Benny Larsson

A New Concept For Isokinetic Hamstring: Quadriceps Muscle Strength Ratio

Conventionally, the hamstring:quadriceps strength ratio is calculated by dividing the maximal knee flexor (hamstring) moment by the maximal knee extensor (quadriceps) moment measured at identical angular velocity and contraction mode. The agonist-antagonist strength relationship for knee extension and flexion may, however, be better described by the more functional ratios of eccentric hamstring to concentric quadriceps moments (extension), and concentric hamstring to eccentric quadriceps moments (flexion). We compared functional and conventional isokinetic hamstring: quadriceps strength ratios and examined their relation to knee joint angle and joint angular velocity. Peak and angle-specific (50°, 40°, and 30° of knee flexion) moments were determined during maximal concentric and eccentric muscle contractions (10° to 90° of motion; 30 and 240 deg/sec). Across movement speeds and contraction modes the functional ratios for different moments varied between 0.3 and 1.0 (peak and 50°), 0.4 and 1.1 (40°), and 0.4 and 1.4 (30°). In contrast, conventional hamstring:quadriceps ratios were 0.5 to 0.6 based on peak and 50° moments, 0.6 to 0.7 based on 40° moment, and 0.6 to 0.8 based on 30° moment. The functional hamstring:quadriceps ratio for fast knee extension yielded a 1:1 relationship, which increased with extended knee joint position, indicating a significant capacity of the hamstring muscles to provide dynamic knee joint stability in these conditions. The evaluation of knee joint function by use of isokinetic dynamometry should comprise data on functional and conventional hamstring:quadriceps ratios as well as data on absolute muscle strength.

Effects of resistance training on endurance capacity and muscle fiber composition in young top‐level cyclists

Equivocal findings exist on the effect of concurrent strength (S) and endurance (E) training on endurance performance and muscle morphology. Further, the influence of concurrent SE training on muscle fiber‐type composition, vascularization and endurance capacity remains unknown in top‐level endurance athletes. The present study examined the effect of 16 weeks of concurrent SE training on maximal muscle strength (MVC), contractile rate of force development (RFD), muscle fiber morphology and composition, capillarization, aerobic power (VO2max), cycling economy (CE) and long/short‐term endurance capacity in young elite competitive cyclists (n=14). MVC and RFD increased 12–20% with SE (P<0.01) but not E. VO2max remained unchanged. CE improved in E to reach values seen in SE. Short‐term (5‐min) endurance performance increased (3–4%) after SE and E (P<0.05), whereas 45‐min endurance capacity increased (8%) with SE only (P<0.05). Type IIA fiber proportions increased and type IIX proportions decreased after SE training (P<0.05) with no change in E. Muscle fiber area and capillarization remained unchanged. In conclusion, concurrent strength/endurance training in young elite competitive cyclists led to an improved 45‐min time‐trial endurance capacity that was accompanied by an increased proportion of type IIA muscle fibers and gains in MVC and RFD, while capillarization remained unaffected.

Evaluation of a specific test in cross‐country skiing

Six Danish male cross-country skiers were studied during the end-of-summer and winter seasons. Their maximal oxygen uptake was measured while running on a treadmill and using a ski ergometer incorporating the double-poling technique. Maximal oxygen uptake during treadmill running and double-poling was correlated with performance, expressed as a ranking score during 10 ski races. The tests were undertaken in September, December and April. Upper body maximal oxygen uptake increased 5.8% from September to December, decreasing to 2.3% above the September level in April. Upper body work output (2 min at maximal intensity) increased 11.8% from September to December (P less than 0.05). The relationship between upper body and leg maximal oxygen uptake--the upper body/leg ratio--was 89.4% in September. In four skiers, both treadmill and upper body tests were undertaken on each test occasion. The upper body/leg ratio changed from 87.7% in September to 95.7% in December. In April, the ratio was 91.0%. The maximal oxygen uptake measured using the ski ergometer during double-poling was significantly correlated with performance (P less than 0.05). It is concluded that the upper body ski ergometer can be used in the evaluation of elite cross-country skiers.

Prevalence of asthma-like symptoms, asthma and its treatment in elite athletes.

