We compared backward with forward running to test the idea that the application of ground force to support the weight of the body determines the energetic cost of running. We hypothesized that higher metabolic rates during backward versus forward running would be directly related to greater rates of ground force application and the volume of muscle activated to apply support forces to the ground. Four trained males ran backward and forward under steady-state conditions at eight treadmill speeds from 1.75 to 3.50 m s(−)(1). Rates of oxygen uptake were measured to determine metabolic rates, and inverse periods of foot-ground contact (1/t(c)) were measured to estimate rates of ground force application. As expected, at all eight speeds, both metabolic rates and estimated rates of ground force application were greater for backward than for forward running. At the five slowest speeds, the differences in rates of ground force application were directly proportional to the differences in metabolic rates between modes (paired t-test, P<0.05), but at the three highest speeds, small but significant differences in proportionality were present in this relationship. At one of these three higher speeds (3.0 m s(−)(1)), additional measurements to estimate muscle volumes were made using a non-invasive force plate/video technique. These measurements indicated that the volume of muscle active per unit of force applied to the ground was 10+/−3 % greater when running backward than forward at this speed. The product of rates of ground force application and estimated muscle volumes predicted a difference in metabolic rate that was indistinguishable from the difference we measured (34+/−6 % versus 35+/−6 %; means +/− s.e.m., N=4). We conclude that metabolic rates during running are determined by rates of ground force application and the volume of muscle activated to apply support forces to the ground.

REFERENCES

Armstrong
R. B.
,
Delp
M. D.
,
Goljan
E. F.
,
Laughlin
M. H.
(
1987
).
Distribution of blood flow in muscles of miniature swine during exercise.
J. Appl. Physiol
62
,
1285
–.
Barany
M.
(
1967
).
ATPase activity of myosin correlated with speed of muscle shortening.
J. Gen. Physiol
50
,
197
–.
Bellizzi
M. J.
,
King
K. A. D.
,
Cushman
S. K.
,
Weyand
P. G.
(
1998
).
Does the application of ground force set the energetic cost of cross-country skiing?.
J. Appl. Physiol
85
,
1736
–.
Biewener
A. A.
(
1990
).
Biomechanics of mammalian terrestrial locomotion.
Science
250
,
1097
–.
Biewener
A. A.
,
Konieczynski
D. D.
,
Baudinette
R. V.
(
1998
).
In vivo muscle force—length behavior during steady-speed hopping in tammar wallabies.
J. Exp. Biol
201
,
1681
–.
Cavagna
G. A.
,
Heglund
N. C.
,
Taylor
C. R.
(
1977
).
Mechanical work in terrestrial locomotion: two basic mechanisms for minimizing energy expenditure.
Am. J. Physiol
233
,
243
–.
Cavagna
G. A.
,
Sabiene
F. P.
,
Margaria
R.
(
1964
).
Mechanical work in running.
J. Appl. Physiol
19
,
249
–.
Cogger
D. C.
,
Hoyt
D. F.
,
Wickler
S. A.
,
Magana
S. A.
(
2000
).
Reproducibilty of skeletal muscle sonomicrometry in the horse.
Physiologist
43
,
28
–.
Fedak
M. A.
,
Rome
L.
,
Seeherman
H. J.
(
1981
).
One-step N2-dilution technique for calibrating open-circuit V Omeasuring systems.
J. Appl. Physiol
51
,
772
–.
Flynn
T. W.
,
Connerty
S. M.
,
Smutok
M. A.
,
Zeballos
R. J.
,
Weisman
I.
(
1994
).
Comparison of cardiopulmonary responses to forward and backward walking and running.
Med. Sci. Sports Exerc
26
,
89
–.
Flynn
T. W.
,
Sousas-Little
R. W.
(
1995
).
Patellofemoral joint compressive forces in forward and backward running.
J. Orth. Sports Phys. Therapy
21
,
277
–.
Glasheen
J. W.
,
McMahon
T. A.
(
1995
).
Arms are different from legs: mechanics and energetics of human hand-running.
J. Appl. Physiol
78
,
1280
–.
Heglund
N. C.
,
Fedak
M. A.
,
Taylor
C. R.
,
Cavagna
G. A.
(
1982
).
Energetics and mechanics of terrestrial locomotion. IV. Total mechanical energy changes as a function of speeds and body size in birds and mammals.
J. Exp. Biol
79
,
57
–.
Hill
A. V.
(
1950
).
The dimensions of animals and their muscular dynamics.
Sci. Prog
38
,
209
–.
Hoyt
R. W.
,
Kanpik
J. J.
,
Lanza
J. F.
,
Jones
B. H.
,
Staab
J. S.
(
1994
).
Ambulatory foot contact monitor to estimate metabolic cost of human locomotion.
J. Appl. Physiol
76
,
1818
–.
Kaneko
M.
(
1990
).
Mechanics and energetics in running with special reference to efficiency.
J. Biomech
23
,
57
–.
Kram
R.
,
Powell
A. J.
(
1989
).
A treadmill-mounted force platform.
J. Appl. Physiol
67
,
1692
–.
Kram
R.
,
Taylor
C. R.
(
1990
).
The energetics of running: a new perspective.
Nature
346
,
2265
–.
Lejeune
T. M.
,
Willems
P. A.
,
Heglund
N. C.
(
1998
).
Mechanics and enrgetics of human locomotion on sand.
J. Exp. Biol
201
,
2071
–.
McMahon
T. A. G.
,
Valiant
G.
,
Frederick
E. C.
(
1987
).
Groucho running.
J. Appl. Physiol
62
,
2326
–.
Minetti
A. E.
,
Alexander
R. McN
(
1997
).
A theory of metabolic costs for bipedal gaits.
J. Theor. Biol
186
,
467
–.
Minetti
A. E.
,
Ardigo
L. P.
,
Saibene
F.
(
1994
).
MechanicalS. WRIGHTANDP. G. WEYAND1815 Energetics and mechanics of human running determinants of the minimum energy cost of gradient running in humans.
J. Exp. Biol
195
,
211
–.
Roberts
T. J.
,
Chen
M. S.
,
Taylor
C. R.
(
1998
).
Energetics of bipedal running. II. Limb design and running mechanics.
J. Exp. Biol
201
,
2753
–.
Roberts
T. J.
,
Kram
R.
,
Weyand
P. G.
,
Taylor
C. R.
(
1998
).
Energetics of bipedal running. I. Metabolic cost of generating force.
J. Exp. Biol
201
,
2745
–.
Roberts
T. J.
,
Marsh
R. L.
,
Weyand
P. G.
,
Taylor
C. R.
(
1997
).
Muscular force in running turkeys: the economy of minimizing work.
Science
275
,
1113
–.
Steudel
K.
(
1990
).
The work and energetic cost of locomotion. I. The effects of limb mass distribution in quadrupeds.
J. Exp. Biol
154
,
273
–.
Taylor
C. R.
,
Schmidt-Nielsen
K.
,
Raab
J. L.
(
1970
).
Scaling of energetic cost of running to body size in mammals.
Am. J. Physiol
219
,
1104
–.
van Ingen Schenau
G.
(
1998
).
Positive work and its efficiency are at their dead-end: comments on a recent discussion.
J. Biomech
31
,
195
–.
Willems
P. A.
,
Cavagna
G. A.
,
Heglund
N. C.
(
1995
).
External, internal and total work in human locomotion.
J. Exp. Biol
198
,
379
–.
Williams
K.
,
Cavanaugh
P. R.
(
1987
).
Relationship between distance running mechanics, running economy and performance.
J. Appl. Physiol
63
,
1236
–.
This content is only available via PDF.