Technology practice questions.

A futsal coach wants to record the distance covered by players during matches in a sports hall. Which limitation makes a satellite-based GPS unit unsuitable here?

• Satellite signals do not reach indoors
• The unit records heart rate instead of position
• The unit samples position only once per match
• The unit is too heavy to wear

Answer: Satellite signals do not reach indoors

Satellite positioning needs an unobstructed line of sight to several satellites and a roof blocks it, so indoor sports are monitored with local positioning systems or camera tracking instead. A unit that still reports a position under a roof is working from a degraded fix, so its distance and speed values cannot be trusted.

A middle-distance runner wears a chest strap monitor during an interval session. Which signal does the strap detect?

• Pressure waves in the radial artery
• Changes in light absorption at the skin surface
• The electrical activity of the heart
• Movement of the chest wall during breathing

Answer: The electrical activity of the heart

The strap picks up the electrical depolarisation of the heart, in effect a single-lead electrocardiogram, which is why it stays accurate while the athlete is running hard. An optical sensor instead measures light absorbed by pulsing blood in the skin.

A netball player lands from a rebound onto a force platform set into the floor. Which variable does the platform record directly?

• The vertical ground reaction force over time
• The angle of the knee joint at contact
• The electrical activity of the calf muscles
• The velocity of the centre of mass

Answer: The vertical ground reaction force over time

A force platform measures force against time; velocity, displacement and power are calculated afterwards by integrating that force record with the athlete's body mass. Joint angles require video or motion capture and muscle activity requires electromyography.

Surface electrodes are placed over the vastus lateralis of a cyclist during a sprint. What does the resulting electromyography trace show?

• The force produced by the muscle in newtons
• The electrical activity of the muscle
• Muscle fibre length
• The rate of oxygen uptake in the muscle

Answer: The electrical activity of the muscle

Surface electromyography detects the summed action potentials arriving at the fibres beneath the electrodes, so it shows when a muscle is active and roughly how strongly it is being driven. It does not measure force, because force also depends on muscle length, shortening velocity and joint angle.

A biomechanist films a long jump take-off from the side for two-dimensional analysis. What must appear in the field of view so that image measurements can be converted into metres?

• A stopwatch visible in the corner of the frame
• A second camera positioned behind the board
• A heart rate display
• A rod of known length in the same plane

Answer: A rod of known length in the same plane

Digitising software works in pixels, so a scaling object of known length filmed in the plane of the movement is needed to convert those pixels into real distances. If the object lies outside the movement plane the scale factor applied to the athlete is wrong.

A data logger stores heart rate once every 60 s during a two-hour mountain-bike ride. Which consequence does this sampling interval have?

• The mean heart rate cannot be calculated at all
• Brief peaks that occur between recordings are missed
• All recorded values are systematically too high
• The logger reports beats per hour instead of per minute

Answer: Brief peaks that occur between recordings are missed

A long sampling interval smooths the record, so short surges on the climbs fall between samples and both the peak values and the time spent at high intensity are underestimated. A shorter interval captures them at the cost of a much larger data file.