Exercise Economy / Efficiency

Exercise economy (sometimes referred to as the economy of motion, or efficiency) refers to the volume of oxygen (ml.kg.min-1) required to move at a given speed, power output, or work rate. It is a powerful predictor of endurance exercise performance in several endurance sports (cycling, swimming, running, etc). And can explain differences in endurance exercise performance between individuals.

The economy of motion is influenced by several factors including neuro-muscular co-ordination, % type I muscle fibers, elastic energy storage, joint stability and flexibility.

Factors That Influence Exercise Economy

#1 Neuromuscular coordination

Every muscular contraction in the human body involves a coordinated contraction of individual muscles, groups of muscles, and muscle fibres. This happens on an intra-muscular level (coordination of muscle fibres and motor units) and inter-muscular level (between groups of working muscles). This is referred to as neuromuscular coordination.

Through specialised training, we can achieve greater levels of coordination between muscle fibres, muscles, and groups of muscles. This improves exercise economy and reduces the energy cost of exercise.

#2 Percentage of Type I muscle fibres

Research has shown that the ratio of type I and type II muscle fibres affects exercise economy (Mogensen et al., 2006; Horowitz et al., 1993; Coyle 1992;).

How muscle fibres affect exercise economy:

Type I muscle fibers have a greater level of efficiency than type II muscle fibres.

We can further divide type II fibres into Type IIa (fast twitch oxidative) and Type IIb (fast twitch glycolytic) muscle fibres.

Type IIa muscles are less efficient than Type I, but more efficient than Type IIb fibres.

Athletes with a higher proportion of Type I and and IIa muscle fibres, show greater economy than those with a higher ratio of Type II and specifically Type IIb.

Through specialized endurance exercise we can further develop the economy of Type I and IIa muscle fibres. One factor here is a gradual transformation within Type IIa fibres towards the characteristics of slow twitch fibres.

#3 Elastic energy storage

An enhanced elastic energy storage has a positive effect on exercise economy (Sawicki et al., 2009). This is important in dynamic sports such as running, where we convert potential and kinetic energy into elastic energy stored within the tendons and muscles.

Specific training such as max velocity training and plyometrics can improve the ability to store and use this elastic energy.

#4 Joint stability, flexibility and efficiency

Increased joint stability and reduced flexibility can enhance exercise efficiency in dynamic sports, like running. Researchers have found that reduced joint flexibility—particularly in the hip and calf regions—is associated with improved running economy (Jones 2002; Craib et al. 1996; Gleim et al. 1990) and walking economy (Hunter et al., 2008; Gleim et al. 1990). To support this, orthotics—often used to reduce excessive pronation and increase stability—have been found to improve running economy at lower intensities (Burke and Papuga 2012).

Interestingly, the Sit and reach range of motion is negatively associated with running economy (Jones 2002; Brown et al., 2011). And when researchers looked at a gene linked to muscle tendon stiffness, they found that the geneotype was linked with endurance running performance (Brown et al., 2011).

Researchers have also associated greater muscle stiffness and less power with greater running economy (Dumke et al., 2010).

Explanations for the inverse relationship between efficiency and flexibility include:

Improved use of elastic energy (Hunter et al., 2008)
Reduced recruitment of unproductive muscles for stabilization of the joints (Martin and Morgan 1992).

Clearly, excessive flexibility and reduced stability increases the work rate of stabilising muscles. With this in mind, specific exercises that increase stability—strength and core stability exercises—may help to increase stability and improve exercise efficiency.

#5. Symmetry and exercise efficiency

Symmetry is also an important factor.

So, what do we mean by symmetry? We can view symmetry in two ways:

1) We can view symmetry in terms of similar limb length, muscle strength, joint stability and flexibility on the left and right sides of our body.

Or,

2) The ability to apply equal amounts of force on the left and right sides of our body.

Clearly, these are both important.

In terms of sports performance, it’s the ability to apply force equally on both sides of your body that is vital for efficiency. Much like the way wheel alignment is essential for car efficiency, any imbalances will reduce efficiency and increase wear and tear.

This is important in sports, like swimming and running where imbalances can reduce efficiency. In fact, a recent study found that ground contact time imbalances significantly reduced running efficiency.

