“Maximal Strength Training Improves Aerobic Endurance Performance” J. Hoff, A. Gran, J. Helgerud

1. “Maximal Strength Training Improves Aerobic Endurance Performance” J. Hoff, A. Gran, J. Helgerud

2. BackgroundInformation • Neural adaptation: Alterations in recruitment, rate coding, synchronization of motor units, reflex potential, and contractions of antagonist and synergist muscles • Ensure optimal neural adaptations in a strength training program: -stress all motor units, especially the high threshold motor units, to achieve maximal muscle activation • Maximal strength training increases the peak force: highest force developed during 1 repetition of a maximal voluntary contraction • Improvement in force development requires maximal strength training methods: high mobilization of force, high loads, & few repetitions per set

3. Introduction Purpose: To examine the different effects of a maximal strength training program that emphasizes maximal mobilization of force in the concentric part of the action Hypotheses: • 1. 1RM will increase • 2. Time to peak force at a submaximal strength load will decrease • 3. Work economy at an aerobic workload will improve • 4. Endurance performance will improve

4. Subjects and Apparatus • 19 male cross country skiers: Well trained with VO2max higher than 65mL/kg/min- Randomly assigned to HRT and CON • 2 days of pre-testing, 8 week training period, 2 days of post-testing • Maximal strength training and testing: - Modified cable pulley apparatus used to simulate poling movements -Performed pull downs • Ski double poling: - Simulated on ski ergometer - Athlete stands on freely wheeled platform & performs double poling movement against a load

5. Testing • 6 tests completed over 2 days: 3 strength tests, 2 tests on ski ergometer, 1 test treadmill Day 1: • Start with load as near to the expected 1RM as possible and increase load by 3kg after each successful lift • Performed test at approx 80% of 1RM, then a single series of 24 reps at 60% of 1RM - both tests measured PF and TPF • Treadmill Running- 6 degree inclination to determine VO2max Day 2: • VO2 peak assessed using 4 degree inclination on ski ergometer • Initial speed: 171 m/min, increased 2 minutes to 181m/min, then 2 more minutes to 198m/min • Calculation of work economy

6. Results HRT GROUP VS. CON GROUP: • (HRT) 9.9% improvement in 1RM- (CON) not much of change • (HRT) PF at 60% and 80% of 1RM improved from pre to post test vs. CON unchanged • (HRT) showed significant decrease in TPF from pre to post test • HRT & CON both enhanced their endurance performance -time to exhaustion was longer after the training period by 56% & 25% respectively • (HRT) Work economy improved significantly from pre to post test at speed of 181m/min

7. Discussion • Maximal strength training with emphasis on maximal mobilization of force in the concentric action improves work economy on an aerobic workload & thus improves aerobic endurance performance -correlated to the enhanced rate of force development & to changes in PF & 1RM • A small increase in maximal strength paralleled with a great increase in TPF indicates that the rate of force development seems to be more important than the improved strength • Improved work economy: -might be due to the improved 1RM or improved rate of force development

8. Discussion Continued.. • The results from this study show that a small change in 1RM has a huge effect upon endurance performance - the training for an enhanced 1RM leads to large changes in PF and TPF • These findings also show that the increase in rate of force development might be a more important factor for improved work economy, and thus improved endurance performance as apposed to strength gains • The current results suggest that cross country skiers improved their PF and TPF after the strength training regime with emphasis on maximal mobilization of force in the concentric action -highlights the importance of other strength parameters rather than focusing only on maximal strength

9. Conclusion • This article can be beneficial when designing endurance training programs for athletes as well as for rehabilitation • When wanting to improve endurance performance in athletes, we as kinesiologists should focus on strength training with a strong emphasis on maximal mobilization of force • The effects are likely to be beneficial for both upper and lower body regimes

10. Joint Loading in the Lower Extremities during Elliptical Exercise

11. Introduction • Elliptical trainers (ET) simulate walking, but with reduced impact loading • Disadvantage of level walking: repetitive vertical impact forces at heelstrike may lead to musculoskeletal injuries • Elliptical exercise (EE) is a low-impact aerobic exercise modality useful for developing and maintaining cardiorespiratory fitness. • Often used in rehab programs involving patients with hip and knee problems or those with diabetes

