Monday, November 17, 2003 - Physiology
Strengthening Exercises - Do They Improve Performance? (Part 6 of 6)

- By: Ross McKinnon, PT

The tests and exercises described should be performed with the help of a physiotherapist or strengthening coach to achieve maximal benefit.

Strengthening exercises are advocated for most sports including cross country skiing. The logic is that cross country skiers need to improve power to help increase ski velocity. Power is important as roughly 50% of race time is spent on uphills. The best way to improve power is through both endurance and resistive exercises. Strength training is a great way to provide resistance and gain power. Therefore skiers should use resistance training. However, does weight training improve ski performance? If it does which exercises should an athlete perform, how often and how many. Can power and strength be developed without sacrificing endurance? Unfortunately with most questions this is not easily answered as most of the information is based on anecdotal evidence, the research that has been performed is minimal leaves many questions unanswered. In this article I would like to briefly review the information available.

PHYSIOLOGY
A basic principle in muscle physiology is that to improve performance a muscle must be trained with movements as close as possible to the desired movement or skill (McCardle et al). In other words muscles that are trained in a particular range of motion and/or angle will show the greatest strength improvement in that range this is termed angle-specific training.

Improvements in a muscles force production with strength training are related to:
1) Psychological Factors: research has demonstrated improvements in strength can be achieved with appropriate arousal levels, concentration, etc.

2) Muscular Factors

a) Muscle Hypertrophy – resistance training will result in hypertrophy of muscle fibers which in turn help generate tension
B) Muscle Fiber composition – the latest research supports that the percentage of slow to fast twitch fiber composition is static through life. There does appear to be one type of muscle fiber that has both slow and fast twitch qualities. These muscle fiber types can somewhat adapt to either slow or fast twitch based on the demands place upon them. What is more important here is that muscle fibers will increase their strength in relation to the demands placed upon them with training. Slow repetitions will train the muscle fibers to contract slowly whereas fast repetitions will train the muscle fibers to contract slowly. Again specificity is key. It is thought that fast twitch muscle fibers have a greater ability to improve their force generating properties than slow twitch muscle fibers. On the other hand slow twitch muscle fibers have a greater proportion of the cells that allow the muscle fiber to work aerobically. Focusing only on high load exercises is thought to provide greater develop of the force generating properties at the expense of the endurance properties. The opposite is thought to be true of endurance training.

3) Neuromuscular Factors- the initial strength gains noticed in strength training programs are largely related to improved neural organization and motor unit recruitment. i.e. the brain gets better at organizing the muscles needed for strength performance. This is a very important point to remember that again specificity is crucial; skiers don’t really need to get good at doing leg extensions. Doing leg extensions does not necessarily translate into improved ski technique. Restated, performing a certain exercises allows the body to organize the firing of motor-units to provide power for that exercise. This may not carry over into an individual skill.

4) Energy Pathways – (from McCardle, Katch and Katch) Different training will determine which of the bodies energy systems are used. For exercise of short duration i.e. the 100m sprint or power lift the body will use the energy already stored in the muscle these are termed ATP and CP. For short duration exercise less than 2 minutes the body will rely on the anaerobic glycolysis reaction. Beyond 2 minutes the body will increasingly rely on the aerobic system for energy. These energy pathways are also trained depending the demands place upon the body.

RESEARCH
I have included a few research articles briefly summarized and criticized, this is by no means a comprehensive review.
Research has shown that upper extremity power relates to ski velocity in both elite and sub-elite cross country skiers. Hoff et al researched strength training using a pull down motion similar to double poling on a cable machine. The subjects performed 3 sets of 5 repetitions with 2-3 minutes rest between sets at 85% of one repetition max (1RM). The load was constantly increased so that the athlete could do no more than the 5 repetitions, emphasizing explosive performance. The researchers found that skiers who utilized this form of training made a significant increase in double poling endurance, 1RM strength and time to peak work force. No decrease in VO2 max or threshold was found This study was small with only 19 subjects, but did include a control group. The key here is that the researchers used a strengthening device to closely simulate double poling and emphasized explosive power not slow repetitions. The researcher theorized that this type of training will help develop faster nerve reactions. Remember that this study was only carried out for 8 weeks and no longer follow-up was performed i.e. were the gains maintained, and if so for how long? How soon would the strength begin to diminish once the training was completed? This style of training was only studied in the upper body and may not be applicable to the lower extremity. With only 8 weeks of training it would be expected to see strength gains primarily related to increased motor unit recruitment rather than muscular hypertrophy as the authors concluded.