#6 Genetics and efficiency

There turns out to be a strong genetic influence regarding exercise efficiency. In fact, genetics accounts for up to 20-30% of variation in running economy, among trained runners of similar ability (Morgan and Daniels, 1994).

Genetics also plays a role in how well we respond (adapt) to training. For this reason, some individuals achieve greater improvements in their exercise efficiency.

Exercise Efficiency And Sports Performance

Research has shown that exercise economy is a key factor in endurance exercise performance (Hausswirth and Lehénaff 2001; Morgan et al., 1989; Williams and Cavanagh 1987; Scrimgeour et al., 1986; Conley and Krahenbuhl 1980;).

It can help to explain differences in endurance performance between individuals. There appears to be wide variation between individuals, with 30-40% variation in running economy between individual runners (Joyner, 1991; Conley & Krahenbuhl, 1980; Farrell et al. 1979;) and 20-30% variation in cycling economy between individual cyclists (Coyle, 1995).

As with other performance factors—like the lactate threshold, VO2 max etc—we can improve exercise economy through specialized training. This leads to improved endurance exercise performance (Coyle F, 2005; Jones, 1998; Toussaint and Hollander 1994 Krahenbuhl et al., 1989; Conley et al., 1984;).

Running economy

Several studies have established that running economy accounts for a significant amount of the variation in long distance running performance. And many researchers consider this vital for success in distance running events.

Researchers have discovered it to be highly predictive of 10km running performance (Williams and Cavanagh 1987; Conley and Krahenbuhl 1980;) and Marathon performance (Sjödin B, and Svedenhag J. 1985). However, research into the importance of running economy over middle distance events is less conclusive.

Performance during 800m running was not predicted by running economy (Craig and Morgan 1998). It was moderately predictive of 3km race performance (Grant et al., 1997).

Researchers looking at 5km running performance have observed mixed results:

One study found running economy had only a modest effect on 5km running performance (Ramsbottom et al., 1987), while another found it highly predictive of 5k running performance (Paavolainen et al., 1999).

The research shows that running economy becomes progressively important as race distance increases. This is not surprising given that as race distance increases we run at smaller percentages of VO2 max.

During middle distance events, factors like the VO2 max and vVO2max are increasingly important. However, running economy is very important during long distance events.

The VO2-speed relationship running

An important consideration is the relationship between VO2 and speed. As exercise intensity increases, the oxygen cost rises linearly, however the rate of increase (gradient) varies between individuals.

This is important when assessing running economy. Athletes with a high rate of increase in oxygen cost have greater efficiency at slower speeds (e.g. marathon pace), whereas athletes with a low rate of increase tend to have better economy over faster speeds, such as 3k-5k pace (Daniels and Daniels, 1992).

This can explain why some athletes are more suited to middle distance events, while others are better suited to longer events.

One point to note: research suggests that the VO2-speed relationship changes at speeds above the lactate threshold—with a greater than 50% reduction in the slope of the VO2-velocity relationship at intensities above the lactate threshold (Bickham et al., 2004). This suggests that we should assess running economy at race pace.

Endurance cycling efficiency

Exercise efficiency also turns out to be an important factor in cycling (Leirdal and Ettema 2011; Joyner and Coyle 2008; Olds et al., 1995;). While exercise economy in running looks at the relationship between running speed and oxygen uptake. In cycling, we look at the relationship between work rate (power) and oxygen uptake.

The most common approach is to look at gross efficiency, which looks at the ratio of work accomplished to the amount of energy expended. Essentially, this measures the power produced for a given oxygen consumption and energy expenditure.

Cyclists with better efficiency can produce higher power at a given oxygen consumption. For this reason, it is deemed vital for success in endurance cycling events.

Efficiency and swimming

Since technique is vital for success in swimming events, it shouldn’t be a surprise that efficiency is vital (Fernandes et al., 2006; Kjendlie et al., 2004; Toussaint and Hollander 1994; Toussaint and Beek 1992).

Research in swimming suggests that improvements in propelling efficiency have a more beneficial effect on swimming performance than a proportional increase in either aerobic or anaerobic power (Toussaint and Hollander 1994). Research also suggests that the age associated declines in swimming performance may be because of an increase in the energy cost of swimming (Zamparro et al., 2012).

