Heat, Hydration and Muscles This goes into the “learned the hard way” category. Maybe you can learn from my experience. As you may recall, I had some pain in my calf a few weeks ago. Both the physical therapist and later the MD asked me if I had been running when it was very hot. I had. It was when NC was having the high heat index days and I was blogging about code red air quality. The PT said that I was probably tired and hot leading my muscles to cramp and stay sort of knotted up. I kept trying to run – thinking – well surely those knots will let go. Instead, it got worse and Monday a week ago, the pain was intense enough to send stress fracture alarm bells ringing and I have not run since (sad me). I saw the sports medicine doctor on Thursday. He told his assistant, “It’s the heat. Remember all the runners that have been coming in with pulled muscles? They get dehydrated and injured.” So dehydration was the cause. Dehydration (when you sweat out more than you drink in) impairs muscle functioning. The muscles have less blood flowing to them, are not as flexible and elastic as usual and are prone to stresses. This makes the muscles weaker, increases cramping, and injury risk. As I recall, I may have run over a root on a trail on one of those super hot days. The muscles that stabilize the ankle couldn’t handle the contraction needed to balance me. I did not feel any sharp pains – I only felt tightness the next day. My doctor used an ultrasound to evaluate my injury and found some tears in the perineum – one of the many calf muscles. I do not have a stress fracture and all my joints and muscles are strong. I did learn that the muscles most susceptible to injury during dehydration are the hamstrings, quadriceps and calf. I thought I was prepared for the. I wore a fuel belt with electrolyte water , but I guess I needed two bottles not one. BAH. Well – I am unhappy but as you’ll see in the exercise chart below – I am NOT sedentary.
I have added totals to the excel sheet that I use to make my chart. When considering my weekly total, I should not count the 80 minutes of cycling for transportation. It does not really meet the definition of exercise. That leaves me with a total of 678 minutes for the week. Within that total is my time spent on resistance or strength (weights) training. The PAG (physical activity guidelines) specify time for resistance workouts (at least 20 min 2x a week) apart from the recommendations for aerobic activity. So I should also subtract my 60 minutes of weight training form the 678 total. That leaves me with 618 minutes spent on walking, running, swimming or cycling in seven days. I averaged almost an hour and a half each day. Believe it or not, the PAG suggest that the more one exercises the better the benefit.
My change due to injury is somewhat noticable in the chart below and will be more so next week. I have added more cycling for fitness (including dirt trails) and and extra day of swimming. For the extra day of swimming (oh my gosh I used to hate one and now its three!) I am doing pool running with a jog belt. If you are interested in that, Google has some video links.
Remember you can make your own chart by modifying the excel document I made. It is available here. link to scribd
Are you still reading? Great. Let me add that I understand that the majority of people have trouble meeting the 150 minutes of aerobic activity per week, none the less 300 minutes. But it is true, the more you do the better off you'll be (for most people). Below is the statement from the PAG document itself. You can check out the guidelines in full here. There are special sections for people who are disabled or over the age of 65. However, no one gets away with being sedentary!
The benefits continue to increase when a person does more than the equivalent of 300 minutes a week of moderate-intensity aerobic activity. For example, a person who does 420 minutes (7 hours) a week has an even lower risk of premature death than a person who does 150 to 300 minutes a week. Current science does not allow identifying an upper limit of total activity above which there are no additional health benefits.