exercise physiology

1. ENERGY EXPENDITURE
DURING JOGGING &
RUNNING
AAKANKSHA BAJPAI
MPT

2.  Terrain, weather, training goals, and the performer’s
fitness level influence the speed of running. Two ways
quantify running energy expenditure:
1) During performance of the actual activity.
2) On a treadmill in the laboratory, with precise control
over running speed and grade.

3.  Jogging and running represent qualitative terms related
to speed of locomotion. This difference relates largely to
the relative aerobic energy demands required in raising
and lowering the body’s center of gravity and
accelerating and decelerating the limbs during the run.
 At identical running speeds, a trained distance runner
moves at a lower percentage of aerobic capacity than an
untrained runner, even though the oxygen uptake during
the run may be similar for both.

4.  The demarcation between jogging and running
depends on the participant’s fitness; a jog for one
person represents a run for another.
 Independent of fitness, it becomes more
economical from a energy standpoint to discontinue
walking and begin to jog or run at speeds greater
than about 6.5 km/hr(4.0 mph).

5. RUNNING ECONOMY
 Oxygen uptake relates linearly to running speed;
thus, the same total caloric cost results when
running a given distance at a steady-rate oxygen
uptake at a fast or slow pace.
 In simple terms, if one runs a mile at a 10-mph
pace (16.1 km/hr), it requires about twice as much
energy per minute as a 5-mph pace (8 km/hr). The
runner finishes the mile in 6 minutes, but running at
the slower speed requires twice the time, or 12
minutes. Consequently, the net energy cost for the
mile remains about the same regardless of the
pace ( 10%).

6.  For horizontal running, the net energy cost (i.e.,
excluding the resting requirement) per kilogram of
body mass per kilometer traveled averages
approximately 1 kCal or 1 kCal.kg-1.km-1)
 For an individual who weighs 78 kg, the net energy
requirement for running 1 km equals about 78 kCal,
regardless of running speed.
 Expressed as oxygen uptake, this amounts to 15.6 L
of oxygen consumed per kilometer (1 LO2 = 5 kCal;
5.0 * 15.6).

7. ENERGY COST OF RUNNING
 The energy cost per mile increases proportionately
with the runner’s body mass.
 This observation certainly supports the role of
weight-bearing exercise as a caloric stress for
overweight individuals who wish to increase energy
expenditure for weight loss.

8. STRIDE LENGTH AND STRIDE FREQUENCY
EFFECTS ON RUNNING SPEED
 Running speed can increase in three ways:
1) Increase the number of steps each minute (stride
frequency)
2) Increase the distance between steps (stride
length)
3) Increase stride length and stride frequency

9. OPTIMUM STRIDE LENGTH
 An optimum combination of stride length and frequency
exists for running at a particular speed.
 The optimum combination depends largely on the
person’s “style” of running and cannot be determined
from objective body measurements.
 Running speed chosen by the person incorporates the
most economical stride length. Lengthening the stride
above the optimum increases oxygen uptake more
than a shorter-than-optimum stride length.
 Urging a runner who shows signs of fatigue to
“lengthen stride” to maintain speed proves
counterproductive for exercise economy.

10. EFFECTS OF AIR RESISTANCE
 Anyone who has run into a strong headwind knows
it requires more energy to maintain a given pace
compared with running in calm weather or with the
wind at one’s back.
 Three factors influence how air resistance affects
energy cost of running:
1) Air density
2) Runner’s projected surface area
3) Square of headwind velocity

11.  Depending on running speed, overcoming air
resistance accounts for 3% to 9% of the total
energy requirement of running in calm weather.
 Wind tunnel tests show that running performance
increases by wearing from-fitting clothing; even
shaving body hair improves aerodynamics and
reduces wind resistance effects by up to 6%.
 At altitude, wind velocity affects energy expenditure
less than at sea level because of reduced air
density at higher elevations.

12. DRAFTING
 Athletes use “drafting” by following directly behind a
competitor to counter the negative effects of air
resistance and headwind on energy cost.
 For example, running 1 m behind another runner at
a speed of 21.6 km/hr (13.4 mph) decreases the
total energy expenditure by about 7%. Drafting at
this speed could save about 1 second for each 400
m covered during a race.

13. TREADMILL VERSUS TRACK RUNNING
 No meaningful differences occurred in aerobic
requirements of submaximal running (up to 17.2
km/hr) on the treadmill or track or between the
VO2max measured in both exercise forms under
similar environmental conditions.
 At the faster running speeds of endurance
competition, air resistance could negatively impact
outdoor running performance and oxygen cost may
exceed that of “stationary” treadmill running at the
same speed.