Cycling efficiency (efficiently):what does it really mean?

Andrew R. Coggan, Ph.D.

Cardiovascular Imaging Laboratory

Washington University School of Medicine

St. Louis, MO 63110

Cycling efficiency

• What is it?• How do you measure it?• Why is it important?• What determines it?• How do you train it?

Cycling efficiency –what is it?

Definition• The same as in other scientific fields, e.g.,

physics: energy out/energy in x 100%

Related concepts• Net efficiency, delta efficiency, economy

Cycling efficiency –how do you measure it?

• Only one way to do so: → by using a metabolic chamber or cart to

quantify energy liberation via direct or indirect calorimetry while simultaneously measuring power output using a cycle ergometer (or bicycle-mounted power meter).

Direct versus indirect calorimetry

Sample calculation of efficiency

• Power (energy out) = 159 W (159 J/s)

• VO2 = 2.16 L/min

• RER = 0.82• Energy in = 2.16 L/min x 4.825 kCal/L x 4184

J/kCal x 1 min/60 s = 728 J/s• Efficiency = energy out/energy in x 100%• Efficiency = 159 J/s x 1/728 J/s x 100%

= 21.8%

Effect of absolute power output on gross efficiency

Cycling efficiency –why is it important?

• Cycling efficiency represents the link between ATP turnover and external power output.

• Thus, for a given metabolic rate a more efficient individual will be able to produce more power, and/or will be able to produce a given power output at a lower metabolic rate (= less physiological strain).

Effect of cycling economy on performance (“hour power”)

Horowitz, Sidossis, and Coyle. Int J Sports Med 1994; 15:152-157

Variations in efficiency in world class cyclists

Lucia et al. Med Sci Sports Exerc 2002; 34:2079-2084

Cycling efficiency –what determines it?

Biomechanical factors• Saddle height• Cadence (speed of muscle shortening)• Not crank length• Not fore-aft position of foot• Not pattern of force application

Biochemical factors• Muscle fiber type• UCP3• SERCA1/SERCA 2

Biomechanical factors

Effect of saddle height on efficiency

Price and Donne J Sports Sci 1997; 15:395-402

Effect of cadence on economy

Hagberg et al. J Appl Physiol 1981; 51:447-451

Effect of crank length on efficiency

McDaniel et al. J Appl Physiol 2002; 93:823-828

Effect of foot position on economy

Sickle and Hull J Biomech 2007; 40:1262-1267

The classic “clock diagram” of pedaling forces

Evidence that increasing mechanical effectiveness does not improve

cycling efficiency• Theoretical considerations

– Role of uniarticular and biarticular muscles (Kautz and Neptune Exerc Sports Sci Rev 2002; 30:159-165)

• Cross-sectional observations– On average, pattern of force application very similar in trained

and untrained persons (Morneiux et al. Int J Sports Med 2008; 29:817-822)

Pattern of force application in elite cyclists vs. non-cyclists

Mornieux et al. Int J Sports Med 2008; 29:817-822

• Theoretical considerations– Role of uniarticular and biarticular muscles (Kautz and Neptune

Exerc Sports Sci Rev 2002; 30:159-165)

• Cross-sectional observations– On average, pattern of force application very similar in trained and

untrained persons (Morneiux et al. Int J Sports Med 2008; 29:817-822)

– Inverse relationship between min:max torque and gross (R2 = -0.72; P<0.001) or delta (R2 = -0.76; P<0.001) efficiency (Edwards et al. J Sports Sci 2009; 27:319-325)

– Individuals can be very efficient despite unusual pattern of force application

(continued)

Evidence that increasing mechanical effectiveness does not improve

cycling efficiency

Unusual pattern of force application in a champion cyclist (rider 2)

• Longitudinal (interventional) observations– Removing toe-clips and cleats does not reduce efficiency

(Coyle et al. J Appl Physiol 1988; 64:2622-2630, Ostler et al. J Sports Sci 2008; 26:47-55)

