Reddit mentions of Grip Pro Trainer Hand Grip Forearm Strength Gripper 30, 40 & 50 lbs Full Set of All 3 Weights

I do agree with the others that practicing once a week is less than ideal, but I it seems like I'm disagreeing with several folks in saying that physical muscle strength is very important. It is also important to know what muscles to exercise and how to exercise them. Anaerobic muscle groups (not powered with oxygen) are the most important for kendo. These are your "fast twitch" muscles. On the other side there is aerobic muscle groups (they are powered with oxygen). These are commonly known as "slow twitch" muscles. Most people (incorrectly) use their slow twitch muscles to do kendo. When the sensei says "you're too tense" it's because you're using your larger slow twitch muscles. When the sensei says "you're using too much power" it's because you're using your slow twitch muscles. Basically, a lot of form, posture, etc., problems come from people using slow twitch aerobic muscles.

So the question is, how do you use anaerobic muscle groups instead? These muscles tend to be a lot smaller. They're also harder to feel and use if you haven't used them a lot in the past. I'm fairly certain most people don't know these muscles exist, but they're there. In order to use them (in most kendo-related cases), you have to relax your bigger slow-twitch muscles. They have to go limp. Then, fast twitch can take over. Lifting the shinai over your head, doing okuriashi, swinging, te-no-uchi, holding a strong kamae... you need strong fast-twitch muscles for all this. MANY people spend years and years (and sometimes their entire kendo careers) building the wrong muscle groups because if they switch, they'll become weak and slow again. Slow-twitch muscles allow you to do one cut (a really hard and painful one, usually). You can do a pretty fast swing this way too. So people think they can get by and improve, but they always hit a wall, and usually end up injured at some point. If I had my way beginners would just exercise the right muscle groups before they're allowed to swing a shinai. Sort of like how a lot of kyuudo dojos do, in a way. Until these (weird, normally unused) muscles reach a certain point, you'll be physically incapable of doing correct kendo.

Basically, that's a long way of saying you should definitely be exercising these muscle groups at home as much as you can. There's a magic base-line for fast-twitch muscle strength that will physically allow you to do kendo correctly. Without a high enough base strength, you'll never swing without tensing up. You'll never move your feet really quickly. Basically, you'll never hit that "elite" level and your cap will be "okay" and maybe "somewhat good." You'll start to feel the difference after a month or so. You'll notice you're using your left hand more than your right. You'll start to actually feel te-no-uchi. And, your shoulders will be strong (and relaxed).

With that in mind, here's my daily home routine. Note: I actually use a lighter shinai (37) with all of these. It allows me to focus on form, te-no-uchi, etc. But, it also prevents me from using aerobic muscle groups when I'm getting tired.

1. Lunge w/ cut (horizontal to the floor). Knees should be at 90 degree angles, so don't over extend. Focus should be on keeping back straight, using te-no-uchi- at the end of your cut, and driving your center of gravity straight down below your core.

2. Matawari. Similar to #1. Keep your back straight and drive the center of your core straight down.

3. Grip Training. I use these donuts. Squeeze using pinky and ring finger. Both hands.

4. Katate Suburi. Just left hand. Focus on the form of the swing. If you can't swing with one hand without tensing your shoulders, choke up on the grip. If your floor is too high, sit on your butt with legs outstretched and back straight. This'll work out your core some. Then, switch to right hand (holding in the position your right hand normally would). Focus on relaxing and not using your right hand much on the swing, and then practice squeezing at the end for te-no-uchi. Shouldn't be a workout for the right arm katate-suburi. Just practice for good form and not using it.

5. Small Katate Suburi. Same thing as #4, but you're practicing hisashi-men with one hand. Focus on not letting your shoulders roll forward, tense up, etc. And, practice the te-no-uchi at the end. You can do this one standing with short ceilings.

