Wednesday, December 21, 2011

Jiu Jitsu


Today my body aches in an old familiar way I have not experienced for far too long.  The muscles in my core, back, and limbs cry out to be rebuilt.  I stand taller, my back is straight, shoulders swept back and my head is held high.  After one night of Jiu Jitsu I feel beat up but also stronger and confident.  The change in seasons has brought about this change in my training, good bye cycling and hello strength training and MMA.

I took up Jiu Jitsu in the fall of 2007 and have since adopted it as my winter sport.  It was easy to fall in love as Jiu Jitsu is a fast paced, intellectually challenging, social experience.  Practical experience is gained, flexibility increased, muscles are strengthened and cardiovascular performance is improved.  A better total body workout cannot be found.

Ten months of running, cycling, and swimming left me in good shape for my return but I am notably weaker.  My arms, never large to begin with, measure over an inch smaller today.  Luckily my mind has remained sharp and I picked up about where I left off.  I plan to split my time between training for the 50K trail run 4 Feb 2011 and MMA / strength training in the coming weeks.  If all goes well I can add much needed muscle and build a solid base for running.

Saturday, December 17, 2011

First Snow

This morning marked the first snowfall of the season.  There wasn't much but I have been looking forward to fresh powder so I can gain experience running in it.  I would like to do the Badgerland Striders John Dick Memorial 50k trail run 4 Feb 2012 but need to build my confidence first and see what works and does not.  The cold weather has been surprisingly rather pleasant to run in thus far.  This is all new to me so I am treading forward with cautious optimism.   
Lake Michigan bluffs with a light dusting of snow
I set out with my dog and made my way to the off road trails.   On the paved trail the way there I stuck to the grass where I could and enjoyed the feel and audible crunch of the still frozen surface beneath my feet.  There were plenty of tracks all along the trail from other trail users and animals that told a story all in themselves.  Getting to the off road trail I felt great relief and was instantly more in tune with myself, my animal, and nature.  
The trail can be seen wrapping inside the bluff
The off road trails were for the most part frozen with a rare slick patch of mud.  The entire experience was very serene yet challenging.  I kept foot turnover very high and greatly enjoyed the challenge of staying balanced on the twisting, winding, sometimes hilly path.  The workout was great with many stabilizer muscles getting put to good use they don't see on the road.
Lefty is at his best in the cold.  I wore a pack so he didn't have to.
Our run came out to 16 enjoyable miles with 4 of them off road trail.  I kept my heart rate low, stayed hydrated, and ate making the run much easier to recover from.  I plan to follow up with 16 more miles tomorrow.  The next few months will be my base period and my plan is to run 3 days a week with back to back long runs on the weekend.  Swimming, Racquetball, Muay Thai, and Jiu Jitsu will fill out the rest of the week.

Any thoughts or resources on winter trail running will be greatly appreciated by me.  It is safe to assume no knowledge of the subject on my part.  My biggest concern at the moment is footwear with respect to traction and water resistance.  I am confident there is plenty I have not thought of. 
         