Exercise Economy vs VO2 max

The positive correlation between exercise economy and exercise performance has led many researchers to view economy as one of the most important factors in endurance performance.

That said, it’s necessary to consider that a great level of efficiency cannot make up for a low VO2 max and vice versa. Interestingly, research suggests that athletes with greater exercise economy tend to have a lower VO2max (Sawyer et al., 2010; Lucia et al., 2002; Pate et al., 1992), lower oxidative capacity within the muscle (Hunter et al., 2005) and greater weight (Pate et al., 1992).

This indicates that a better exercise economy may allow some athletes to compete successfully in endurance sports where they would not otherwise be physiologically suited. For instance, it can compensate for a reduced VO2max, higher weight, lower oxidative capacity within the muscle—all factors normally considered essential for success in endurance sports.

How To Improve Exercise Economy

There are several approaches that can improve exercise economy. These include:

Plyometrics and strength training
Lactate threshold
High intensity training
Sprint Intervals
Increased training volume

Plyometrics and strength training

Resistance training (especially heavy resistance training) and or explosive strength training has proven to significantly improve exercise economy/efficiency in several endurance sports. These include: middle to long distance running (Cheng et al., 2012; Mikkola et al., 2011; Taipale et al., 2010; Guglielmo et al., 2009; Støren et al., 2008; Yamamoto et al., 2008; Spurrs et al., 2003; Paavolainen et al., 1999b), cycling (Louis et al., 2012; Rønnestad BR, et al., 2012; Sunde et al., 2010; Paton and Hopkins 2005), swimming (Girold et al., 2012 & 2006; Konstantaki et al., 2008) and cross-country skiing (Hoff et al., 2002; Hoff et al., 1999;).

Heavy resistance training and explosive strength training has proved effective at improving running economy, with improvements of 6-8% reported in some short-term studies (Guglielmo et al., 2009; Paavolainen et al., 1999b). Similarly, explosive and heavy resistance training has proved effective at improving cycling efficiency (Louis et al., 2012; Sunde et al., 2010).

Interestingly, research looking at the benefits of resistance training (10 sets of 10 knee extensions at 70% repetition maximum) in master endurance athletes found that it alleviated the age-related reductions in strength and efficiency (Louis et al., 2012).

Resistance training has again been beneficial for increasing efficiency in swimmers (Girold et al., 2006 & 2012; Konstantaki et al., 2008) although it requires more swim specific forms of resistance training.

Exercise economy and training intensity

Training intensity appears to play a key role in the development of an improved economy of motion.

One factor appears to be that improvements occur at the speeds used during training.

Researchers noticed that running economy improved at the speed used during training (Beneke and Hütler 2005). Therefore, it’s recommended that athletes include sufficient amounts of training at speeds, or intensities used in competition.

High Intensity Intervals

Including training at intensities around or above the lactate threshold is also important. Researchers have found that cycling efficiency can be enhanced through high intensity training (Hopker et al., 2010) and appears to be linked to the amount of training spent above OBLA (onset of blood lactate accumulation); and the total volume of training (Hopker et al., 2009).

Research in runners found that exercise at 95 or 100% of vVO2 max (~3km-10km race pace), twice per week, significantly improved running economy (Denadai et al., 2006).

Research indicates that the length of the training interval may also be an important factor.

In one study, researchers (Franch et al., 1998) compared the effects of three different training types. They performed these three times per week for 20-30minutes. Researchers discovered that intensive training (tempo training/lactate threshold training), and long interval training, was more effective at improving running economy than short interval training (~3% vs <1% improvement).

Sprint Intervals

More recently, research has clearly showed that sprint training improves running economy by around 3-6%. Taken together, this tells us that economy can be improved using a range of intensities from lactate threshold to sprint (maximal) intensity, with sprint training producing the biggest effects.

Exercise economy and training volume

Training volume appears to be a key factor regarding exercise economy (Hopker et al., 2009; Scrimgeour et al., 1986).

When researchers looked at the effects of training volume, prior to competition, they found that the runners with a training volume of more than 100km/week had the greatest running economy (Scrimgeour et al., 1986).

