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

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

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

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

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

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

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

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

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

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

Joint Loading in the Lower Extremities during Elliptical Exercise

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

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

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

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

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

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?

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

Effects of Obesity on the Biomechanics of Walking at Different Speeds

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

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

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.

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

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

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

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

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

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