– Training using uncoupled cranks does not improve efficiency (Bohm et al. Eur J Appl Physiol 2008; 103:225-232, Williams et al. Int J Sports Physiol Perform 2009; 4:18-28)

– Acutely altering pedal stroke to be “rounder” reduces efficiency (Korff et al. Med Sci Sports Exerc 2007; 39:991-995)

Evidence that increasing mechanical effectiveness does not improve

cycling efficiency

Effect of pattern of force application on efficiency

Korff et al. Med Sci Sports Exerc 2007; 39:991-995

Effect of pattern of force application on efficiency

Korff et al. Med Sci Sports Exerc 2007; 39:991-995

Biochemical factors

Effect of fiber type on efficiency

Coyle et al. Med Sci Sports Exerc 1992; 24:782-788

Effect of UCP3 on efficiency

Mogensen et al. J Physiol 2006; 571.3:669-681

Effect of training on P:O ratio

Mogensen et al. J Physiol 2006; 571.3:669-681

Effect of training on SERCA1/SERCA2 and efficiency

Majerczak et al. J Physiol Pharmacol 2008; 59:589-602

Cycling efficiency –how do you train it?

Cycling efficiency –can it be trained?

Cross-sectional studies of cycling efficiency

No difference• Boning et al. Int J Sports Med 1984; 5:92-97• Marsh and Martin Med Sci Sports Exerc 1993; 25:1269-1274• Nickleberry and Brooks Med Sci Sports Exerc 1996; 28:1396-1401• Marsh et al. Med Sci Sports Exerc 2000; 32:1630-1634• Mosely et al. Int J Sports Med 2004; 25:374-379

Higher in trained cyclists• Sallet P et al. J Sports Med Fitness 2006; 46:361-365• Hopker et al. Appl Physiol Nutr Metab 2007; 32:1036-1042

Longitudinal studies of cycling efficiency

No change• Roels et al. Med Sci Sports Exerc 2005; 37:138-146

Increases with training• Hintzy et al. Can J Appl Physiol 2005; 30:520-528• Paton and Hopkins J Strength Cond Res 2005; 13:826-830• Majerczak et al. J Physiol Pharmacol 2008; 59:589-602• Sassi et al. Appl Physiol Nutr Metab 2008; 33:735-742• Hopker et al. Med Sci Sports Exerc 2009; 41:912-919• Hopker et al. Appl Physiol Nutr Metab 2010; 35:17-22• Sunde et al. J Strength Cond Res 2010 (in press)

Cycling efficiency –how do you train it?

• “Ordinary” training apparently results in a small, but significant, improvement in cycling efficiency. However, whether efficiency continues to improve over many years or merely oscillates in/out of season around some average value is still uncertain.

(continued)

Cycling efficiency –how do you train it? (con’t)

• Additional improvements might be obtained via “special techniques”, i.e.,:

– High intensity training– Paton and Hopkins J Strength Cond Res 2005; 13:826-830– Hopker et al. Med Sci Sports Exerc 2009; 41:912-919– Hopker et al. Appl Physiol Nutr Metab 2010; 35:17-22

– Training in hypoxia – Gore et al. Acta Physiologica Scandinavica 2001; 173:275-

286– Katayama et al. High Alt Med Biol 2003; 4:291-304

– Resistance training – Sunde et al. J Strength Cond Res 2010 (in press)

Key Points

Cycling efficiency

Is defined as energy out/energy in x 100%;

Can only be determined via use of direct or indirect calorimetry in conjunction with power measurements;

Represents the link between cellular energy “production” and actual performance (i.e., power);

(continued)

Key Points (continued)

Cycling efficiency

Can vary significantly between individuals, even among world class cyclists;

Is apparently determined by both biomechanical (i.e., saddle height, cadence) and biochemical (i.e., fiber type, SERCA activity) factors;

Is either not related to, or is even inversely related to, mechanical effectiveness;

(continued)

Key Points (continued)

Cycling efficiency

Improves as a function of “ordinary” endurance training;

Might be further increased with very prolonged and/or very intense training, and/or as a result of hypoxia or resistance training