Wednesday, December 14, 2011

Miami Rock n Roll 1/2 Marathon


The Rock 'n' Roll Miami Beach ½ marathon was a great experience.  The unique course offered spectacular views of the city and ocean and a few challenging inclines over the bridges of the Julia Tuttle and MacArthur Causeways.  My wife and I took Friday and Monday off and made a vacation of the long weekend.  My little sister from Tampa, her man and a friend joined us making the weekend even more epic.  This was my sisters fifth half marathon and the others first.  She is a true ambassador to the sport, recruiting two former college football stars to the world of distance running.  It was a great crew and Miami offered endless possibilities beyond racing.
Post race recovery on the beach
The trip to the start line race day was entertaining to say the least.  The night party scene was just winding down as we made it to ocean drive.  Temperatures were near 80˚F and some strong winds on the order of 20 mph had blown in.  The day before the race we all went for a short 20 minute run where the heat led me to revise my expectations for the race downward.  I have been training in the 20˚F - 40˚F band of temperatures, a whole different animal.  Don’t get me wrong, I was happy to trade the 10˚F race day weather back home for Miami.
At this point the heat left me feeling like my brain was too big for my skull
I started farther back in the first corral than I should have and had to creatively maneuver to find some space after the start.  I thought I went out too fast but I must have been downright conservative in comparison to the rest of the field as it wasn't until the 5k that I stopped passing runners and settled into a space that I neither caught nor passed anyone.  At this point in the race the heat was an overwhelming factor.  I drank water at every station and had soaked my clothes with sweat.  I have done 20 milers in the cold without a drink of water in comparison.
The love of my life on her way to a successful run following a metatarsal fracture
The first 5k featured the best bands of the run.  At the 5k the singer from Amanda Zero said “it’s a good day to run a fucking marathon”.  I have to agree with her sentiment though it was only a half marathon.  Pace was a useless metric in the heat and I was keeping an eye on my heart rate and perceived effort – throttling back when I got too ambitious.  The first bridge of the Julia Tuttle Causeway showcased my new found ability to race hills without getting owned.  I feel my focus on aerobic training has made me a much stronger hill runner in a very short time.  I cannot explain the mechanism behind it.  
My sister in the final miles
It was fun to take the long downhill from the bridge and reach mainland Miami.  It is not every day that law enforcement shuts down roads for running and I enjoyed the spectacle laid out before me.  A lot of runners began to fade before the half way point of the race as I began passing in force again.  I was happy to be applying the lessons I learned in a previously failed ½ marathon in similar conditions on this day.  Examination of my splits without context would suggest a poor race but under the conditions it was a steady effort getting stronger.                    
My sister taught me when a girl passes a guy it is called "getting chicked"  She was a fierce and talented competitor who stayed with me to the last mile but I am happy to say I did not get chicked.
Mainland Miami was a nice break from the heat.  The wind provided subtle relief without resistance and there were plenty of water stops and people spraying hoses.  Turning back to Miami Beach on the MacArthur Causeway I was greeted by the strongest headwind I have ever run into, and it was uphill.  The wind would be the main factor for the final 5 miles.  For reasons unknown to me my cadence drops when running into strong winds.  The one regret I have from this race it is not maintaining my cadence, I broke into a slight over stride from this point forward.  The loss in efficiency likely cost me a minute or two and led to increased risk of injury.

There were some long deserted stretches in here and the sun made a prolonged appearance.  I always find when races are divided mentally into fourths it is that third leg that is always the most challenging.  Add in wind, elevation, sun, and it took a lot of focus.  People kept fading and I kept pushing past.  I went for broke and pushed my heart rate near its max for the remainder of the race.
Crossing the finish line and happy to be there
I was thrilled to turn onto the final stretch and picked up quite a few spots in the last mile.  Runners were strung out in front of me and I had no real understanding of how large or small the field ahead of me was.  I was very surprised to learn my 1:32:24 effort placed me as high as it did in a field that included national elites.  A conservative estimate would subtract 6.8% from everyone’s race times under optimal conditions.  Details are on Garmin Connect.

1456 men and 2224 women competed in the event
Almost a year ago I ran my first half marathon on little training after coming back from injury.  It was an incredibly difficult effort and a horribly desperate recovery in the week that followed.  I loved the challenge and committed to improving.  Under far more challenging conditions than my first half marathon I improved by close to 20 minutes.  As this race brings the 2011 race season to a close for me I look forward to what 2012 will bring.   

There is a reason the Rock n Roll race series is popular and it is because they put on one of a kind, well organized events of high quality and reasonable value.  I would do another race in the series.      

Wednesday, December 7, 2011

Beets with Avocado and Orange


The January 2012 issue of Runners World contained a recipe for Beets with Avocado and Orange that looks delicious.  It also contains ingredients I consider exotic and as such may be better suited for a restaurant.  I have a simple philosophy in the kitchen and that is to keep ingredients to a manageable level and use seasonal produce.  It reduces waste, saves time, and money.  The photo and recipe brought me to action and I created a simpler version with what I had on hand.   

Since going Paleo I have replaced many of the grains I eat with roots, including beets.  Avocado, oranges, and beets are all staples in the kitchen these days and taste delicious by themselves or as an addition to other dishes.  The ten ingredients of the original recipe can be cut to four with good results.  Not only is the dish paleo it is also vegan and vegetarian.