6. Okuriashi w/ Metronome. This is so I can actually measure progress in okuriashi improvement. Each tick on the metronome is either right foot moving forward or left foot coming back into position. Tick: Right foot goes forward. Tick: Left foot catches up. Start with a slower speed that is easy and focus on keeping your center of gravity right in the middle of your feet. Then, slowly speed it up until you find your ceiling. From there, you can increase the speed little by little and get your okuriashi faster. This'll also be a really good workout for the weird muscles required for good okuriashi when you're pushing your ceiling speed up.

As for how many / how much of the above you should do... I don't actually have a number for you. I just do each of the above until I feel slightly uncomfortable, then stop. Then I write down the number / time / etc., on a spreadsheet so I can track it. After going through all 6 (you don't have to use the order above, I tend to go back and forth between things), do it again until you've gone through all six four times. For the first three times through, just go until you're somewhat uncomfortable then stop. For the final set (fourth time through), do as many as you can. Main thing is you're increasing your averages slowly over time. The important thing is consistency and exercising even when you're tired. In fact, the only way to get better is to exercise when your muscles are tired. This actually activates gene sequences in your DNA that tell your body to get stronger. If you don't stress your body enough (i.e. be consistent and do your exercises every day) this won't happen, and your muscles won't actually get physically stronger. Exercising once, and then letting yourself recover fully is almost as bad as not exercising at all. Your body will always try to change itself so that it feels comfortable, so if you're always sore and working out, your body will try and catch up to that. Once it does, you have to up the ante.

With anaerobic muscles, you don't want to push them really really hard. They're more like "sprinter's muscles," so they can't take a ton of stress over long periods. Also, if you keep working them out beyond "somewhat uncomfortable" you're not getting much benefit out of that. The most efficient (and safe for injury) method is to stop when you're feeling it a little bit, then move on to another exercise while you let your muscles recover (they'll recover quickly--in minutes--if you're actually using anaerobic muscles).

One other thing I'll add... I do think endurance is important, but if you do proper technique, and build up anaerobic muscle groups, high-endurance activities get a lot easier. When you're not tensing and using your big muscles, you move much more freely and can do kendo a lot longer. My dojo is one of the toughest for endurance I've been to (and I've traveled around quite a bit). It only got easier after I started working on anaerobic muscles. No matter how good at running I got before, practice was still killer. Really, kendo is more like sprinting than long distance running... though some could argue it's a bit like long-distance sprinting. There's a reason why the high-ranking sensei can do kendo for a really long time. You also don't see them breathing as hard as everyone else. Part of it is efficiency in their skill, but another part (I believe) is that they use muscle groups that don't use oxygen to power them. So, no need to breathe so hard. Faster recovery. etc.

tl;dr Exercise your anaerobic muscles

Depends on how cheap you want to go. When my grip was failing I bought some grip trainers off Amazon.

You can also do rice buckets on the super cheap end (still very effective, but not as convenient), or the expensive metal spring kind.

I use these at work while I'm sitting at my desk. Engage not just my forearm but the whole arm and it works pretty well.

http://www.amazon.com/gp/product/B000NJHD1W/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

This will help. This tool is actually very popular in Russia and other former Soviet states.

Are the grip training rings/donuts any good? They have some good stars on amazon and are a lot cheaper than the COCs:

http://www.amazon.com/Grip-Pro-Trainer-Forearm-Strength/dp/B000NJHD1W/ref=sr_1_3?ie=UTF8&qid=1367903326&sr=8-3&keywords=grip+trainer

To be honest, I haven't been able to overcome losing finger strength between gyms. It's a real bummer every time I get back to it. The hangboards I travel with are the most compact I've found, but without a reliable bar to hang them from (not to mention having to fit one or two in a 24L bag), your best bet might just be something like these babies.

Warm up, and do a bunch of holds to failure. Easy to do absentmindedly and during transit and such. Not perfect, but definitely better than nothing.

Also keep an eye out for doorframes! If you're lucky, your accommodations might have a strong enough one to hang from