The most crucial factor regarding training volume and exercise economy, appears to be the amount of training performed at race pace. For this reason, athletes should ensure that they complete an adequate amount of training at or near race pace/intensity.

For athletes competing in events of 30-60minutes duration, this could involve lactate threshold training performed at or just below the lactate threshold.

It is important to remember that increasing training volume is expected to lead more gradual improvements in exercise economy. For this reason, achieving consistent increases in training volume, and the volume of race pace training, should form part of a longer-term strategy.

Stretching and exercise efficiency

Decreased flexibility is associated with improved running economy, and some suggest that stretching may negatively impact exercise economy. However, this idea is controversial. While there is clear evidence that decreased flexibility is linked to improved economy, there is conflicting research regarding the effects of stretching and running economy.

Research in this area, has found that running economy doesn’t appear to be negatively influenced by stretching (Mojock et al., 2011; Hayes and Walker 2007; Nelson et al., 2001). However, research looking at the effects of stretching and cycling have found reduced cycling efficiency following stretching (Esposito and Limonta 2011; Wolfe et al 2011).

Researchers have found static stretching reduces cycling efficiency (Esposito and Limonta 2011; Wolfe et al 2011). Because of this, researchers recommended that highly trained endurance cyclists should avoid static stretching prior to moderate intensity cycling (Wolfe et al 2011).

Training experience

Training experience may play a crucial role, with improvements occurring gradually over many years. While research is limited, two case studies have revealed improved running economy (14% improved running economy over 5 years) and cycling efficiency (8% improved cycling efficiency over 7 years) in elite athletes (Jones 2006; Coyle 2005;).

Specific considerations for cycling

Research has demonstrated that the technical aspects of bike setup and pedalling efficiency can have a significant effect on cycling efficiency.

Pedalling efficiency appears to play a significant role, particularly during endurance cycling. This is affected by the ability to generate a constant force throughout the pedal stroke, and the cadence.

One area that has received a lot of interest is cadence. Currently, research is not conclusive as to the most efficient pedal rate (Ettema and Lorås, 2009). Some research has found that triathletes and cyclists are more economical when cycling at 60rpm, rather than faster pedal rates (Jacobs et al., 2012; Sacchetti et al., 2010). Others have identified higher pedal rates (80-90rpm) to be more efficient (Dantas et al., 2009; Foss and Hallén, 2004).

Research indicates that lower pedalling rates appear to be more economical amongst older (~65years) cyclists (Sacchetti et al., 2010).

In terms of training, research indicates that low-cadence interval training (70rpm) may be more useful than high cadence interval training (110-120rpm) for improving measures of cycling performance, including exercise economy (Paton et al., 2009).

Other factors that appear to influence cycling efficiency include the pedalling technique (Canon et al., 2007; Zameziati et al., 2012) and saddle height (Peveler and Green 2011). Research looking at the effect of saddle height on cycling economy, found that oxygen consumption was significantly lower when saddle height was set up so there was a 25° knee angle.

Exercise Economy Summary:

Exercise economy is influenced by several factors including neuromuscular co-ordination, % type I muscle fibres, elastic energy storage, joint stability and genetics.
Endurance race performance is strongly linked to exercise economy in sports like running, swimming and cycling.
It plays a greater role with increasing race duration.
Improvements occur following heavy resistance and plyometric training, and we should view this as an essential training method for endurance athletes.
High-intensity intervals and sprint training are very effective for improving economy.
Improvements occur at the speed, or intensities, used during training. Therefore, it’s essential that athletes include adequate training at these intensities.
Other training factors that influence exercise economy include the volume and the intensity of training, and the amount of training performed above OBLA (onset of blood lactate accumulation).
There is evidence that stretching may negatively affect cycling efficiency; however, research in runners has not found a link between stretching and reduced economy.
Increasing training volume can bring about slow and progressive improvements over several years. For this reason, carefully controlling training intensity and volume, to avoid periods of interrupted training—injuries, illness, over-training, etc—is essential for long-term training progression.
Cycling has several specific factors that may affect efficiency including cadence, the cadence used during training, saddle height, and pedalling efficiency.

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