Beets with Avocado and Orange.  Beets turn everything they touch purple.
Ingredients:

4 small-medium Beets
2 Avocados
11 oz Mandarin Oranges
½ Lime juiced

The Runners World recipe called for boiling beets.  I prefer roasting them as they retain more flavor and moisture.  Preheat an oven to 350 F.  Cover the beets and cook for an hour.  Let cool and peel / dice.  Peel, seed, and dice the avocado and toss with the juice of the lime.  Mix the beets, avocado, and oranges together and enjoy.  

Saturday, December 3, 2011

Embracing Aerobic Training and First Marathon

The month of November marked a decided shift in my running away from high intensity short duration efforts to long duration aerobic efforts, culminating in my first marathon this past Sunday.  I have learned a lot about endurance and myself by pushing my limits in this unfamiliar territory.  Naturally there is still much to be learned and attempted.  This is an exciting new space for me and I hope to continue to see large gains from this change in focus and concentrating on base miles over the coming months.

The best way to quantify the previous paragraph is in terms of time and heart rate.  Of course doing so cheapens the sensations and challenges that accompany actual human endurance feats, but serves to establish a reference.  Short duration represents efforts between 30 and 90 minutes.  High intensity represents anaerobic efforts at a steady pace that began greater than 80% max heart rate and feature significant cardiac drift to maximum heart rate.  Long duration reflects efforts greater than 2 hours.  Aerobic efforts are those that take place at a low heart rate and feature no cardiac drift at a sustainable pace.
                   
My most loyal training partner is tireless and unstoppable in the cool weather and has been packing our food and drink for long runs.  Here he is excited to go.
I have spent most of my life with a simple training philosophy of pushing my body to its limit quickly out of the gate and staying there as long as I can. It has served me well and I have seen much improvement in the half marathon space as such. To reach my full potential and conquer marathon plus distances I will need to better balance my training. Such heavily weighted anaerobic training has always yielded faster race times for me in short distances and comparatively slower times in long distances when using equivalent performance race tables. Conversely heavily weighted aerobic training yields the opposite result.

My first marathon was nothing special, just a training run with my dog the Sunday after Thanksgiving.  The weather could have been better at 37 F and 18-22 mph winds but to fully appreciate the best we have to experience the worst.  I split the run into three sections and took a food and water break for the dog and I at miles 9 and 18.  The first nine were easy with the wind at my back, the second nine more challenging into the wind and the last 8.2 miles were 100% of the effort.  I have never had so desperate a recovery by the time I finished.  My animal was annoyingly strong and capable.  All the details are on Garmin connect.

Cold, wet, and less excited after being caught in the rain the last hour of a 3 hour  run.
I can only describe the run as a failure, the last 10k were a terrible struggle and I found my limits well before I finished.  Had the run gone well I would have learned little, failure is the greatest teacher and as such the run was a great success.  There is plenty for me to adjust for future efforts from pacing to food and water intake etc...  Now that I have experience at this distance I can better understand and appreciate the training theory that accompanies it.              

I have long been aware of the concept of high mileage training to include recovery runs but dismissed the notion as junk miles. After failing to conquer my first attempt at a century ride, and other experiences cycling I began to rethink running. Seeing the writings and accomplishments of runners successfully utilizing high mileage training plans further fueled my intrigue, notably Britt of ChicagoRunner Girl. Excellent accounts about the merits of recovery runs by Patrick Mahoney at Endurance Athlete Project and of base training here and here by Will at An Ultra Runners Blog greatly aided in my acceptance and understanding of aerobic training. I am thankful to all for sharing their accounts.

Wednesday, November 23, 2011

Fall Harvest: Produce and Animal


It has been a couple of weeks since the last harvest of the year from my backyard garden.  It has been nice to have a steady supply of fresh herbs and vegetables much of the year.  Fresh ingredients make the best tasting, nutrient rich food and are critical for recovering from athletic pursuits.  Having processed, canned, and froze excess produce I can continue to look forward to enjoying the finished product of my labor over the winter. 
There were times the garden was both a blessing and a burden, notably during peak harvest as it takes a good amount of time and effort to process and preserve excess produce.  Any garden also requires a certain level of constant attention between watering, weeding, and harvesting.  These tasks often don’t come up at times of my choosing.  The overall experience was positive but there are things I will do differently next year, specifically including more leafy greens and fewer tomatoes.
The peppers grew well in the fall.  A collection of late season Poblano, Bell, Habanero, Cayenne, and Jalapeno peppers.
There were a lot of kitchen creations over the growing season making great use of all the fresh produce.  I never shared my failures, which, there always are but have been sharing what turned out delicious.  Every creation is listed in the food page.  Some of my favorites and most popular:


Beyond the garden, in the past couple of years I have taken up hunting and fishing.  19 Nov 2011 marked the opening day of gun deer season in Wisconsin and my second time hunting.  While I was hunting I read The Paleo Diet for Athletes by Loren Cordain and Joe Friel during the slow hours.  This paragraph brought a smile to my face:
“So what should you eat to provide BCAA (branched chain amino acids) and the essential amino acids for your rebuilding muscles?  The best possible source would be meat from game animals such as deer, elk, and buffalo.  Of course, chances are that you don’t have the time to go hunting, given your workout and career choices.  (For our ancestors, hunting was exercise and career all rolled into one activity.)  No, it’s unlikely that you will find game meat outside your back door, and it can’t be sold in supermarkets either.”
The reason game meat is the best source of protein is because these animals have very little fat in their meat and typically free range.  Their fat is layered on the outside of the meat next to the skin as opposed to a cow that has marbled fat.  Animals with a grain based diet will have greater omega 6 and lower omega 3 counts than an animal on a free range diet, making the meat of a grain fed animal inferior.  Some wild deer do eat plenty of toxic GMO corn making them a compromised nutrition source.  For this reason I hunted in swampy woodland far from farms so the deer would have a natural diet of acorns and buds.
The view from my tree stand
After putting in close to a 12 hour day the sun was rapidly fading and a steady rain picked up.  I was ready to call it a day and go back to camp for warmth and food.  Visibility was reduced and 10 minutes remained until last light when two deer manifested from nowhere right on top of me.  Seconds felt like hours as I quietly positioned myself.  Every little sound I made seemed as if it were amplified and I caught the attention of one of the deer a couple times.  I took my shot from 10 yards out after he stepped out from behind a tree.  After a pause he ran off and made it a good 50 yards where I found him the next day.  A lot of careful planning and preparation combined with the luck of an opportunity led to success.
My first deer
Deer are beautiful and elegant animals.  They are also great nutrition and delicious.  I have spent the last couple days butchering and processing the animal and plan to make steaks, stews, sautes, roasts, sausage, jerky, and chili without any going to waste.  This deer will feed my wife and I for quite some time and save us a good deal of money on groceries.

Paleo meal, inner tenderloin and salad.  I meant to eat beets as well but they took longer to cook than anticipated.
I respect these animals and understand the where and how of meat getting to the table.  It is unfortunate that we live in a world where people can live a life disconnected from this process.  I feel animal life is cheapened by the willful ignorance that accompanies many people's consumption of meat from grocery stores.  It is not just meat either, big agriculture and the FDA are guilty of horrible practices related to produce as well.   When dollars are the motivating factor many animals and workers live in undignified conditions to satisfy the demands of the market.  I can say my deer lived a good life and died humanely.         

Tuesday, November 22, 2011

Bison Chili


After years of careful study and patient trial and error I am finally proud to call a chili my own.  I have no doubt I will continue to experiment with this recipe over the years to come but the foundation has been laid.  The key to a successful chili is fresh quality ingredients in line with Paleolithic nutrition.  The best of chili will utilize only the most nutrient dense foods – meats and vegetables and avoid poor sources such as beans and other grains.  This recipe uses jalapenos but any variety of peppers diced or whole can be used to produce a wide array of great results.  I was fortunate to be able to use some ingredients from this past season’s garden harvest.

Chili Ingredients:  Meat and Vegetables
2 Tbsp Olive Oil
3 lb ground Bison
28 Oz whole tomatoes
1-2 Onions
1 Red Bell Pepper
1 Yellow Bell Pepper
2 Green Bell Peppers
10 jalapeno peppers
1 Head Garlic minced
½ cup chili powder
½ tsp Salt
½ tsp pepper
1 Tbsp red wine

Cube the buffalo into ½ inch squares and season with salt, pepper, and chili powder.  Add olive oil to a pan and heat.  Working in small batches, brown the meat on all sides and set aside in a large pot.  Browning meat in this manner brings out the most flavors in the seasonings.  Use the red wine and a wooden spoon to deglaze the pan and add the drippings back with the meat.

