October 2019

Step Frequency, Knee-joint Forces in Female Runners

Running is mostly good for you. Studies have repeatedly demonstrated cardiovascular, metabolic, mental and musculoskeletal benefits galore. Furthermore they have recently shown that running does not cause knee osteoarthritis unless….you have had previous injury, poor mechanics or obvious alignment issues. Knee injuries are common in runners, more common in female runners, and fewer women run past their 50s. Might stride frequency be a factor here?

A US study looked at stride frequency (SF) and tibio-femoral joint (TFJ: knee) shear and compression forces among recreational female runners to see if those with the highest SF had lower TFJ forces at impact.

Fifty-five healthy runners ran at a designated speed (6.67 mph) on an instrumented treadmill that could measure impact forces at self-selected SF’s.They were divided into tertiles of low (<166 steps/min), middle and high (>178 steps/min) SF’s. 

Consistent with other studies that compared SF, this found that those who ran at high SF actually had the lowest anterior shear forces, compression forces and medial compartment (inner side of the knee) forces while those who ran with fewer strides/min had higher knee forces.

This is not unexpected. Running the same speed with fewer steps means the athlete is taking longer strides per unit distance. Longer strides means both pushing off with more force and landing or hitting the ground with more force. Other studies have suggested that shorter, more frequent strides may actually minimize the forces that contribute to knee injuries. This one seems to support that contention.                        

MSSE July 2019

Calculate Your Weight-Training Calorie Burn

Most folks know that they can count on about 100 calories burned for each mile run. If you walk a mile, it’ll be about 85 calories. Data varies for a variety of exercises and activities but now a Texas study has calculated a prediction equation for calories burned during a resistance training routine. Of course, you’ll have to do the same one used in the study but it’s a pretty sound program.

The 52 healthy, active subjects (27 men) ranged from 20-58 years old, but the authors don’t tell us if they were experienced lifters or not. They were pre-tested on a variety of anthropometric and physiological factors including body composition and aerobic capacity. Three days later they were strength tested on 7 common exercises: leg press, chest press, leg curl, lat pull down, leg extension, triceps presses and biceps curls. Their predicted max on each exercise was used to calculate the training load.

They did a warm up set followed by 2-3 sets of 12 at 70% of their maximal ability with 2 minute rests between sets. Oxygen uptake was measured directly during the entire workout. The following regression equation gave a good estimate of calories burned. Total net calories = 0.874 (height in cm) – 0.596 (age, years) – 1.016 (fat mass, kg) + 1.638 (lean mass, kg) + 2.461 (reps x sets x load x 10^-3) – 110.742.

Bottom line: in a session that took 42-56 minutes, men burned about 161+/-66 calories and women burned 88+/-39.  There was an upside: men and women burned similar calories per unit body weight.                                                                                                                               

MSSE July 2019

Tid Bits