The objective was to determine the prevalence of asthma‐like symptoms and asthma and the use of asthma medication in Danish elite athletes. A cross‐sectional questionnaire survey of Danish elite athletes was conducted in 2006. All elite athletes (N=418) financially supported by the national organization of elite athletes comprised the study group; 329 (79%) completed the questionnaire concerning their sport, asthma‐like symptoms, asthma and use of asthma medication. Asthma‐like symptoms at rest were reported by 41% of respondents; 55% reported asthma‐like symptoms at rest or at exercise. Physician‐diagnosed asthma was present in 16% and 14% had current asthma. Asthma medication was taken by 7% of the athletes, of whom 79% used inhaled corticosteroids and 21% used inhaled β2‐agonists only. Athletes participating in endurance sports had higher prevalences of current asthma (24%) and use of asthma medication (15%) than all other athletes (P<0.01). Athletes participating in endurance sports have a higher prevalence of asthma and use of asthma medication. The frequency of asthma medication is lower than the prevalence of current asthma indicating that there is no overuse of asthma medication among Danish elite athletes.

Isokinetic muscle strength and hiking performance in elite sailors

The aim of the present study was to describe the isokinetic strength profile and its relation to hiking performance in male (Sm, n=15) and fmale (Sf, n=6) elite sailors compared to a group of male control subjects (Cm, n=8) similar in age, anthropometry and level of fitness. Eccentric knee extension strength was higher in Sm compared to Cm. (P<0.01). Furthermore, Sm were stronger during trunk extension (P < 0.05), but not during trunk flexion compared to CM. Overall muscle strength was lower in SF compared to SM (P < 0.01) and CM (P < 0.05), except for eccentric knee extension strength, where SF and CM did not differ (P > 0.05). Hiking performance correlated to maximal eccentric and isometric knee extensor strength in SF (rs= 0.83–0.88, P < 0.05) and in CM (rs= 0.73‐0.77, P < 0.05) and to maximal eccentric knee extensor strength at high velocity in SM (rs= 0.46‐0.54, P < 0.05). For a subgroup of hikers in SM (n= 8), hiking peformance correlated to maximal isometric‐eccentric knee extensor strength (rs=0.67‐0.74, P<0.05), whereas no correlations emerged for the non‐hikers (n=7). Few correlations were observed between hiking performance and maximal concentric trunk flexor strength (rs=0.69‐0.92, P < 0.05). Unexpectedly, in SM correlations also were observed between hiking performance and maximal strength of the trunk extensors (rs=0.46‐0.53, hike subgroup: rs=0.64‐0.67, P < 0.05). In conclusion, notably high levels of maximal eccentric knee extesor strength were observed for the male and female elite sailors examined in the present study. Furthermore, the present results suggest that hiking performance depends in part on maximal isometric‐eccentric knee extensor strength. The maximal strength of the trunk extensors, which potentially stabilizes the lower back and spine, also seems to have some importance for the hiking performance of top‐level sailors.

Yacht type and crew-specific differences in anthropometric, aerobic capacity, and muscle strength parameters among international Olympic class sailors.

Abstract Physical fitness and muscular strength are important performance factors for Olympic class sailors, but the physical demands vary greatly between yacht classes, and limited information is available regarding the physical demands for the different crew positions. In the present paper, strength and aerobic capacity data from elite Olympic sailors are presented and compared with previous findings. Furthermore, a system for classification of Olympic class sailors is suggested. Peak aerobic capacity (peak oxygen uptake, [Vdot]O2peak) and maximal isometric and isokinetic muscle strength of the knee extensors and flexors were assessed, together with the hamstring/quadriceps strength ratio (H/Q ratio). Peak aerobic capacity (ml O2 · min−1 · kg−2/3) was as follows: males – static hikers (n = 5) 215, s = 7; dynamic hikers (n = 8) 252, s = 17; trapezing helmsmen (n = 6) 234, s = 15; trapezing crew (n = 10) 239, s = 16; females – dynamic hikers (n = 6) 194, s = 16; trapezing crew (n = 2) 200, s = 13. Strength data for hikers, presented as peak moments (normalized to body weight) obtained during eccentric, isometric, and concentric contraction (Nm · kg−1) respectively were as follows: males – quadriceps: 3.66 (s = 0.68), 3.97 (s = 0.66), 1.82 (s = 0.34); hamstrings: 1.93 (s = 0.22), 1.38 (s = 0.41), 1.05 (s = 0.21); females – quadriceps: 3.84 (s = 0.71), 3.81 (s = 0.58), 1.60 (s = 0.28); hamstrings: 1.75 (s = 0.23), 1.10 (s = 0.16), 0.84 (s = 0.13). The peak moment based H/Q ratios for slow eccentric and concentric contractions were 0.42 (s = 0.11) and 0.39 (s = 0.04) for males and 0.43 (s = 0.06) and 0.39 (s = 0.04) for females respectively. Elite Olympic class sailors demonstrated high [Vdot]O2peak values comparable to those observed in other non-endurance sports. The strength data revealed very high quadriceps strength for hikers, which is likely a result of the high muscle forces encountered during sailing, and a low H/Q ratio. To ensure optimal knee joint stabilization during sailing and other training activities, it is suggested that hikers should counter this strength imbalance by performing additional strength training for the hamstrings muscle group.