Core and seed the jalapenos and add to the pot.  Dice the onion and bell peppers and add to the pot accompanied by the tomatoes in their juice and the minced garlic.  Stir the mixture together and heat covered on low for 2 to 3 hours.  Alternatively a crock pot can be used.  The addition of water should be unnecessary with all the juice from the tomatoes, meat, and vegetables.  Some vegetables could be added in the last ½ hour or so if crisper vegetables are desired.  Roasting the peppers before adding would also be delicious.
Chili to go garnished with bacon and raw onion
I made up some bacon and diced raw onion for a garnish.  The chili traveled well and was plentiful.  It was extra delicious after spending some long days outside deer hunting.  I am happy to say next time I make this it will be with venison.   Improvise and enjoy.   

Ropa Vieja


My freezer has been full of tomato sauce from a large tomato haul from the garden earlier this summer.  Recently my garden provided a glut of poblano peppers as well.  This creation was driven by ingredients on hand.  My second try at Ropa Vieja turned out a well.  Recipe follows:

Ropa Vieja
2 Tbsp Olive Oil
1 lb flank steak
3 Cups tomato sauce
1 Onion
1 Cup diced poblano peppers
6 Cloves Garlic  diced
1 tsp Cumin
½ tsp Salt
½ tsp pepper

Add olive oil to a pan and heat.  Salt and pepper the flank steak and brown on each side 2-3 minutes.  Add the flank steak and remaining ingredients to a crock pot, cover and cook on low for 8 hours.  Shred the meat and serve with any number of things including Spanish rice, vegetables, or tacos.  Most recipes called for the addition of beef stock that I found unnecessary as the flank steak provides a lot of juice on its own.  Carrots and cilantro would also make great additions.  Bell peppers are typically used in place of poblanos.  Improvise and enjoy.

Thursday, November 17, 2011

Beef Oxtail Soup


I was excited to see oxtail at a local grocer the other day and instinctively bought it.  The gelatinous meat makes for great soups as well as other dishes like tacos.  The oxtail can be used to make both the stock and soup.  I made this without grains to make it paleo, though in the past I have added barley with good results.  This is a great post workout recovery meal for a cold day, reheats with ease and tastes the same as when it was made.  Prep time is low but cook time does take a while. 

Beef Oxtail
To make the stock:

4-8 oxtails
1 Tbsp Olive Oil
1 Onion
2 Carrots
2 Stalks Celery
4 Cloves Garlic
3 oz tomato paste
2 Bay leaves
½ tsp Marjoram
½ tsp thyme
½ tsp Salt
½ tsp Fresh Cracked Pepper

In a large soup pot, add olive oil and heat.  Roll the oxtails in salt, pepper, thyme, and marjoram. Brown the oxtails in the soup pot about a minute per side.  Add the tomato paste, minced garlic, bay leaves, and coarsely diced onion, carrot, and celery to the soup pot.  Add enough water to cover and bring to a low boil for 2 – 3 hours.  Reserve the liquid and oxtails and discard the vegetables.  I find a good stock and tender meat made at the expense of the crispness of the vegetables.  The soup recipe adds fresh vegetables so they may be crisp and more flavorful.   

Beef Oxtail Soup
To make the soup:

Oxtails
Beef stock
2 Tbsp Olive Oil
1 Onion
2 Carrots
2 Stalks Celery
4 Cloves Garlic
1 cup Mushrooms sliced
2 medium potatoes diced
½ tsp Marjoram
½ tsp thyme
½ tsp Salt
½ tsp Fresh Cracked Pepper

Shred the meat from the oxtails, discard the bone and cartilage.  Heat the stock and meat in a soup pot.  Add olive oil to a pan and heat on low.  Dice the Onion, carrots, celery, mushrooms, and potato and cook for 15 – 20 minutes.  Add the vegetables, minced garlic, and seasonings to the soup pot.  Bring to a low boil and cook for 30 to 40 minutes until potatoes are soft.  Enjoy.

Wednesday, November 9, 2011

Run Faster: Cadence/Over-stride and Performance

Over striding is the single largest factor in preventing runners of all skill levels from reaching their full potential.  Increasing efficiency by way of employing an optimal stride can cut minutes from race times.  Energy is needlessly wasted when over striding by two mechanisms:
  1. The leg is prevented from functioning like a spring by storing and transferring energy from one stride to the next
  2. Energy is lost to greater vertical displacement. 
This topic transcends foot strike as shod or minimalist heel and forefoot strikers are all plenty capable of over striding and the resulting inefficiency and reduction in sustainable pace that comes with it.