One other study on skiers done by Paavolainen et al examined a combination of strength and endurance training on aerobic and neuromuscular performance. The study was conducted over 6 weeks for 6-9 sessions per week. Seven skiers used 34-42% explosive training (i.e. plyometrics type exercises and 80% of 1RM max squats) as well as 66-58% endurance training. The control group of eight skiers used 85% endurance and 15% endurance type strength exercises i.e. higher repetition arm and leg exercises. The researchers found no decrease in V02 max in the explosive strength group. The researchers found that the explosive group in jump height and in time to develop rapid isometric power. An interesting analysis is made by Hawley in an article on strength training which can be found on the sportsci.org website. He feels that these improvements are meaningless as skiers don’t need rapid isometric force production or the ability to jump high. This is a good point, meaning that the research shows that power can be increased but is it specific to skiing? The research would be more applicable if an improvement was demonstrated in a ski specific activity.

A recent study by Miller et al on triathletes found that combination of endurance training and resistance training improved running economy, hopping power and strength compared to endurance training alone. Similar to the Hoff study the resistance exercises were performed with 3-5 reps at >90% of 1RM max 2 times a week.

Other research in other endurance based sports such as cycling and running has shown that strength training does not interfere with endurance activities. Hawley on the other hand reviews 3 other non-ski research articles examining strength and endurance training. Cycling, swimming and rowing were studied. These three articles do not support the use of strength training finding it detrimental to endurance capabilities. Two further articles he reviewed did find positive benefits, however they used minimally trained subjects. Minimally trained subjects should show improvement with any form of exercise. Hawley concludes that “highly trained athletes who are already capable or generating high power outputs in their chosen discipline, further improvements in strength are a less important factor in enhanced endurance performance…modern training studies do not support the use of resistance training programs for improving the performance of highly-trained athletes”.

However, Hawley may not be familiar with modern ski racing. Skiing is and always will be an endurance based sport. However skiing is increasingly becoming a power-endurance sport. As previously mentioned a typical race involves 50% of the time spent on an uphill. The steeper the uphill the more power required. Modern ski racing will increasingly require power for mass starts, sprints (both as an event and at the end of mass starts races), sprint relays, and uphills.

PERIODIZATION:
Much of this information is taken from the NCCP level II technical manual. Each period is a standard 4 week period.

Core strength should also be added to this table performed three times weekly through periods 1-9 then reduced to 1x weekly. (See Part IV)

GENERAL STRENGTH:
Sets and Repetitions:
There is very little scientific information on the correct number of sets and reps for skiers other than the aforementioned articles. Most of the information is based on experience and personal beliefs. Should all strength be performed to the maximum with low reps and high weight?

1RM is the basis for most strength training programs. 1RM (one repetition maximum) is the amount of weight an athlete can lift once using the correct technique. 10RM maximum is also commonly used and is the maximum weight an athlete can lift for 10 repetitions using the correct form. Athletes attempting weight training using these formulas should be familiar with the weight training technique and be supervised by someone experienced with weight training.

Typical general strength training consists of 3 sets of 10 repetitions, power strength training 3 sets of 6-8 repetitions and endurance training of 3 sets of 10+ repetitions.
Other ski coaches advocate a set of warm-up 10-12 repetitions then 2 sets of 6-8 repetitions. Other research mentioned above advocates a high weight low rep program.

The NCCP level II manual recommends general strength be performed at 75% of 1RM maximum for 10-12 repetitions. The manual recommends 3 sets with adequate rest between.

Total work should take 45 – 60 minutes not including warm-up.

Another strength formula is called the DAPRE (daily adjustable progressive resistive exercise) formula.

With any of the above recommendations remember there is no right of wrong number of sets and reps. Remember the basic principles: exercises should be performed to local muscle fatigue, exercises must be performed with snap, and you must get adequate rest between sets. Try to be as ski specific as possible.

Exercises include (for further ideas check out your local bookstore or library):
Back Exercises:
Back-Ups (Roman Chair)
Prone Back-Ups
Prone Pointer

Abdominal:
Curl-Ups
Leg Twists
Crunches
V-Sits
Twisting curl-ups
Side curl-ups

Arm Exercises
Bench press
Chin-ups
Lat pull downs
Triceps pull downs
Deltoid Flyes
Bent arm pull overs
Dips
Push ups – regular, soccer ball

Leg Exercises
Half squats
Split squats
Single leg squats
Hamstring curls
Leg press
Leg extensions
Calf raises straight leg
Calf raises bent knee

POWER STRENGTH PROGRAM - Plyometrics
The NCCP coaching manual recommends Power Strength workouts which are basically plyometric type exercises. Here is a brief review of plyometrics.

