely misleading title! While I can't blame the new sites for wanting catchy titles to reel in readers, the articles don't expound too much on Cisna's diet (or what the nutritional composition of those meals were) and they down play the plethora of other factors within his self-experiment.
A quick run-down on the facts expressed in the articles (in case you don't want to ready them). With the help of his class, John Cisna:
1. Constructed 3 meals based on a 2,000 calorie diet and the recommended intakes for protein, carbohydrates, and fat by the USDA (which I think are bunk, but that's a whole 'nother ball game).
2. Walked 45 minutes per day (when previously, he was doing no extra physical activity)
3. Resulted in a 37 lb weight loss and a drop in cholesterol from 249 (dangerously high) to 170 (decent level). His LDL dropped from 173 to 113. (also insanely high to an ok-level).
I'll state the glaringly obvious that, any a man who was quite overweight to begin with (280lbs) performing NO extra physical activity, and was probably over-eating anyway, WILL lose weight with calorie reduction and added physical activity. That's just physiology. At this point, ANYTHING he does towards reducing his calories and increasing his exercise will produce weight loss. Also, the cholesterol reduction is a result in the weight loss, not necessarily the food he ate. Can you start to see why this title is misleading?
To quote the man himself, "The point behind this documentary is, Hey, it's (a) choice. We all have choices. It's our choices that make us fat, not McDonald's." source
On one hand, I agree with Cisna; we are not victims of our environment, we do have the option to choose healthier foods when out to eat. No one forces us to purchase a Big Mac over a salad. It is imperative that we be wary consumers when fast food is involved (the food companies strive to make their food palatable, cheap, and addictive) and Cisna proved that when one digs a bit and is aware of the caloric values of food, that empowers us to make smarter food choices.
On the other hand, the real message is convoluted and lost amid that headline. It presents the situation as a justification for choosing McDonald's instead of a home cooked meal. Or instead of a meal composed of WHOLE, minimally-processed foods ('cause I guarantee that McDonald's has very few whole foods on the menu.). Conveniently, you can read along with this handy ingredient guide. You'll want to refer to this as we move on.
Cisna admitted to having double cheeseburgers and a Big Macs throughout the experiment. Hmmm... Big Macs have roughly 29 grams of fat (and not the good kind check out the "Big Mac sauce"), 46 g of carbohydrates (definitely not the minimally processed kinds, look at the guide under "regular bun"), and 25 g of protein (but, really, where does that meat COME FROM?)
"Yeah Kelsey," you say, " we already KNOW that's not a 'healthy' choice." Fair enough, let's take a gander, shall we, at the yogurt parfait he ate regularly:
2 g of fat, 30 g carbohydrates, and 4 g of protein. Once again, I question the quality of the source of the fat and protein (from the milk). I can't imagine that the milk used in that is really that great. However, that is overshadowed by that 30 grams of carbs, that is, SUGAR. Highly processed, sugar (though there's a smidge of natural sugar in the milk and fruits, but it's NOT 30 grams worth). Don't believe me? Look up yogurt and granola in that handy guide. Ick. Sugar has, time and time again, been shown to be a culprit in increasing inflammation in the body and creating insulin resistance (to keep the list short), both of which are risk factors for Type 2 diabetes. The same criticism rings true for the maple oatmeal he ate, except that little bugger has some light cream in it... yum!
At first glance, the Eggwhite Delights that Cisna consumed seem like a good idea, only 250 calories each, oh but wait, check out the "whole" grain muffin and egg white and margarine ingredients. Super appealing right?
I could continue in this vein for a while, but I'll cease my tirade and allow my point to actually surface: 240 calories of crap is still crap. The composition of food absolutely matters. The message, as it stands on the surface, is still, "reach for processed foods over whole foods." How much BETTER do you think Cisna would feel if he had chosen whole, minimally processed foods?
I applaud Cisna for sticking with his endeavor, to keep walking even when he didn't want to, and to making conscientious food choices. I'm so glad he lost weight, is healthier than before, and has learned the value in monitoring caloric intake. This is a great stepping stone on his path to a healthier lifestyle. I hope very much that he will be able to continue without the help of McDonald's.
I think the true message of this experiment is food quantity and quality matter, along with regular exercise. Unfortunately, the second half, food quality, is buried under the lie that choosing "healthy" options at McDonald's is a viable way to improve health. Again, crap is still crap. Don't let the media's sensationalism divert you from the truth of eating real foods.
"That's A Load of...." Debunking Media "Fitness" Terms
Glance at the front of the magazines at grocery stores and you'll see a variety of "fitness" or "health" claims such as "tone," "fat-blasting," and other such nonsense as that. I find myself rolling my eyes so much that my occipital (eye) muscles are as big as a body builder's biceps. Sorry, strength coach joke.
