Reports by Andrew Hamilton

Torso stabilisation increases cycling efficiency

In cycling exercise studies that have been used to evaluate muscle metabolism and energy output, it has always been assumed that any metabolic changes are due to the muscles actually involved in cycling. But new research conducted by US scientists at the University of Utah has thrown this assumption into doubt.

The goal of this study was to determine whether a torso stabilisation device would reduce the metabolic cost of producing cycling power – ie increase cycling efficiency and lower energy expenditure for the same cycling power output.

Nine male cyclists cycled on a Velotron cycle ergometer at power outputs that produced 50, 75, and 100% of their ventilatory thresholds (the exercise intensity that produces a sudden jump in breathing rate). Three different pedal cadences were used: 40rpm, 60rpm and 80rpm. Each cyclist was tested with and without torso stabilisation (a device to limit movement in the torso when pedalling).

The metabolic costs of these different intensities and pedalling cadences measured with and without the stabilisation device showed that not only did torso stabilisation reduce the metabolic cost of producing sub-maximal cycling power (ie increase cycling efficiency) but that this reduction was also related to pedalling cadence. The overall reduction in metabolic cost was around 1%, with the greatest reductions at lower pedalling rates where pedalling force was greatest (-1.6% at 40rpm, -1.2% at 60rpm, -0.2% at 80rpm).

The researchers concluded that ‘muscular contractions associated with torso stabilisation elicit significant metabolic costs, which tend to be greatest at low pedalling rates’. The implications of this study are potentially significant for cyclists. Not only does high cadence pedalling appear to increase efficiency by reducing the amount of energy required to stabilise the upper body when cycling, but there’s also the possibility that cyclists with efficient torso stabilising muscles (ie greater core stability) may have an energetic advantage over those with weak stabilising muscles.

Can J Appl Physiol Aug 2005; 30(4):433-41

More evidence for the benefits of carbohydrate feeding during cycling

There can’t be many sportsmen or women who are not aware of the tremendous importance of dietary carbohydrate for sports performance. But while much of the emphasis has been on the replenishment of carbohydrate after training or competition, new evidence continues to emerge indicating that carbohydrate feeding during exercise may offer significant benefits.

In a Dutch study on cyclists, the scientists set out to investigate what impact the feeding of carbohydrate during a 75-minute training ride at 80% VO2max had on body stores of carbohydrate and also on protein oxidation.

Five highly trained cyclists took part in two trials; in one trial they rode while ingesting 125 grams of carbon-13 (C-13) radio-labelled glucose, while in the second, no C-13 glucose was administered. C-13 glucose acts a tracer of glucose metabolism in the body, allowing scientists to identify the source of any oxidised glucose. By analysing the amount of C-13 CO2 exhaled, the scientists were able to determine what proportion of the energy used during the trial was provided by ingested C-13 glucose, and what proportion was from stored muscle carbohydrate (glycogen). They also measured urine and sweat metabolites to see how much protein was being oxidised during exercise.

Unsurprisingly perhaps, they found that glucose feeding reduced liver glycogen usage by 12% and muscle glycogen usage by 16%. The impact on protein utilisation for energy, however, was more profound; glucose feeding resulted in a two-thirds drop in protein oxidation.

These results add to the growing body of evidence that the practice of carbohydrate feeding during training offers significant benefits to endurance athletes such as cyclists, especially
given that these cyclists were not glycogen depleted before the trials.

Not only can it reduce spare endogenous stores of muscle glycogen, it also appears dramatically to reduce the loss of muscle tissue that occurs via protein oxidation, something that may be particularly useful for endurance athletes who struggle to maintain lean muscle mass during periods of high-volume training or competition.
Int J Sport Nutr Exerc Metab Aug 2005;15(4):350-65

Dehydration affects lactate accumulation in cyclists

New research carried out by Belgian scientists suggests that exercise-induced dehydration can significantly affect the rate of fatigue-inducing lactate accumulation during cycling. Nine triathletes completed two test sessions in random order. These sessions consisted of:

- Hydration condition – two graded cycling tests to exhaustion (pre-test and post-test) interspersed by a two-hour endurance exercise bout during which 1.35 litres of fluid per hour was administered to keep the subjects hydrated, plus carbohydrates to supply energy;

- Dehydration condition – exactly as above, but with no fluid administered during the endurance bout.

The researchers were particularly interested to see how dehydration affected the power/lactate curve – ie whether the dehydration would produce lactate accumulation at lower power outputs or heart rates.

Unsurprisingly, the dehydration condition produced a loss of around 2kg of body weight compared to the hydration condition; however, this did not appear to affect the heart rates at which lactate threshold was reached. The relationship between power outputs and lactate threshold told a different story, with a drop of around 12% in power output for the same level of blood lactate – or to put it another way, a higher blood lactate level for the same power output.

So what does this mean for cyclists? According to the scientists, when dehydration is a potential problem, cyclists who are carrying out structured training based on blood lactate levels should use heart rates to monitor exercise intensity and not power outputs. This is because while dehydration doesn’t appear to affect the relationship between heart rate and blood lactate it does affect the blood lactate/power output relationship.
Int J Sports Med Dec 2005; 26(10):854-8

The risks of iron overload in cyclists
Given the essential role of iron in maintaining blood haemoglobin levels, and therefore oxygen-carrying capacity, it’s hardly surprising that iron supplementation is a common practice in endurance athletes such as cyclists. But according to new research by Italian scientists, many professional cyclists may be getting too much of a good thing, particularly as (unlike many nutrients) excessive intakes of iron are not easily or rapidly excreted, and too much stored iron in the body is known to be toxic.

The study examined the levels of serum ferritin, an iron-containing protein found in blood that provides a good indication of total body iron stores, in the follow groups:

- 60 male healthy sedentary controls;
- 80 amateur road cyclists;
- 42 male professional cross-country skiers;
- 88 male professional road cyclists.

The results showed that the concentration of serum ferritin in healthy controls averaged 112ng/ml, whereas that of the amateur cyclists and cross-country skiers was 127 and 183ng/ml respectively. Meanwhile, serum ferritin levels in the pro cyclists averaged 218ng/ml – concentrations that are around two to three times higher than those of matched sedentary individuals and amateur athletes.

The researchers concluded that both the cross-country skiers and the pro cyclists had serum ferritin levels exceeding the threshold for the diagnosis of biochemical iron overload and which could put them at potential metabolic risk. The message seems clear: cyclists who use routine iron supplementation need to keep an eye on their iron status with regular testing and shouldn’t supplement indiscriminately.
Clin J Sport Med 2005; 15(5):356-358