Body mass effects on jumping and walking laboratory - semester 2, session 4

Participant's wellbeing in the test:

  • Participant's complete an informed consent form and general health screening form

  • Participant's with current or a history of joint issues are asked not to volunteer

  • Participant's must complete an appropriate exercise warm-up consisting of both jogging on the treadmill and dynamic stretching as well as practicing the jump tests without the additional mass

  • Gloves must be worn when taking capillary blood samples

 

Procedures:

  • Collect two sets of exercise data where the procedures are almost identical, the only difference being that one trial (the intervention trial) will be conducted with the participant carrying an additional mass that is equal to 20% of body mass, whereas no additional mass will be carried in the other trial (the control trial)

  • Both conditions (intervention and control) completed by the same participant

  1. Take a capillary blood sample to determine the resting blood lactate concentration

  2. Familiarise the participant with the treadmill (this should include a full briefing of the health and safety information and the procedures to mount and dismount the treadmill)

  3. Ensure that the participant conducts an appropriate exercise warm-up, this should consist of both jogging and some dynamic stretching that targets the key joints of the lower limb

  4. Conduct 2 x 4-minute stages of treadmill walking at 5 km/h. Intensity will be increased by increasing the treadmill incline from 2% (stage 1) to 8% (stage 2)

  5. During the final minute of each stage collect all the results used in Douglas bag collection

  6. Once completed, bring the treadmill to a stop

  7. Conduct three countermovement jumps and three squat jumps and record the results. The weighted vest should be worn to complete these jumps in the intervention condition

  8. After a short rest period with active recovery (walking on the treadmill, no incline, no additional mass), repeat the treadmill exercise protocol in the other experimental condition and then complete the countermovement and squat jumps

  9. Calculate VO2, fat oxidation, CHO oxidation

 

Changes in VO2 and other physiological responses when walking with increased non-contractile mass:

  • Increased VO2 (oxygen uptake) as more mass requires greater muscular force, greater ground reaction forces, and more mechanical work during walking  = increases metabolic demand. The energetic cost of locomotion rises approximately in proportion to added mass

  • Increased energy expenditure. Because oxygen consumption rises, caloric expenditure also increases. Energy demand is higher due to greater limb acceleration/deceleration, increased stabilisation demands, and greater vertical work against gravity

  • Increased heart rate. Cardiovascular demand increases to deliver more oxygen to working muscles, thus, heart rate rises at a given walking speed

  • Increased ventilation because oxygen demand rises and more CO2 is produced which leads to higher breathing frequency and greater minute ventilation

  • Increased muscle activation as more muscle force is needed to support body weight, absorb impact, and propel the body forward

  • Altered gait mechanics by reducing stride length, increasing stance time, reducing walking speed, or altering joint kinematics = may improve stability or reduce energetic cost

  • Increased ground reaction forces as additional non-contractile mass increases vertical loading, joint compressive forces and impact forces which raises mechanical stress on knees, hips, and ankles

  • Reduced locomotion economy. Walking economy worsens because more energy is required per unit distance

  • Contractile mass (muscle) can contribute force production, however, non-contractile mass (fat or external load) increases workload without increasing force-generating capacity

  • Walking with increased non-contractile mass elevates VO₂, heart rate, ventilation, muscle activation, and energy expenditure because greater muscular work is required to move and stabilize the heavier body during locomotion

 

Power output for treadmill exercise:

  • Work rate (W) = m x g x v x slope

  • M = body mass in kg, g = gravitational constant (9.81m/s2), v = treadmill speed in m/s, treadmill slope in %

 

Changes in power and height when jumping with increased non-contractile mass:

  • Jump height decreases because additional non-contractile mass reduced take-off velocity

  • Jump power increased because greater force was required to move the increased mass and this increase in mass outweighed the reduction in velocity as power = force x velocity

  • This depends on the individual. For example, the added non-contractile mass could be too heavy for the participant so no force would be produced

  • Usually max power is when the individual is at 50% of their max velocity

 

Discuss the implications of increased non-contractile mass on exercise and performance prescription:

  • Increased non-contractile mass has important implications for exercise and performance prescription because it alters movement economy, relative power output, mechanical loading, and physiological strain