An over striding runner at left contrasted with an optimal stride at right.  Greater vertical displacement of an overstride can be seen by the relative magnitude of the arrows.


An over stride occurs when the center of mass is behind the knee when the foot strikes.  In extreme examples the leg is straight when the foot strikes as seen displayed by the runner at the left.  An optimal stride is one that places the center of mass directly over a slightly bent knee when the foot strikes as seen displayed by the runner on the right.

Over stride and efficiency are directly related to cadence.  Cadence being defined as the number of right or left foot strikes in a 60 second period.  An over stride / reduction in efficiency occurs at any cadence less than 90 as cited in numerous studies and is easily verifiable by an increase in perceived effort, heart rate, and calorie burn.  An optimal cadence of 90 is employed for much of the human endurance range of paces.  Even faster paces require higher cadences as stride length has a maximum.


My personal pace and cadence curve.  The endurance range of paces is a constant 90.  Outside of the endurance range speed is increased by increasing cadence.
         
Stride length reaches a maximum at sprint speeds.

Personal cadence made possible by ANT+ foot pod and compatible watch.  .  A foot pod is an underrated but indispensible training tool.

The effect of even a slight over stride on race times of all distances is profound.  Much of the year I employed a cadence of 86 preventing me from realizing my full potential.  A cadence of 90 could have shaved 56 seconds from a 5k, and close to 5 minutes from a half marathon for the paces in the table.  For the most severe over stride the potential is even greater at 3 minutes for a 5k and close to 17 minutes for a half marathon.  As paces slow efficiency decreases when over striding       

Distance
Actual Pace
Potential Pace
76 cadence
86 cadence
90 cadence
5k
6:00
5:01 (-59s)
5:42 (-18s)
6:00
10k
6:20
5:16 (-64s)
6:01 (-19s)
6:20
15k
6:25
5:20 (-65s)
6:05 (-20s)
6:25
½ marathon
6:55
5:39 (-76s)
6:33 (-22s)
6:55

The potential pace in the table indicates what pace could be realized by employing an optimal cadence of 90 if the actual pace were ran in the time listed at the cadence listed.  For a cadence of 90 no improvment is possible and the potential pace equals the actual pace.  To further explain the mechanisms mentioned at the beginning of the post:
Spring Effect:
A running human creates a good amount of kinetic energy.  Running is the closest to flying our bodies get and each stride does include an airborne portion.  The leg can capture much of the energy (63% at 90 cadence) from the vertical displacement that accompanies coming back to earth and apply that energy to the next stride.  The bones and tissue of the human foot and leg form a very functional and efficient spring.       
An over striding runner will not fully benefit from the legs ability to function as a spring.  Instead of the leg capturing and transferring this energy to the next stride some or all of that energy will be violently dissipated in the form of noise and vibration/deformation of the shoes, feet, muscle, and bones.  Run quietly is apt advice.  The next stride will need to generate this energy again requiring additional effort (0 to 16.5% + of total energy expenditure).
Vertical Displacement:
If the spring effect were not offensive enough over striding also requires greater vertical displacement, which sub sequentially requires greater effort to accomplish.  Coming from greater heights also leads to greater impact forces.  It is often repeated that races are a straight line, not up and down, thus in the interest of speed it is best to minimize vertical movement.  This effect is secondary as it causes much less energy loss than losing out on the previously mentioned spring effect.  A small amount of energy is saved from striding less but is does not change the net result.
 *
The popularity of Run Faster:  Shoe Weight and Performance helped inspire this post.  If you enjoyed this post +1, forward it to a friend, or leave a comment.  Feedback keeps me motivated.  Additionally the topic is rich and I am happy to discuss.  If you hated it or see inaccuracies, let me know too.  This post was made possible by way of mathematical analysis utilizing basic physics and efficient runner model rev 1.0.  A follow up post will contain the analysis for the select few.  If you are interested in reading more on the topic this link contains great material.  Thanks for reading.
NOTE:  An optimal cadence of 180 refers to both the left and right foot strikes in a 60 second period.  An optimal cadence of 90 refers to just the left or just the right foot strikes in a 60 second period.  Different device manufacturers and authors use either or.