No effect of growth hormone administration on substrate oxidation during exercise in young, lean men

The purpose of this study was to examine the effects of increased fat availability induced by growth hormone (GH) administration on the oxidative metabolism during exercise. Seven well‐trained males (age 25 ± 2 years (mean ±s.e.m.); peak oxygen consumption : 62 ± 1 ml min−1 kg−1 (completed four randomised trials: 120 min bicycling at 55% 4 h after receiving either 7.5 IU (2.5 mg) GH or placebo (Plc), and during rest after receiving either GH or Plc. In all studies a standardized meal was given 2 h after GH or Plc injection. GH administration resulted in an ∼60‐fold increase in serum GH concentration at rest (P < 0.0001) and during exercise (P < 0.0001). The increase in serum GH was followed by an increase in circulating glycerol at rest (8%, P < 0.0001). When combined with exercise the increase in plasma glycerol was more pronounced (GH: 716% of baseline versus Plc: 328%, P < 0.0001). However, this increase in fat mobilization did not increase fat oxidation during exercise (indirect calorimetry). In conclusion, GH administration combined with aerobic exercise increased lipolytic parameters substantially more than exercise alone, but did not further augment whole body fat oxidation.

Exercise-induced rib stress fractures: potential risk factors related to thoracic muscle co-contraction and movement pattern

The etiology of exercise‐induced rib stress fractures (RSFs) in elite rowers is unclear. The purpose of the study was to investigate thoracic muscle activity, movement patterns and muscle strength in elite rowers. Electromyographic (EMG) and 2‐D video analysis were performed during ergometer rowing, and isokinetic muscle strength was measured in seven national team rowers with a history of RSF and seven matched controls (C).

Effect of eight weeks of endurance exercise training on right and left ventricular volume and mass in untrained obese subjects: a longitudinal MRI study.

The aim of the present investigation was to examine how 8 weeks of intense endurance training influenced right and left ventricular volumes and mass in obese untrained subjects. Ten overweight subjects (19–47 years; body mass index of 34±5 kg/m2) underwent intensive endurance training (rowing) three times 30 min/week for 8 weeks at a relative intensity of 72±8% of their maximal heart rate response (mean±SD). Before and after 8 weeks of endurance training, the left and the right end‐diastolic volume (EDV), end‐systolic volume (ESV), ejection fraction (EF), stroke volume (SV) and ventricular mass (VM) were measured by Magnetic resonance imaging (MRI). Submaximal heart rate decreased from 126±5 to 113±3 b.p.m. (10%; P<0.01), and from 155±5 to 141±4 b.p.m. (9%; P<0.001) at submaximal workloads of 70 and 140 W (110 W for women), respectively (mean±SEM). Resting ventricular parameters increased significantly: left ventricular SV, EDV and VM increased by 6%, 7% and 13%, respectively (P<0.01). The right side of the heart showed significant changes in SV, EDV and VM with increase of 4%, 4% and 12%, respectively (P<0.05). Eight weeks of endurance training significantly increased left ventricular SV and right ventricular SV, due to an increase in left ventricular EDV and right ventricular EDV. Furthermore, left VM and right VM increased. We conclude that using MRI and a longitudinal design it was possible to demonstrate similar and balanced changes in the right and left ventricle in response to training.

Exercise‐induced rib stress fractures: influence of reduced bone mineral density

Exercise‐induced rib stress fractures have been reported frequently in elite rowers during the past decade. The etiology of rib stress fractures is unclear, but low bone mineral density (BMD) has been suggested to be a potential risk factor for stress fractures in weight‐bearing bones. The present study investigated BMD in seven Danish national team rowers with previous rib stress fracture (RSF) and 7 controls (C) matched for gender, age, height, weight and training experience. Total body scan and specific scans of the lumbar spine (L2–L4), femoral neck and distal radius were performed using a DEXA scanner. The RSF subjects showed significantly lower L2–L4 BMD: RSF: 1.22±0.05 g cm−2 (mean±SEM) (median 1.19 g cm−2, range 1.02–1.37 g cm−2) compared to C: 140±0.04 g cm−2 (median 1.41 g cm−2, range 1.27–1.57 g cm−2) (P=0.028).The present results suggest that low bone mineral density may be a potential risk factor for the development of exercise‐induced rib stress fractures in elite rowers.