12. Introduction • EE decreases the effects of repetitive impact loading like that seen in level walking • Feet are in constant contact with the pedals, forming a closed kinetic chain • Not all knee injuries are do to impact forces • eg. cyclists : knee injuries due to inappropriate pedal design and ankle positioning

13. Purpose • To gain a better understanding of the loading of the lower limbs during EE compared to that of level walking • To suggest improvements that can be made to the ET’s design • To help establish guidelines for safe use of the ET for healthy users and those in rehabilitation programs

14. Methods • 15 healthy male adult volunteers of similar age, height and weight • Joint loading was measured and compared between EE and level walking • Subjects first performed level walking on a modified walkway • Step length and cadence were calculated and used to program the ET • an average pedal rate of 50rpm was maintained with the aide of a metronome

15. Results • Angular patterns at the knee and hip were similar, but EE had significantly greater peak flexion angles at the hip, knee and ankle • Throughout the entire EE cycle, the ankle remained internally rotated • During EE the knee had greater peak abduction angles

16. Discussion • Results due to the rigid pedal trajectory and the closed kinetic chain motion • EE reduced the impact of heel strike • decrease the risk of developing tibiofemoral joint osteoarthritis • Greater knee extension during EE causes increased loading of the quadriceps • increases the contact force at the knee • Injury? • could lead to early fatigue of the quadriceps • Limit duration?

17. Conclusion • Need to consider users’ knee joint function and muscle strength in order to avoid injury • Could be resolved by reducing the slope of the pedal ellipse and increasing the mobility of the pedal system • Improve efficiency of the knee and hip and reduce fatigue and overuse injuries

18. Effects of Obesity on the Biomechanics of Walking at Different Speeds

19. Introduction • Obesity is the most preventable risk factor associated with large joint osteoarthritis • Walking is the most prescribed form of exercise for people with obesity, but may lead to OA • Obesity increases the loads involved in walking, and these loads increase as speed increases

20. Purpose • To measure how obesity affects walking biomechanics, especially in regards to knee-joint loads, by determining the ground reaction force (GRF) and lower-extremity sagittal-plane joint moments across a range of walking speeds

21. Methods • Two groups of young adults volunteered • One obese group • One normal-weight group • Each subject performed 6 level walking trials on a dual-belt force-measuring treadmill • Subjects familiarized themselves with treadmill by walking for 10 minutes • Each trial had a different speed ranging from 0.5 m/s up to 1.75 m/s and subjects walked for 2 minutes with one leg on each treadmill and then for 2 minutes with both legs on the right (GRF) treadmill.

22. What was measured? • GRF - by treadmill • Kinematics - footswitches and high-speed video • Net muscle moments - to calculate sagittal-planes about the hip, knee,and ankle • Step width - by calculating distance b/w the midstance center of pressure location. • Done when subjects walked with both feet on right treadmill

23. Results • Absolute GRF was greater for obese individuals, and was decreased at slower walking speeds for both groups • Temporal strides were similar b/w the two groups • Stride length and frequency were the same

24. Results • Obese individuals spend more time in stance phase and less in swing phase • Absolute net muscle moments were greater in obese individuals and decrease at slower speeds for both groups • Step width was 30% greater in obese subjects with all walking speeds

25. Discussion • Obese individuals walk with greater joint load, and walking slower will reduce this load • During stance, no significant difference in knee-joint flexion was found • Moderately obese adults walk with similar joint kinematics • As obesity increases, individuals adjust their gait to reduce knee-joint loads

26. Conclusion • This study can be used to determine a biomechanically appropriate level of exercise for obese individuals • Limitation was this study did not account for limb rotation • GRF was greatly increase in obese individuals, but there was no change in sagittal-plane kinematics • Walking slower results in less GRF and net muscle moments, supporting that slower walking may reduce the risk of musculoskeletal pathology in obese individuals