Moving on, today I'm going to rip through debunk a few of those outrageous claims so that you too can strengthen your occipital muscles as you wait in the grocery check-out line. I can not possibly cover all the silliness out there, but I've narrowed it down to a few of the common ones (that seem to appear month after month on magazines such as "Self" or "Woman's Day"). A lot of these claims are found on women's magazines, mainly because I think we're fed more crap than the fellas, but they apply to both genders.
CLAIM: "Tone," as in "tone those jiggly arms"- First off, let me remind you that everyone's arm jiggles; that's what happens when a muscle is relaxed. The main definition of "Tone" in exercise physiology is: the normal state of elastic tension or partial contraction in resting muscles. For example, the postural are constantly contracting and relaxing to keep you upright (or slouched...stand up straight!). The fitness magazine "tone" refers to the ability to actually see the muscles' shapely form. (So really, they should say "definition" not "tone.")
In order for a muscle group to be defined, say your arms, two things must occur: 1) the muscle is big enough to be seen (so those stupid tricep kick-backs or bicep curls with 5 pound weight ain't gonna cut it when it comes to muscle growth.) and 2) there needs to be less subcutaneous (under the skin) fat. How does one accomplish bigger muscles with less body fat? Why, picking up heavy stuff and eating a vegetable and protein laden-diet! Glance through a women's magazine at those "arm toning" exercises and you tell me if you think they would actually succeed. As for eating healthy, the details look different for each person (i.e. paleo, vegan, omnivore, etc.), however it should be 90-100% REAL FOOD with minimal crap (though a Christmas cookie or two is ok.) 90% of the time.
FACT: "Tone" means: less fat, bigger muscles.
CLAIM: "Fat-blasting" food- The media makes it seems as if these foods (and it's a new one each week!) has heavy artillery and upon entrance to the body, starts blowing up fat cells left and right.
Uh, sorry, that's not how the body works. Fat cells, once formed, don't go away. They do however change size depending on how much fat is stored in them. So, in order to reduce the amount of fat in each cell, the body needs to be in a caloric deficit. This means you need to eat LESS than what you're using up, for the basic metabolic functions, exercise, and other activities. The body will burn it's excess energy, aka stored fat, to make up for the lack of energy intake. Altering body composition is a life style change; I guarantee you that just eating a serving or two of "fat blasting" foods will NOT be enough to reverse years of bad eating habits. There is a wealth of solid (and scientific) advice out there, and there are definitely more details than I plan on elaborating in this post (maybe another time...) however it boils down to this:
Stop eating crap, eat real food, and pick up heavy things. Take note that I put the nutritional advice first. You can not out-train a crappy diet, so clean that up first! There will be a blog post later on this month regarding that whole aspect of fat-loss.
FACT: Eating a whole-foods based diet, with minimal crap, and exercising regularly OVER TIME will reduce body fat levels.
CLAIM: "Target" body part, usually for fat loss- This myth just won't die! It keeps reappearing week after week on the covers of magazines and on the interwebz. People, YOU CANNOT SPOT REDUCE!!! The body doesn't say, "Oh, I see that you are doing thousands of crunches, I should reduce the body fat I store there so you can have a flat tummy." Really, it says, "For the love of all things iron, STOP CRANKING ON THE SPINE ! It HATES that!" Targeting is about as effective as trying to grow eye-stalks.
Oh, if grunting made it so!
For "targeting trouble areas" see the above two points: an overall body fat reduction will promote definition of muscles and those "problem areas" will be not so problematic. Again, it's a life-style change, not a quick fix.
*This is not to say that isolation work has no purpose. How else are you supposed to have guns for the ladies? Some isolation work thrown in to an already compound-movement heavy (lots of multi-joint exercises such as squats, deadlifts, pushups, pull ups etc) work out can provide some extra stimulation to a muscle group that can lead to hypertrophy (growth).
FACT: Compound movements should be the bulk of you training program. That combined with a diet of whole foods will reduce body fat levels and thus reducing the need to "target" certain areas. (anyone picking up on a theme?)
CLAIM: This is an actual quote from a celebrity trainer, who is a disgrace to our industry:
"Oftentimes, heavy weights can tear the muscle fiber causing it to bulk, but using a lighter weight for a longer duration and allowing your body to move in many different ways to target all of the muscles will lengthen them without tearing."
-Tracy Anderson
Multiple other coaches and trainers have ripped into this (and other nonsensical claims that spew forth from her mouth). Sadly, she is not the ONLY trainer out there who thinks this is true, she just happens to profess this poop where more people can read it. I'm not going to touch the first half of that statement except to say, uh, that's the method by which the body grows stronger...by tearing and repair muscles. Oi!