  1. Reduced relative performance: non-contractile mass increases body weight without contributing to force production. As a result relative strength and relative power decrease, especially during bodyweight-dependent activities such as jumping, sprinting, change of direction, and endurance running. Although absolute power may sometimes increase under loaded conditions, movement performance often decline because acceleration is reduced

  2. Increased physiological demand: adding non-contractile mass increases oxygen consumption, heart rate, ventilation, and energy expenditure at a given workload meaning individuals work at a higher relative intensity during locomotion and exercise, causing earlier fatigue, reduced exercise tolerance, and slower recovery. Exercise prescription may therefore require lower initial intensities, gradual progression, and careful monitoring of fatigue

  3. Increased mechanical loading and injury risk: greater body mass increases ground reaction forces, joint compressive forces and tendon loading which raises stress on the joints and lower back. Consequently, high-impact exercise may need modification, particularly in overweight or deconditioned individuals (do low-impact modalities)

  4. Implications for power and resistance training: adding non-contractile mass can increase absolute power output because more force must be produced against the external load = supports the use of loaded jumps, sled pushes, and resisted sprinting for developing force production and neuromuscular power. However, excessive loading may reduce movement velocity too much, alter movement mechanics, and reduce specificity for explosive performance. Therefore, load selection should balance force enhancement and velocity preservation since power depends on both force and velocity

  5. Importance of body composition management: for many sports, especially running, sprinting, gymnastics and endurance running, relative power-to-body mass ratio is critical. Therefore, reducing excess non-contractile mass while preserving contractile tissue can substantially improve performance. This highlights the importance of nutrition, resistance training and conditioning strategies that maintain lean mass during weight loss

  6. Individualisation of exercise prescription: the effects of non-contractile mass vary depending on training status, strength levels, movement skill and sports demand. Therefore, exercise prescription should be individualised according to body composition, movement goals, injury risk and performance requirements

  • Increased non-contractile mass elevates physiological and mechanical demands while reducing relative movement performance, meaning exercise prescription should carefully balance load management, injury risk, conditioning demands and the maintenance of optimal power-to-body-mass ratio

 

Reading (Hunter GR et al. Exercise Training and Energy Expenditure following Weight Loss):

  • Purpose of study = investigated whether different types of exercise training could help prevent the reduction in energy expenditure that commonly occurs after weight loss

  • Authors focused on resting energy expenditure (REE), total daily energy expenditure, and physical activity energy expenditure after dieting

  • Background concept = after weight loss, the body often undergoes adaptive thermogenesis or metabolic adaptation = means energy expenditure decreases more than expected from the loss of body mass alone = maintaining weight loss becomes difficult and weight regain is common

  • Study design: participant were overweight premenopausal women. The intervention consisted of weight loss through caloric restriction followed by different exercise programs. Groups included aerobic training, resistance training, and no exercise/control

  • Main findings:

  1. Weight loss reduced energy expenditure: after losing weight total daily energy expenditure declines largely because body mass became lower = expected after dieting

  2. Exercise helped preserve energy expenditure: participants who performed exercise training maintained higher physical activity energy expenditure compared with non-exercising subjects = exercise partially counteracted the metabolic slowing associated with weight loss

  3. Resistance training was particularly important for preserving lean mass: resistance training helped maintain fat-free mass (muscle) which is strongly linked to resting metabolic rate. Because muscle is metabolically active tissue, preserving muscle helped attenuate reductions in REE

  4. Aerobic exercise increased physical activity energy expenditure: aerobic training increased daily activity-related energy expenditure, improving total caloric expenditure after weight loss

  • Key physiological idea = energy expenditure is strongly influenced by body composition, especially fat-free mass. Weight loss often decreases muscle mass, which lowers REE. Exercise training, especially resistance training, helps preserve muscle and therefore helps maintain metabolic rate

  • Practical implications: the study suggests that exercise should be included during and after weight loss, not only to increase calorie expenditure, but also to reduce the metabolic adaptations that favour weight regain. Combining diet, aerobic training, and resistance training may be the most effective for long-term weight maintenance

  • Main conclusion = exercise training attenuates the decline in energy expenditure that occurs after weight loss, with resistance training helping preserve resting metabolism through maintenance of lean mass