Our body constantly uses the elastic and energy storing properties of tendons and muscle. As a skier each time we stride forward and our ski hits the snow energy is stored in the quadriceps and Achilles tendons as they are loaded, this energy is then returned to provide propulsion as the lower extremity pushes off. In skiing this is termed preload and utilizes the principles behind plyometric training. Plyometric training uses the principles to provide more load and speed to exercises. Plyometrics work to both increase the speed of muscle contraction, increases the number of muscle cells that are recruited, and trains the neuromuscular pathways.

To maximize the stored energy a few things must first happen

  • The energy stored must be attained actively i.e. an eccentric contraction. An eccentric contraction involves the muscle actively working and lengthening. We are typically stronger eccentrically than concentrically.
  • The time between the shift from eccentric to concentric must be as short as possible to fully utilize the stored energy. You want a quick snap not a long push. The time of the transition is termed the ‘amortization’ phase.
  • A shorter ‘amortization’ phase requires that quality training is the key. An athlete must stop plyometric training once the ‘snap’ begins to disappear. The snap disappears as the muscle energy storage becomes depleted. This energy system also requires 30 seconds to 3 minutes to return. Therefore an athlete must experiment with rest times to allow proper recovery to maintain ‘snap’.
  • A general guideline provided by the National Strength and Conditioning Association is that an athlete should be able to squat a minimum of 1.5 times their body weight before starting structured plyometric training.

    Some examples of plyometric training:
    Repeated broad jumps
    Repeated single leg hops up a hill
    Box jumps, landing the springing off jumping again
    Classic balance hops
    Classic preload hops
    Skating balance hops
    Skating preload hops
    Skating cross leg hops
    Broad jump repeats
    Medicine Ball Upper extremity
    Hop overs
    Tuck Jumps
    Plyoball sit ups
    Marching Hops

    Athletes and coaches wanting more information on plyometrics should read the bible on plyometrics written by Chu (1999) Jumping into Plyometrics. Human Kinetics. Champaign, IL.

    ENDURANCE STRENGTH WORKOUT
    These workout can last anywhere from 10 minutes to an hour.
    Double pole only
    Skiing without poles
    Weight shorts skiing
    Roller board
    Pulleys

    MY SUGGESTIONS

  • There is very little research done on strength training for endurance based sports. Furthermore as with any training what works for some will not work for others. Knowing how your own body responds to training and working with a coach is always crucial. Constant monitoring of the effectiveness of training should always be incorporated.
  • Based on the limited research available skiers should think of incorporating the low reps high resistance approach mentioned in the research articles.
  • As I have tried to stress in previous articles you must have a stable core before you can properly focus on strengthening. You must be able to control a movement before you can focus on increasing the velocity of that movement. The core must be properly stabilized during resistive training so that the stabilization becomes second nature.
  • An athlete must train using correct breathing techniques (see previous articles)
  • The joint angles required during skiing should be used during resistive training. The large ankle and knee flexion angles should be reproduced.
  • Resistive exercises should be performed at a similar velocity required for elite skiing. Long labored pushes are not needed. Train the muscles at the speed required for skiing. Diagonal striding has a stride frequency of around 1.6 strides per second.
  • Skiing requires muscles to work in multiplanar ranges of motion – the exercises should therefore be multiplanar.
  • Try to incorporate balance into the exercises. Last year the National ski team had some great pictures on skifaster.net of doing upper extremity pulleys while working on balance.
  • Resistance training should be challenging but remain fun.
  • Given the need for specificity with strength training ski specific resistance training i.e. roller skiing poling only or without poles, roller board, etc. should be highly emphasized, possibly earlier in the year?
  • Resistance training should be highly individualized with specific goals in mind. For example a skier with greater natural endurance (slow twitch fibers) may want to spend more time on developing the fast twitch fibers through resistance training. The evolution of sprints will change a skiers training and further emphasize the need for power and resistance training.
  • If an athlete is limited for time, emphasize core and upper extremity exercises.
  • With the increasing popularity of sprint events specialization in events will continue to occur. ‘Sprinters’ will train more like middle distance runners.
  • In my experience the more difficult the conditions i.e. cold dry snow, poor wax the more an athlete will rely on upper body strength.
  • In observing sprint events and sprints for the finish in longer races upper body power and speed (turnover) are critical factors.
  • Ross McKinnon is a former ski racer now working as a physiotherapist at Rutland Physical Therapy in Kelowna, BC. His interests include improving an athlete's performance through the use of specific exercise. For further questions he can be contacted at or at . Ross provides individual evaluations to help improve performance and prevent injury.

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