The phrase "lengthening muscles" is also found, unfortunately, in other fitness "experts" mouths and in their writings. It is physiologically impossible to lengthen a muscle without breaking the bones and extending them or altering the attachment points of the muscle. Yes, the muscles lengthen and shorten during normal movements, however, the actual length of the muscle doesn't change. Got a problem with that? Take it up with your parents, they passed the genes along.
I think that term is really just "tone" said in a different way. Ultimately, the phrase is intended to indicate "definition" just like the word "tone." If a trainer says/writes that claim, it's a pretty solid indication that the trainer/coach has absolutely NO idea how physiology works and therefore you should turn and flee. I'd also like to note her splendid use of the buzzword, "target."
FACT: "Lengthening" a muscle is impossible, and the intended implication is "definition" which is attained via the methods described ad nauseam above.
Now, my SAPT readers, you are armed with the knowledge to see through the baloney that fitness magazines and products proudly display and you have the ability to recall the truth: a great, healthy body is created by... do I really need to say it again? Don't allow the stupidity of the outrageous claims dissuade you from thinking that anything but consistent hard work (both in the kitchen and in the gym) will accomplish your performance and/or physique goals.
Maximize Each Workout: Train Like No One is Looking
Potentially - or probably - the biggest barrier keeping most people from making progress on their goals (fitness, build muscle, fat loss, strength, etc...) is their own state of mind. That feeling like "Oh, people are watching me, so I don't want to [X]..." [look like I'm trying], [fail], [struggle], [make a weird face], etc. But, all this self-limiting behavior successfully accomplishes is self-limiting progress. I've trained all over the place in a multitude of different environments and have often been seen doing off-the-beaten-path type exercises. But, even I sometimes get a little nervous about the liklihood of drawing attention to myself. When that hesitation kicks in, here are my top 3 reminders to keep my self-limiting behavior out of the way of accomplishing my goals:
1. No one is looking. Most of the time no one cares what you're up to in your daily workout and they really are not watching. Trust in this first rule.
2. Don't let your assumptions of someone else's perceptions affect your behavior. Okay, so you're doing something attention grabbing (read: weird) in your workout. Yes, you will probably catch a few eyes, so if #1 isn't working for you. Then ask yourself this: "So, someone is watching me train, why would I stop just because they're watching?" They're probably watching to learn something new. That's what I've found over the years. No one has ever approached me to tell me I'm "wrong" - rather it usually means I'll get to have a conversation with someone new about whatever it is I'm doing. They want to learn!
3. The world doesn't revolve around you. At least in the realm of weight training - I can't actually speak for other areas. This is really the bottom line. Whether you like drawing attention to yourself or dread it, the world doesn't revolve around you. So, keep your eyes down and power through on taking a small step towards whatever is going to help you accomplish your next goal.
The point in training for fitness, building muscle, or strength is making progress towards personal goals and achieving things you, personally have never achieved before. Don't allow those self-limiting behaviors derail your success!
Give Me Strength!: The Process
It hurts. The short-term effects from strength training often leads to pushing the body to places the mind may not want to go. But, if the mind is open and willing, the body can be pushed to places it may not realize are possible. Strength-training, like any activity, requires a detailed process, which focuses on daily progression. Below are three tips to help your mind stay right as you get your body tight:
- Goal-Setting: It’s imperative to have daily, weekly, and monthly fitness and strength goals. These should not just be based on weight loss/gain or amount of weight lifted. Instead, there should be deliberate practice goals, which focus on progression. Focus on the process of improvement rather than simply end results. Examples: Daily - Commit to trying one new exercise [pick one to help you put extra emphasis on a weak area or an area you enjoy training] for each daily training session for a month; Weekly - Commit to a weekly schedule of weight training, avoid a haphazard approach... what time does your workout begin? Don't be late!; Monthly - Did you achieve your daily and weekly goals? What does the next month look like, what are you planning to accomplish on a daily level? Is it time to do a quantitative test yet?
- Willpower Talk: Use committed words like “will” over words like “gotta”. Direct attention to what you will do rather than what you gotta do. The more you talk about will the more you will get. For example, what is your weakest area that you WILL improve to build muscle and strength? A lower body unilateral exercise, perhaps?
- Expectation Scorecard: Create a scorecard for yourself to grade your mental performance during a strength-workout. Have categories like attitude, positive self-talk, energy management, etc. so that you will grade your mental-toughness. This will hold you accountable to maximizing performance.
A couple other things to consider: what is your pre-workout preparation? It probably involves some foam rolling and a warm-up, but are you preparing your mind to take full advantage of the soon to start training session? Are you fully focused when the first set begins?
Like most things in life, success in strength training, fitness, endurance training, fat-loss, etc. is at least 50% mental. The process of engaging in a long term progressive program also teaches excellent (mental) practices that translate into many other areas of life (discipline, goal setting, enjoyment, commitment, etc.).
Circuit Training for Fitness
Picture this:
You got out of work later than ususal... perfect timing to hit rush hour at its height and extend your normal 20-minute commute to the gym into an all-out 45-minute crawl full of frustration.
By the time you get to the gym, you only have about 25 minutes before you need to leave.
What do you do? Do you literally throw in your towel and just go home? How can you possibly salvage a decent training session out of the train wreck that was the afternoon?
Circuit Training is waiting to save the day! Well, so are Time Turners, but pretty much no one has one of those things...
What is Circuit Training?
The possibilities are limited only by your imagination (and your physical capacity. I know from personal experience that performing box jumps after a barbell sumo deadlift is a baaaaad idea).
Typically, circuits are comprised of 5-8 exercises and you want to work with weights about 75-80% of your max. Translation: pick weights that you could probably perform for 8-10 challenging repetitions. String them all together, and work through the circuit with minimal rest between exercises.
In terms of time, you can set up your circuit a couple of different ways:
1. Set a particular rep goal per exercise and then set your time for 15-25 minutes and see how many rounds of the circuit you can perform.
2. Pick a number of rounds to complete and try to finish as quickly as possible. Usually, if you have about 5-8 exercises, 5 rounds will be around 20-ish minutes.
Benefits of Circuits:
1. They're a great way to improve overall conditioning without watching your hard earned muscle mass wither away. Two recent research reviews (abstracts here and here) have found that steady state cardiovascular training can a) decrease power output (yikes! Not good for athletes that need to produce power aka: everyone) and b) compromise muscle mass (and thus strength) gains. This effect is seen most prominently when aerobic training is 3x/week for greater than 20 minutes. The metabolic pathways that aerobic and anaerobic (think strength training and sprint/interval training) are conflicting. It's very hard to maintain a large amount of muscle mass and be a long-distance runner!
Circuit training is similar, metabolically, to sprint/interval/hill training in that it preserves lean muscle mass.
Steady state cardiovascular training, on the other hand, can lead to elevated levels of cortisol (stress hormone) which can decrease the effectiveness of muscle-building hormones such as testosterone and insulin-like growth. It also encourages muscle protein break down.
While strength training too breaks down muscle tissue, the anabolic (building) environment produced by strength training encourages repair more than the catabolic (break down) environment of aerobic training. Strength coach Charles Poliquin says:
Whereas endurance exercises compromise anaerobic performance and body composition, anaerobic training modes such as sprint intervals and weight lifting will benefit endurance athletes if programed properly. To improve endurance performance, do a strength-type resistance training program with loads of 80 percent of the 1RM or heavier. This will train the type IIA muscle fibers so they increase the rate of force development and get faster.
Type IIA muscle fibers = strong, powerful muscles. We want those!
So if you're still with me, we'll move on to the second point.
2. It's time-efficient. After a quick dynamic warm-up and maybe a warm-up set or two of the planned exercises, the total time of a circuit should be no more than 25-minutes start to finish. 15-minutes would even be sufficient depending on the intensity of the exercise selection and weights used. Nice huh? It's just long enough to make you feel like you've worked out but not too long that you're home late for dinner.
3. (but really 2.5) Not only are they time-efficient but they're efficient in the sense that a circuit can hit a lot of muscle groups, through full ranges of motion, in one fell swoop. While a jog will really only get your legs (and, I would argue, not very well since the range of motion is small, the force production is low, and the intensity isn't that high either) and maybe some low level core activation, a circuit can be full body. Take a look at this sample:
Goblet or barbell squat x 6-8
Pushup x 8-10
Step back lunge x 6-8/side
3 Point Row x 8/side
Kettle bell swing x 10
Can you see the total body genius in that? We have lower body (both bilateral and unilateral movements), upper body (push and pull) and a delightful amount of full range of motion exercises. All of which, if one wanted, could be done with just one kettlebell.
Run through that baby 5 or 6 times and try to tell me that's not cardio. Oh wait, you can't. I can't hear you over your screaming lungs and gasping breaths.
4. Because circuits demand so much from your muscles and cardiovascular system, they're pretty calorically expensive, which means your body will be burning calories longer post-workout than they would after a lower intensity training session (aka: low-intensity, steady state cardio). On those above-linked research reviews, it was found that athletes reduced body fat when they performed high intensity exercise (sprints or circuits).
So, if you're looking for an efficient way to reduce body fat, preserve lean tissue, AND improve your cardiovascular fitness, circuit training is definitely a tool you want in your toolbox!
I feel obligated to note that strength training, solid strength training sessions, need to make up the bulk of your training week. Picking up heavy things repeatedly is the best way to build muscle and get stronger. Circuit training, while it won't make you weaker and can aid with strength gains, is inferior overall to 80-90% max lifting in terms of producing maximal strength gains. While I don't recommend basing your entire training plan around circuits, they are beneficial and even fun (yes, fun.) to throw in every once and a while.
